John Porter

GPs at the Tradeshow: Looking for snake oil and finding…..the dirt on tillage

The Annual Meeting and Professional Improvement Conference of the National Association of County Extension Agents is that one time of year where extension agriculture professionals gather to share ideas, give talks, network, and let their hair down. The name of the organization is a bit outmoded: many states no longer call their extension personnel agents, but rather educators, experts, professionals, area specialists, and the like. Most aspects of agriculture are included: from the traditional cows and plows of animal science and agronomy to horticulture and sustainable agriculture (I’m the outgoing national chair of that committee). There’s also sharing on agriculture issues like seminars on engaging audiences about genetic engineering, teaching and technology like utilizing social media and interactive apps, and leadership skills.

It is the one time every year or so that Linda Chalker-Scott, grand founder of the Garden Professors, and I get to hang out. If we’re lucky we’ll meet up in some sessions, chat in the hallways, or grab a drink. But one of our favorite conference activities is taking a turn around the trade show floor. This is where companies and organizations are vying for the attention of extension educators to show them their newest equipment and products….we are, after all, the people that share growing and production information with a great number of potential clients across the country.

Since the organization runs on money, almost no company that comes calling with the money for a trade show spot is turned away. This means that the products may or may not stand up to the rigors of scientific accuracy. In years past we’ve found snake oil aplenty, like magical humic acid that is supposed to be this natural elixir of life for plant growth. The only problem is that humates don’t exist in nature and there’s little documentation of any effect on plant growth. The product that was supposed to be this magic potion was created from fossil fuels and no actual peer-reviewed research was offered by the company – hardly convincing. There were magic plastic rings that supposedly acted as protective mulch around mature trees and could slowly release water, except that mature trees don’t really need protective mulch and the amount of water would be negligible to a tree that size. So will we be smiling or scowling when we’ve made our way through the trade show.

Right off we set our sites on a company starting with “Bio”, which can be a good indicator of questionable rationale. That lit up the first indicator on our woo-ometer. Beneficial bacteria you apply to plants/soil: woo-ometer level two. So LCS and I engaged the representative. Asking about the product and what it does. We learned about their different products that could help increase the rate of decomposition of crop residues in farm fields, of turfgrass improvement, increased crop production, and treatment of manure pits on dairy and hog farms (which, if you’ve ever experienced one, you’d know would benefit from any help they can get in terms of smell).

Most of the products like this give vague descriptions of the beneficial bacteria it contains. They’re akin to compost teas that can have any number of good, bad, and downright ugly bacteria and fungi in them. Since you don’t know what’s in these products, any claims on soils or plants are suspect at best. However…our rep went on to tell us that the company created blends of bacteria from specific strains that had been researched for their effects on decomposition, soil nutrient availability, and plant growth. There was a brochure with the specific bacteria listed, along with studies the company had conducted.

We asked about peer-reviewed research, which is our standard for evidence here at the GP, and while he had no results to share he assured us that university-led research is currently in the works. And as we’ve stated in regards to applying of beneficial bacteria to soil – while there’s little evidence showing the effectiveness of applying non-specific bacteria to plants, using directed applications of specific bacteria which have been tested for specific functions are supported by research. So our woo-meter didn’t fully light up. We reset it and continued the hunt.

We scoured the rest of the trade show and found one other soil additive that lit up the first lights of our woo-meter, but the rep must have been out for lunch so without anyone to talk to we couldn’t confirm woo or no-woo.

However…..we did find something spectacular! The local employees of the USDA NRCS (Natural Resources Conservation Service) had an interactive demonstration of soil, specifically showing the benefits of reducing or eliminating tillage. The NRCS works with many farmers to incorporate conservation practices on farms, including no-till production, by providing technical assistance, farm plans, and even grants, cost-share, and easement programs. Many farmers have benefitted from their grant for season extension high tunnels (which are seen as a soil conservation technique, since they shelter soil). We were so enamored with the demonstration, we asked them to do it again…so we could record it. So, for your viewing pleasure check out the video below where you can see how well no-till soil holds its structure while tilled soil falls apart. This effect is from the exudates from all the beneficial microbes in the soil that act like glue to promote good soil structure. We’ll let the video speak for itself……

So not only does the trade show get a smile instead of a scowl from us, but also two thumbs up! Either there has been some weeding out of the trade show sponsors, maybe the snake oil salesmen didn’t get the traction they were hoping for at the conference, or hopefully some of these companies have failed to reach an audience with their pseudoscience.

Testing, testing, 1-2-3: Trialing new plants for the home garden

How do you know that plants will do well in your garden? Do you research the types of plants for your region, study different cultivars, and select only things that have been proven to do well for your conditions? Or do you buy what catches your eye at the garden center, plant it, and then see what happens? I used to joke that my home garden was a horticulture experiment station, since I’d try all kinds of random plants or techniques and see what works for me. Now, I get to do that as a fun part of my job through the All-America Selections (AAS) program. You’ve likely seen the AAS symbol on plants or seed packets at the garden center or in catalogs. Heck, you may even have them in your garden (and not know it). I compare it to the “Good Housekeeping Seal of Approval” that you used to see on appliances, cleaners, etc. The AAS program is a non-profit started in the 1930’s with the goal of evaluating new plants so that home gardeners can purchase high quality seeds and plants and to assist the horticulture industry in marketing innovations from their breeding programs. You can read more about AAS and its history here.

A few weeks ago I traveled to Chicago for the All-America Selections (AAS) Annual Summit to receive their Judge Ambassador Award. I had signed up a few years ago to be a trial site for edible crops for AAS. The following year I talked my colleague Scott into signing up as a judge for their ornamental trials. The fun thing about the program is that we get to grow all kinds of vegetables, fruits, and flowers that aren’t even on the market yet. We get to see how well they grow compared to similar plants and rate them on a number of factors including growth habit, disease resistance, and performance plus flavor (for edible crops) or flower color/form (for ornamentals). It can be hard work, but it is rewarding to help identify true plant innovations and to see your favorites be announced as winners.

How the testing works
While the AAS Trials may not have the rigor of academic crop research, I do appreciate the procedures in place that provide objective and high standard results.

Breeders, developers, and horticultural companies submit their new plants that are planned for future introduction to the board of AAS for consideration in the trialing program. During the application process, novel traits of the plants are identified to ensure that the plant offers something new and exciting – these are the traits that judges will observe and score. The board reviews the application to determine if it fits within the program rules.

One great thing about the program is that trial judges are professional horticulturalists from universities, seed companies, botanical gardens, etc. – they’re people who know how to grow things and know what quality plants look and act like. There are trial sites all around the country, providing for replication and generalizeable results for most regions of the country. The conditions plants are grown in also vary by location. My trial is at a farm where management is minimal. When we were at the summit we visited the trial gardens at Ball Horticulture which looked much more maintained and pampered compared to mine. This gives data on a variety of maintenance levels as you’ll find in home gardens – some gardeners are very conscientious about maintaining their plants and others have a more laissez faire approach. In order to win as a full national AAS winner, the plants have to perform well across the country in all these different situations. Sometimes those that perform well in a few regions but not the others will be designated as regional winners.

Second, the tests are blind. This means that we do not know what the exact plant is, who the breeder or seed company is, or any other info other than what type of plant it is. To the judge, each entry is just a number. It could be from a seed company you love (or hate), your best friend, the breeder who was your advisor from grad school, etc. This makes the results fair and reduces the chance for bias toward or against a plant based on its origins. The ratings are just based on the plant.

Another part of the trial is comparison. It is one thing to grow a tomato plant and say “yep, that’s a good tomato.” Its another to grow a tomato and compare it to similar cultivars to say “yep, that’s a good tomato….but it is better than what’s already available on the market.” The goal of the program is to show how new plants have merit over older plants. We only need so many new tomatoes (and let’s face it, there are lots of new tomatoes – we test WAY too many in the AAS process for my liking). The board of AAS judges reads the entry info from the new cultivar being tested and selects plants (usually two) to compare it against. If the trial is a yellow cherry tomato, it will be grown and tested alongside other yellow cherry tomatoes. The scoring is based on whether its performance or taste is as good as or better than the comparisons. If most judges don’t rank it as “better” then it has no chance of winning.

Confidentiality and Proprietary Plants

The fact that the testing is blind, paired with the fact that results of “failed” tests are not released, lends itself to confidentiality. Another important factor about the testing is the proprietary nature of the tests and test sites. These are new plants that haven’t been introduced to the market (except for the case of perennial trials) and are usually for proprietary or patented plants. Test sites should have some sort of control over who enters them and signs prohibiting the collection of seeds, pollen, or cuttings are placed at the site. Believe it or not, the world of plant introductions can be dog-eat-dog and cutthroat.

So what if it doesn’t win?

One of the cool things about the test is seeing the announcements of the winners early the following year. You see the list of plants and think back to what you grew the previous season. If often find myself thinking “oh yeah, I remember that plant, it did really well” and sometimes even “how did that win, it did horrible for me.” This is a good reminder that we can’t base generalized garden recommendations on anecdotal evidence. What did well for me may not work for someone else and vice versa. All the results from the test sites go together to provide a general view of the plant performance. It will do well for some and not others.

So if most of the judges rank the crop as not performing, looking, or tasting as good as the comparisons the plant doesn’t win. And that’s it. Due to the confidential nature of the testing you won’t know that it failed the test. Even I won’t know that it failed the test. It will likely go on to market without the AAS seal where it will face an even tougher test – the test of consumer demand. Of course, many people may grow it and be successful, and some may grow it without success.

What are the AAS Winners and how do I find them?

There’s a list of plants announced each year through the AAS website and social media channels. You can find a list, in reverse order of winning (meaning most recent first) on the AAS Website. The site also has a searchable database if you’re looking for a specific plant. Since these plants are owned by lots of different seed companies and breeders, there’s also a retailer listing on the site. The AAS program also supports a number of Display Gardens across the country, including botanical gardens, university gardens, and others where the public can see the most recent winners growing. Here in Omaha we maintain a display garden for the ornamental plants at our county fairgrounds. We also have our on-campus garden which is used for our TV show Backyard Farmer (the longest running educational TV program in the country, BTW) which serves as a display garden for both ornamental and edible crops.

I recently shared the AAS Testing Program with the local news here in Omaha. Check it out:

Some of my favorite recent AAS Winners
Asian Delight Pak Choi – this was planted in May and didn’t bolt. We were still harvesting it in October.

Pepper Just Sweet – these plants were big and healthy even when everything else was struggling. The peppers were delicious.

Potato Clancy – potatoes….from seed! Just fun!

Pepper Habanero Roulette – All of the fruity sweet, none of the heat. A fun heatless habanero.

Dianthus Intraspecific Supra Pink– A reblooming, prolific Dianthus with interesting ruffled flowers.

Eggplant Patio Baby – container sized eggplant with mini fruits perfect for cooking or roasting whole.

Ornamental Pepper Black Pearl – Cute purple flowers lead to these shiny pepper pearls. Love the black leaves, too.

To Fertilize, or Not to Fertilize, that is the question

You see a bright shiny package at the garden center saying that it can help you have the most bountiful garden ever, the greenest lawn in the neighborhood, your plants will have miraculous growth, or it will supply every element on earth to make sure that your plants are living their best life. It’s got what plants crave….It’s got electrolytes! You reach out to grab that package and ……. Woah! Pump the brakes! Do you know if your plants even need to be fertilized? Are you just falling for that shiny marketing, or do your plants really need added fertility to grow?

It turns out that many gardeners add fertilizer out of habit or because a shiny package or advertisement told them they needed to do it. The fact is, though, that you may or may not need to add fertilizer to get your plants to grow healthy. It is actually more likely than not that the level of nutrients in soil is perfectly adequate for healthy plant growth. And guess what, there really is a way to know what plants crave…or at least are lacking: A soil test.

We here at the Garden Professors (and those of us who work in extension) often get questions or hear comments about gardeners adding fertilizer or random household chemicals and items to their plants and soils with no idea what they do or even supply. They’ll throw on the high powered 10-10-10, the water soluble fertilizer, rusty nails, or even (shudder) the oft mentioned Epsom salts because it is just what they’ve been told to do.

A few months ago, my GP colleague Jim Downer talked about why to amend soil– focusing mainly on organic material and a little bit of fertility. In this article, I’m going to share some how and what: what plants need in terms of nutrients, how to determine what nutrients you need to add, what you can use for increasing fertility (conventional and organic), and how to calculate how much fertilizer to add.

What plants really need

Plants have a number of essential plant nutrients that they need from the environment in order to properly grow and function. Hydrogen, carbon and oxygen are all important, but are not something that gardeners have to supply since they are taken in by the plant in the form of water and carbon dioxide (unless you forget to water your plants, like I sometimes do — but death will occur from dehydration well before lack of hydrogen).

There are six soil macronutrients, which means that they are used in larger amounts by the plants. These include nitrogen, phosphorous, and potassium, which form the basis of most common fertilizers that have those magic three numbers on them (example: 10-10-10). Those three numbers indicate that the fertilizer contains that percentage of the elemental nutrient in it. For this example, the fertilizer contains 10 percent nitrogen, 10 percent phosphorous, and 10 percent potassium. The other three soil macronutrients are magnesium, sulfur, and calcium. Depending on your location, your soil may be abundant or deficient in these nutrients, especially magnesium and calcium. Sulfur is commonly released during decomposition of organic matter, so it is usually present in sufficient amounts when soil is amended with (or naturally contains) organic matter.

If a soil is deficient in a nutrient that a plant requires it is usually a macronutrient since plants use them at higher levels. However, deficiency is still unlikely in most soils unless there is a high volume of growth and removal, such as in vegetable gardens and annual beds (or if you’re growing acres of field crops like they do here in Nebraska). These are also the nutrients that are most common on soil tests, since they are the ones that are used the most by plants.

Soil micronutrients are needed in much smaller amounts. Those nutrients are boron, copper, chlorine, manganese, molybdenum, and zinc (remember the periodic table?). These are also usually supplied from organic matter or from the parent soil material so deficiency is even less likely than for macronutrients. Tests for these aren’t usually part of a basic soil test, so if you suspect you might have a deficiency you might have to get a specialized test. There are some basic physiological signs of deficiency that plants might exhibit in response to specific deficiencies, but their similarity to other conditions make it an imprecise tool for diagnosing a deficiency.

Compost is a good source of nutrients, especially micronutrients (as we’ll read later). Using compost alone may be sufficient for many gardens, such as perennial beds. However, higher turnover and higher need areas like vegetable gardens may need supplemental fertilization beyond compost. That’s where the soil test comes in.

What’s on the menu….interpreting soil test results

If you’ve had your soil tested by a lab (which is recommended, since it is much more precise than those DIY test kits), you’ll get results back that give you the level of nutrients in your soil and usually recommendations for how much of each nutrient you need to add to the soil for basic plant health. This is a general recommendation that is common for most plants, which is generally sufficient for average growth. If the test says that the nutrient levels are normal, you don’t have to add anything….I repeat….YOU DON’T HAVE TO ADD ANYTHING. If it says you need one nutrient of the other you’ll need to add it to your garden or around the plant. As we’ve said before, disturbing the soil as little as possible is best, so if you’re using a fertilizer product aim for one that you can broadcast on top of the soil or is water soluble. This goes for compost as well – try to apply it to the top of the soil and it will incorporate over time.

Your soil test results will usually tell you to add nutrients in pounds per a certain square footage. In the example pictured, there’s a recommendation of 3.44 lbs of Nitrogen per 1000 square feet. That number is for the actual nitrogen, and since different nutrient sources have different amounts of nitrogen you’re going to have to do some math to figure out how much fertilizer you need per 1000 square feet and then multiply that by how many thousands of square feet you have.

I’ll note here that soil labs do not usually test for nitrogen due to the variable nature of nitrogen in the soil and the lack of affordable or reliable tests. Nitrogen fluctuates widely over a short period of time and is not as persistent in the soil as other elements due to plant take-up, microbial action, and weather conditions. Nitrogen recommendations are usually made based on the crop indicated for the test and may be informed by the levels of other nutrients.

Let’s say that I’m using an organic fertilizer product I purchased at the garden center and the nutrient analysis is 4-3-3 (these numbers are standard for organic nutrient sources, which have lower nutrient levels than conventional fertilizers). That means that for every 100 lbs of that product, 4lbs are nitrogen, 3 are phosphorous, and 3 are potassium. My (hypothetical) garden is 10ft by 20ft, which is 200 square feet.

So we divide 200 by 1000 to get .2, which represents that my area is 20% of the area listed on the recommendation. If my garden were 3500 square feet, then that number would be 3.5.

Next, multiply the Nitrogen recommendation of 3.44 lbs by .2. This give me 0.688. This tells me that I need .688 lbs of nitrogen to amend my 200 square feet.

So I just need to weigh out .688 lbs of the fertilizer, right? Nope – we have to account for the fact that my fertilizer is only 4% nitrogen- only 4 lbs out the 100 lb bag. We can estimate amounts by figuring out how much nitrogen is in smaller amounts of the fertilizer. Since we know that 100lbs has 4lbs of N, then 50lbs has 2lbs of N, and 25lbs has 1lb of N. If I want to get a more precise amount of fertilizer poundage to get my .688 lbs of N, then we divide the pounds of N needed by the decimal percentage of N in the fertilizer. So that would be .688 / .04, which gives us 17.2 lbs of fertilizer.

Now, considering that the bagged product that I bought is $25 for 8lbs, I may want to reconsider using it for this application…unless I enjoy throwing my pearls before swine or I’m fertilizing my money tree.

If you do the math, you’ll note that this fertilizer will add more than the recommended amount of phosphorus and potassium. You’ll either need to decide if that is acceptable or if you need to find another source of nutrients.

If you’re not using a prepared fertilizer product but rather an organic source of nutrients, you can still calculate how much to add to get to the recommended amount. The following are some good lists of nutrient ranges of organic materials:

https://extension.psu.edu/using-organic-nutrient-sources

https://vegetableguide.usu.edu/production/soil-nutrient-water-management/organic-nutrient-sources

A note about pH

Another thing your soil test will tell you is the pH of the soil. In general, plants prefer a soil pH just on the acidic side of neutral (between 6.0 and 7.0). There are plants that prefer different pH levels – such as blueberries and azaleas and their need for a more acidic soil between 4.5 and 5.2. Changes in pH affect the availability of nutrients to plant by affecting ionic bonds of the elements. For the most part, the nutrients are more available at that neutral pH. You’ll note that iron is more available at lower pH levels, which is why those acid-loving plants grow better at lower pHs – they’re heavier iron feeders.

If your pH is extreme in one way or the other, you’ll either need to find plants that thrive at that level or adjust the pH if that isn’t possible. To raise pH in acidic soils the most common method is application of lime. To lower pH, you’ll need something high in sulfur. For more information, visit https://articles.extension.org/pages/13064/soil-ph-modification .

Having a philosophical moment in the garden

Ripe for the picking: Which fruits keep ripening after harvest?

“Will my peppers continue to ripen? How about my eggplants?” It is common knowledge to most gardeners (and home cooks) that tomatoes will ripen on the kitchen counter, as will bananas and several other fruits. You know that one day your bananas look perfectly ripe and the next they’re a brown mush But does this work for all fruits? We often get questions about whether specific fruits will continue to ripen after picking. And the answer is….. it depends.

One of these fruits is not like the other

The answer as to whether a fruit will continue to ripen after harvest depends on which one of two groups it falls into. These groups are climacteric and non-climacteric fruits. In short, climacteric fruits are the ones that will continue ripening after harvest and non-climacteric fruits are ones that don’t ripen after harvest.

This refers to the “climacteric phase” of fruit ripening where there is an increase in the gaseous plant hormone ethylene and an increase in respiration, which drives the ripening process. It is the climacteric fruits that will keep ripening once they’ve been harvested, thanks to ethylene. The only stage of maturity for non-climacteric fruits after harvest is…..compost.

As long as you’re green, you’re growing. As soon as you’re ripe, you start to rot. -Ray Kroc

Almost all fruits produce ethylene, but non-climacteric fruits produce them at much lower levels and do not rely upon it as the main driver of ripening. I’ll go into a bit more detail in a bit, but first – which fruits are climacteric and which are non-climacteric?

Common Climacteric Fruits	Common Non-Climacteric Fruits
Apple	Brambles (raspberry, blackberry, etc).
Apricot	Citrus (oranges, lemons, limes, etc.)
Avocado	Eggplant
Banana	Grape
Blueberry	Melon (including Watermelon)
Cantaloupe / Muskmelon	Pepper *
Cherry	Pumpkin
Fig	Squash (summer and winter)
Kiwi	Strawberry
Mango	Cherry
Papaya
Pawpaw
Peach
Pear
Plantain
Plum
Tomato

*Some evidence of climacteric ripening in hot peppers

The ripening process

Ripening is genetically programmed – meaning that it is highly dependent on processes that are regulated by genes and it specific to each species. Parts of the process are started and stopped due to the transcription and translation of genes, which are in turn controlled by signals such as chemical compounds, physiological stages of the plant, climate, and so on. These ripening processes have a lot of end results – sugars accumulate in the fruit, pigments develop, some compounds that have pleasant flavors develop while others that are unpleasant are broken down, some of the pectins in the fruit break down to make it softer, and on and on.

Tomatoes – the classic climacteric fruit

Research shows that ethylene, the simple little gaseous hormone plays a crucial role in the ripening of climacteric fruits by altering the transcription and translation of genes responsible for ripening. Ethylene is the dominant trigger for ripening in these plants. Ethylene receptors in the cells are triggered by the presence of the gas which leads to cascade effect. This is why ethylene can be introduced from other fruits to trigger ripening in fruits that aren’t ready to ripen. If you’ve heard of the tip to put an apple in a bag full of some other fruit to get it to ripen, it actually works – as long as it is a climacteric fruit.

The same ripening processes happen in non-climacteric fruit as well, but they are not dependent on the presence of ethylene. In fact, these pathways are also present in climacteric fruits – the ethylene-dependent processes are just the dominant (and faster) way that they ripen.

Controlling ripening

The dependence on ethylene for a vast majority of fruits to ripen has been used by farmers and the food industry for a long time to keep climacteric fruit more stable for shipping. These fruits are harvested “green” before they ripen and shipped unripe since they are much firmer and much less likely to get damaged in transit. These days, bananas, tomatoes, and other climacteric fruits are likely to be given a treatment that temporarily inhibits the ethylene response before harvest or shipping to extend their shelf life further. Once they’re close to their final destinations they’ll either be allowed to ripen on their own or given a treatment of ethylene to speed back up the ripening process.

What we gain in shelf-life and reduced food waste we do lose in a bit of flavor. Since the fruits are no longer attached to the plant when they ripen they don’t have the chance to transport more sugars and flavor compounds from the mother plant. So “vine ripened” fruits do have a bit more sweetness and flavor than those that are picked green. Having just gotten back from Rwanda, a country where bananas are a common staple food I can attest that the ones that ripen on the plant are much sweeter than those we get shipped in to the US – you know, the ones that will ripen next week sometime if you’re lucky. There were even some in our group that don’t care for bananas here that loved the ones we had at breakfast every morning.

One possible direction for biotechnology is the engineering of plants to alter or eliminate the ethylene ripening response to reduce food waste and spoilage. Since many genes that are responsible for ethylene production such as enzymes that catalyze the production of ethylene precursors, or proteins that serve as ethylene receptors have been identified, work is being done to develop delayed ripening by altering or knocking out these genes in a variety of crops.

Sources

Alexander, L., & Grierson, D. (2002). Ethylene biosynthesis and action in tomato: a model for climacteric fruit ripening. Journal of experimental botany, 53(377), 2039-2055.

Pech, J. C., Bouzayen, M., & Latché, A. (2008). Climacteric fruit ripening: ethylene-dependent and independent regulation of ripening pathways in melon fruit. Plant Science, 175(1-2), 114-120.

Lelièvre, J. M., Latchè, A., Jones, B., Bouzayen, M., & Pech, J. C. (1997). Ethylene and fruit ripening. Physiologia plantarum, 101(4), 727-739.

Plant Control to Major Tom(ato): The Art of Spacing Out Your Plants

“Why don’t you just plant it up against the house,” piped my mother-in-law. She was talking about a run-of-the-mill “old fashioned lilac” that we had received in the mail for our donation to Arbor Day. While I don’t necessarily think of the organized tn as a source of high-quality or novel plants, I felt beholden to make a donation since it was founded and is still located in Nebraska (and we have visited the Arbor Lodge, home to founder J. Sterling Morton and his brood of tycoons (one of salt fame – that Morton, one of cornstarch fame – ergo we have Argo, and one of the railroad). I had pawned the 10 blue spruce off to the freebie table at the office, but she wanted a lilac…and what momma-in-law wants, momma-in-law gets.

I explained to her that the labeled final size of the cultivar was 12 feet in diameter, so it needed to be at least 6 feet from the house (preferably more) and from other plants. “Nonsense!” she decried, “I planted mine close to the house. You just have to keep it pruned back. Mine did just fine….. until it rotted.” Since the right spacing would put the shrub in the middle of a narrow passage between the house and the fence, I opted to throw it into a pot since I was heading out of the country the next day for two weeks. It was, after all, a little more than a spindly twig (with roots wrapped together in a ball) sheathed in plastic.

What’s the issue?

Most gardener’s desire for instant gratification often means that correct spacing for the finished size of the plant gets thrown out the window so that the garden looks good to go from the beginning. Or even worse, plants get shoved against houses, under power lines, or in other areas where they’ll either be cramped and crowded or incessantly pruned to the point of oblivion throughout their probably shorter-than-expected lifespan. Think of it like your bubble of personal space. Just like you don’t want to be crowded, neither do plants.

In addition to the pruning and space issues, crowding can increase the likelihood of disease or other plant issues. Crowded plants reduce air flow, which aids the development of diseases by increasing (ever so slightly) the humidity in the plant’s microclimate, increasing drying times after rain or irrigation, and even allowing for disease spores to more easily settle on the plants. For perennials, and especially trees and shrubs, overcrowding can be a chronic issue since the problem can last for many, many years.

That’s not to say that spacing it isn’t a problem with annuals, either, especially in the vegetable garden. In addition to the increased possibility of disease, competition for space and for nutrients can reduce yields. Crowded root crops like carrots, beets, and radishes don’t have enough space to fill out, resulting in stunted and irregular produce. The same goes for leafy crops like lettuce or kale. Fruiting crops like tomatoes and peppers can also suffer from reduced production when plants can’t fully grow to their potential.

Getting Spacing Right: The Simple Art of Not Planting Too Damn Close

Perhaps the secret is complicated formula for figuring out the proper plant spacing? Or perhaps it is some specific planetary alignment you need to wait for? Since it seems to mystify may gardeners, spacing must be difficult, right? Au contrare!

Most plants come with the proper space printed right on the label! Think of such a novelty! That lilac my MIL wanted to plant against the house said right on the packaging that it generally grew to 12’ wide. If I were planting a bunch of them in a row (and not as a hedge), I could plant them 12’ apart. If I wanted to grow them as a hedge, I’d reduce that spacing to make them grow into each other (but it will take time for them to grow into a hedge…so they won’t be touching right away). Keep in mind that this is the genetic potential of the plant and isn’t a guarantee. Many factors, including microclimate, soil conditions, precipitation, nutrient availability, disease, etc. etc. etc. could limit the plant’s growth to that potential (or even more rarely increase it). What if I’m not planting a bunch in a row? Here’s were a teensy bit of math comes into play.

Think of plants in general terms as circles. Just look at a basic landscape architect’s plans and you’ll sometimes see plants represented generally as circles. If you think all the way back to that geometry class in high school, you’ll remember that there are several measures of a circle, including the diameter and the radius. The diameter is the width of the circle from one side to the other. The radius is the distance from the center point of the circle to the edge. So if our plant is a circle, then the listed width of the plant is the diameter and the distance from the trunk, stem, or center is the radius. So I can expect my lilac (if it reaches full potential) to grow out 6 feet from the trunk. That means I need to plant it at least 6 feet away from the wall. If I wanted to plant it in the landscape with other plants around it, I would need to figure out the radius of the plants I wanted to plant close to it and add their radius to the lilac radius to figure the minimum distance I should plant them apart. Let’s say I wanted to plant a small shrub beside the lilac with listed width of 10 feet. That means the radius of that shrub is 5 feet. Adding them together, I get a distance of 11 feet. On the other side of the lilac I want to plant a large perennial with a diameter of 4 feet. The radius would be 2 feet, so my minimum planting distance would be 8 feet. You also have to keep in mind any variation due to microclimate and environmental factors.

What about the vegetable garden?

The same concept holds true for the vegetable garden as well – think of each of the plants as a circle. Where planning the spacing is different is usually interpreting what the seed packet says in terms of in-row versus between-row spacing. The in-row spacing is based on the size of the plant, a general idea of the size of the circle the plant makes or how much space it needs between plants (some plants, like beans, are OK when they overlap a bit and share space). The between-row spacing is for human use in creating typical in-ground, large garden areas. I’ve had the discussion before of large garden area vs. in-ground beds, vs. raised beds so we don’t need to go into that detail, but the general movement is toward some sort of bed system to reduce walkways (reducing bare soil that can lead to erosion or compaction when walked on) and intensify plant spacing/output per a given area.

Taking that into consideration, use the in-row spacing as the between plant spacing in all directions. This is what the popular Square Foot Gardening method does – the spacings and number of plants per square are based on the between plant spacing and eliminates row spacing. For example, radishes and carrots typically have an in-row or between plant spacing of 3 inches. If you fit that spacing evenly within a foot row segment, you get four plants. When you make that two dimensional you get 16 plants per square foot. For four inch spacing you get 3 per foot and 9 per square foot, six inch spacing you get two and four, etc. You can fill an entire bed with plants like this without spacing between rows of plants.

Of course, the tricky thing is that, just like our trees and shrubs that are planted too closely reduced airflow and increased microclimate humidity can increase the risk of diseases in the plants. The Square Foot Gardening method by the book states that you shouldn’t plant any adjacent square with the same crop to decrease likelihood of disease sharing, but that seems sounder in theory than in practicality. I use some of the spacing (and you don’t need the book, just look at the between plant spacing and calculate. You just have to monitor, use good IPM, and treat or remove issues promptly to reduce disease issues. Using interplanting to intensively plant by mixing various space usages (tall plants with short plants, root crops with fruit crops) can also help make use of the space while mixing plants to reduce disease spread.

The Scoop on Poop: Manure in the Vegetable Garden (and potential food safety risks)

“Can I use manure to fertilize my garden?” That’s a common question we get in Extension and on the Garden Professors page. The answer is absolutely, but there’s a “but” that should follow that answer that not everyone shares. And that is…but for fruits and vegetable gardens the manure you apply could be a potential source of human pathogens that could make you or your family sick. There are procedures and waiting periods you should follow to reduce the potential risk to human health from pathogens in manure and other animal products.”

Why manure?

First, application of manures to garden and farm production spaces is a good use of nutrients and provides a way to manage those nutrients to the benefit of growers and the environment. Using the concentrated nutrients in the manures to grow crops reduces what washed downstream in the form of pollution. In addition to adding nutrients to the soil, application of manure and other animal byproducts (bone meal and blood meal, for example) add organic matter to the soil, which improves soil texture, nutrient retention and release, and supports beneficial microorganisms.

Typical N-P-K composition for some manures and composts. Source: UC Davis

For organic production, both in home gardens and on farms (certified organic or not), manure and animal products are an important input for fertility. For the most part, manures offer a more concentrated (higher percentage) of nutrients by weight than composts composed only of plant residues, so less is usually needed (by weight) than plant composts to apply the same amount of nutrients.

While the nutrient levels of manures and composts can be highly variable, there are some general ranges that you can use to plan your application based on the needs you find in your soil test. (And you should be doing a soil test, rather than just applying manure or compost willy-nilly. Just because the nutrient concentrations are lower than a bag of 10-10-10, you can still over-apply nutrients with composts and manures).

So what are the hazards?

As you’ve probably realized from bathroom signs and handwashing campaigns, fecal material can carry a number of different human pathogens such as E. coli and Salmonella. The major risk around application of manures to edible crops is the possible cross-contamination of the crop with those pathogens. The number one hazard leading to foodborne illness from fresh produce is the application of organic fertilizers – mainly manure, but also those other byproducts like blood meal and bone meal. Add in the fact that the consumption of raw fruits and vegetables has increased over the last decade or more, and you’ll soon understand why Farmers who grow edible crops must follow certain guidelines outlined in the Food Safety Modernization Act (FSMA, which you’ll hear pronounced to as fizz-mah) to reduce the potential risk that these pathogens pose to people who eat the crops. Right now, only farms with a large volume of sales are required to follow the guidelines, but smaller producers are encouraged to follow them as best practice to reduce risk and liability. And while there isn’t a requirement for home gardeners to follow the guidelines, it is a good idea to understand the risks and incorporate the guidelines as best practice. It is especially a good idea if the produce is being eaten by individuals who are at higher risk of foodborne illness – young children, the elderly, or those who are immunocomprimised.

The recommendations are also suggested when there’s contamination from unexpected or unknown sources like when vegetable gardens are flooded (click here for a recent article I wrote to distribute after the flooding in Nebraska and other midwestern states).

Recommendations to reduce risk

As previously stated, while these recommendations have been developed for produce farmers, research showing the potential hazards of applying manures means that it is a good idea for home gardeners to understand and reduce risks from their own home gardens.

The set of guidelines outlined by FSMA cover what are called Biological Soil Amendments of Animal Origin (BSAAO – since we government types love our acronyms). Here’s the “official definitions” used in the rules for produce farming:

A Biological Soil Amendment is “any soil amendment containing biological materials such as stabilized compost, manure, non-fecal animal byproducts, peat moss, pre-consumer vegetative waste, sewage sludge biosolids, table waste, agricultural tea, or yard trimmings, alone or in combination”.

A Biological Soil Amendment of Animal Origin is “untreated: cattle manure; poultry litter; swine slurry; or horse manure.”

Image result for manure — Now that’s a pile of crap!

For BSAAO (we’ll call it raw manure), manure should only be applied to the soil and care should be taken not to get it on the plants. There’s also a waiting period between applying the manure and when you should harvest the crop. The length of the waiting period depends on whether the edible part of the crop comes in direct contact with the soil. Right now the USDA is still researching the appropriate waiting period between application and harvest, so the general recommendation until then is to follow the standards laid out in the National Organic Program (NOP) standards. Research shows that while pathogens may break down when exposed to the elements like sun and rain, they can persist for a long time especially in the soil.

For now, here are the recommendations:

For crops that contact the soil, like leafy greens (ex: lettuce, spinach, squash, cucumbers, strawberries) the suggested minimum waiting period between manure application and harvest is 120 days.

For crops that do not contact the soil (ex: staked tomatoes, eggplant, corn) the suggested minimum waiting period between manure application and harvest is 90 days.

For farmers following FSMA, the waiting periods could change when the final rule is released – some early thoughts are that it could increase to 9 – 12 months if the research shows a longer period is needed.

What about composted manure? Is it safe? The guidelines indicate that there isn’t a waiting period between application of manure that has been “processed to completion to adequately reduce microorganisms of public health significance.” But what does that mean? The guidelines lay out that for open pile or windrow composting the compost must be maintained between 131°F and 170°F for a minimum of 15 days, must be turned at least 5 times in that period, must be cured for a minimum of 45 days, and must be kept in a location where it can’t be contaminated with pathogens again (animal droppings, etc). Farmers have the added step of monitoring and thoroughly documenting all of the steps and temperatures. Now we know that that’s a bit of overkill for home gardeners, but suffice it to say that the cow manure that’s been piled up to age for a few years that you got from the farm down the road doesn’t meet that standard.

Image result for compost — Failure to maintain proper temperature on composted manure could mean that your goose is cooked, though this thermometer doesn’t have that setting.

“Aged” manure ≠ “processed to completion to adequately reduce microorganisms of public health significance.” So unless you know for sure that you’ve reached and sustained the appropriate temperatures in your compost, you should assume that it would be considered a BSAAO subject to the 90/120 waiting period. Bagged manure you buy at the garden center is likely to be composted “to completion” or may even have other steps to reduce pathogens like pasteurization. Sometimes the label will indicate what steps have been taken to reduce pathogens, or even state that it has been tested for pathogens.

The recommendations also specifically mention compost teas and leachates (a topic we handle with much frequency and derision here at the GPs, since there’s not much science to back up their use and I mention here with much trepidation). For the sake of food safety, any tea or leachate should only be applied to the soil, not the plant. And for home compost that doesn’t even contain animal manure the 90/120 day waiting period should still be observed in most cases since some of what goes into home compost is post-consumer. Since we put pieces of produce in there that we’ve bitten from or chewed on (post-consumer), plus some animal origin items (eggshells) there’s the potential that we could contaminate the compost with our own pathogens – and the environment is perfect for them to multiply.

The Bottom Line

While these guidelines and rules for farmers may just be best practice recommendations that we can pass on to home gardeners, common sense tells us that taking precautions when applying potential pathogens to our edible gardens. An ounce of prevention is worth a pound of cure, especially when were talking about poop.

Sources/Resources:

Produce Safety Alliance producer training materials
National Good Agricultural Practices Program: Soil Amendments (Cornell)
Biological Soil Amendments of Animal Origin (FDA Fact Sheet)
FSMA Final Rule on Produce Safety (FDA)
Manure in Organic Production Systems (ATTRA)

Supplemental Lights for Home Seed Starting and Indoor Growing: Some Considerations

Whether you’ve already got seedlings growing away or getting ready to start your annual indoor seed starting, one of the important factors in seed starting is light. (Last month I covered heat, which you can see here). Questions like “Do I need to use supplemental light or can I use a window?” and “What kind of light do I need to use?” are ones we often get from gardeners – new and seasoned alike. So I thought I’d take a little time to talk about light – the factors that are important for plant growth some ways that you can make sure you’re providing the right kinds and amounts of light to your new seedlings. Keeping these ideas in mind can help you choose lights for your seeds starting (or other plant needs), whether it is a simple shop light ballast from the hardware store, a pre-fab light cart system, or even higher-tech LED system.

Plants require light for several of their functions, most importantly the process of photosynthesis. The green pigments in plants (Chlorophyll A and B) act as receptors, gathering electrons from the light to use as an energy source to manufacture glucose, which is stored in the plant in a number of ways and then ultimately broken down in respiration to release energy to support plant functions. There are three aspects to light that gardeners should keep in mind for supplemental lighting: quality (color), quantity (brightness/intensity), and duration (day/night length).

Duration is a relatively simple concept when it comes to seeds starting and light set-ups. Gardeners will want to try to mimic the natural environment that will be provided by the sun. For the most part, aiming for 16 hours of light and 8 hours of dark is standard. This gives the plant sufficient light, but also provides a rest period which can be important for plant functions. Most gardeners find it handy to invest in timers to turn lights on and off, rather than trying to remember to do it themselves. This can be a simple on-off set up from the hardware store (after-holiday shopping can be a good way to pick them up on sale in the string light section) to something more elaborate from grower suppliers. Duration could be more important if you’re doing longer term growing beyond seeds starting, as day length affects initiating of flowering in some plants.

Intensity refers to how bright the lights are. Some lucky people have big windows with lots of bright light for starting seeds, but even for them intensity (and duration) may not be enough during the shorter, grayer days of winter. Growing in bright windows can sometimes be a challenge because the light is coming from the side rather than above, so plants often grow toward the window and need to be rotated. Supplemental light can increase intensity and lengthen duration, even for plants grown in windows.

Most commonly, light bulbs are sold by wattage as a measure of their energy (light) output. Standard tube florescent lights are generally around the 40 Watt level, but some of the full spectrum plant lights come in 54W options. If you can find it, the higher wattage can make a big difference in the intensity of light and thus the production of your plants. Even at the higher wattage, you’ll want to get a ballast that holds at least two bulbs (and some grow light ballasts hold more). You can further control the intensity of light reaching your plants by increasing or decreasing the distance between the plants and the lights. This is why the pre-made plant carts have a chain or other mechanism for you to raise and lower the lamps. For fluorescents, lights are sometimes lowered to around an inch above the canopy of the plants. For high intensity LEDs, the distance may need to be more. (If you’re using lights for long-term growth of, say houseplants, you’ll have to experiment with the distance to meet the intensity needs of the plants – closer for high light plants and farther away for low light plants).

Light Quality: The Rainbow Connection

Sunlight, or white light, is composed of all of the colors of the spectrum. Think back to art class and our friend ROY G BIV – the colors of the rainbow. There’s also parts of the spectrum that we don’t see like ultraviolet and infrared. For photosynthesis, plants mostly use light in the red and blue spectrum (referred to as Photosynthetic Active Radiation, or PAR), though almost all of the colors have some sort of effect or function on plants. Blue light has a role in promoting vegetative growth in plants, while red has a role in promoting flowering.

For most applications, supplemental light for seed starting or other indoor growing should be full-spectrum. You can achieve this in a variety of ways – buying specific full-spectrum plant light bulbs is the best, but you can buy non-plant specific full spectrum bulbs as well. For small-scale home growers and beginners, it can be as simple as buying a shop light ballast at the hardware/box store with a full spectrum bulb. For more intensive or large-scale growers, there are lots of sources for higher-end, full spectrum grow lights that you can buy from specialty garden retailers, but these are often more than what home gardeners starting seeds indoors need.

Fluorescent vs LED

Image result for fluorescent shop light — Typical shop light ballast

These days you might be presented with a choice of lights – fluorescent vs. LED. There are some positives and negatives to each. While they have a higher up-front cost, LEDs use much less energy than fluorescents and can save money over several seasons of use. The reduced energy usage also means there’s less energy loss in the form of heat, which can be a positive if you are always struggling with creating excess heat that burns your plants, but a negative if you’re relying on that heat to help keep the temperatures up (see my article from last month on heat and seed starting) or have issues with drying out your growing media. Fluorescents on the other hand can be more affordable up-front, but have a higher energy usage that will result in higher electric bills over time.

understanding the basics of grow lights for indoor plants and indoor gardening — LED grow light via Shutterstock by nikkytok

You might have noticed in your searching or in visiting some growers that LED lights for plant growth come in either white (full spectrum) or a red/blue combination which end up giving a purple light. Since LEDs give a larger control over the spectrum of light, growers, especially larger scale intensive operations, use these red/blue combinations as a means to add further energy efficiency since it is the blue and red spectra that are the photosynthetic. By eliminating the spectra that are largely reflected rather than absorbed, less energy is used. This is useful in hydroponic and vertical farming systems where short-term crops are being grown quickly and where profit margins can be slim.

You can read (and listen to) more about light in the Joe Gardener podcast and article on seeds starting I was interviewed for last year with Joe Lamp’l.

However, research has emerged in the last few years that expanding the spectra of light in LED systems increases production. Research has shown that incorporating green LEDs significantly increases production over just red/blue LEDs (some of that research was by Kevin Folta, who is one of the leading science communicators on biotechnology). While green plants largely reflect rather than absorb green light, it does have some effect on plant functions. (Research also shows that adding the green makes the light appear a little more natural to workers in facilities like greenhouses and makes it easier to see issues with the plants – the purple of the red/blue systems washes out the plants and makes it hard to see differences in leaves like diseases).

So if you’re looking at LEDs for seeds starting, and especially if you’re looking at them for longer term indoor plant growing, stick with full spectrum or explore one of the LED systems that incorporates green. Though don’t be afraid to experiment with the colorful LED options – I have a small red/blue system to supplement light to my office potted lime. The key is to experiment and shop around – every gardener’s need for supplemental light is different and the solutions to those needs are different. Don’t be afraid to start small with that shop light from the hardware store before working your way up – especially if you’re just starting a small amount of seeds in the spring.

Feel the Heat: Temperature and Germination

In most parts of the country it is time to dust off the seed starting trays, pick out your favorite seeds, and get a little plant propagation going on. There’s definitely a lot of science (and perhaps a bit of art) to successful seed starting. While the process starts (and relies on) the imbibition of water, one of the biggest factors that affects the success, efficiency, and speed of seed germination and propagation is temperature. Germination relies on a number of chemical and physical reactions within the seed, and the speed and success of those reactions is highly temperature dependent. Respiration, where the seed breaks down stored carbohydrates for energy, is probably the most notable process involved that is temperature dependent (source). Think of it in terms of a chemical reaction you might have done back in your high school or college chemistry class – there’s an optimum temperature for the reaction and any lower and higher the reaction might slow down or not happen at all.

Thinking of it this way, seeds and germination are just like Goldilocks and her porridge – there’s too hot, too cold, and “just” right. Seeds are the same way – there’s a “just right” temperature for germination. The seeds of each species has a different optimal temperature for germination with a range of minimum and maximum temperatures for the process.

Why is important that seeds are started at their optimal temperature?

The optimal temperature is the one at which germination is the fastest. This may seem to only have consequences for impatient gardeners, but slower germination speeds increase the days to emergence for the seeds, which in turns means that the seeds and seedlings have a greater chance of failure. The early stages of germination are when seedlings are most susceptible to damping off, which can be caused by a number of fungal pathogens (Fusarium spp., Phytophthera spp., Pythium spp., etc.) that basically cause the seedling to rot at the soil level. These pathogens (as well as decomposers in some cases) can cause seeds to rot or decompose before emerging as well. That’s why you’ll sometimes see seeds that are slow to germinate (or traditionally direct sown like corn, beans, and peas) treated with those colorful fungicides. The fungicide gives the seed and seedling a little bit of protection (for a week or so, depending on the product), which is handy if you accidentally sow them before soil temperatures are optimal or if the species is slow to germinate.

If emergence is really slow, there’s also the possibility of stunting or failure due to exhaustion of the stored carbohydrates that the seed relies on until it begins photosynthesis. So the closer to the optimal temperature the seed is, the faster the emergence and the highest percentage of germination success.

What does this mean for home gardeners?

Whether you are starting seeds indoors or direct sowing outdoors, knowing the germination temps can help increase your likelihood of success. You can find a variety of resources for the optimal germination temperature for your selected crops. In general, most warm season plants, like tomatoes, peppers, and summer flowers are in the 70-80 °F range. This is why most of the warm season crops are started indoors – so temperatures can be controlled to higher levels.

For vegetable crops, here’s a good resource for basic germination temperatures. And here’s one for a few annual flowers.

Many of the cool season crops germinate at much lower temperatures, which means many of them can be directly sown early in the season rather than started indoors. Crops such as spinach, lettuce, and other leafy greens have these lower germination temps and typically perform better if germinated at lower temps.

Germinating a variety of plants for our 2018 All-America Selections trials

It should be noted that this is for the soil temperature, not the air temperature. If you’re starting seeds in your home, most people don’t keep their homes in the 75 – 80 degree range in the winter. Many commercial operations use warmed tables or beds for seed starting, rather than heating the whole facility to the necessary temp – it would be expensive. For home growers, supplemental heat mats can help increase soil temp without having to heat a whole room. In a pinch, you can even clean off the top of your fridge and keep seedlings there. It is higher up in the room (heat rises) and most refrigerators create some amount of external heat as they run.

For any seeds that you’re direct sowing outdoors, whether they require higher or lower germination temperatures, you’ll have more success if you plan your sowing around soil temperatures rather than calendar dates (planting calendars can be good for estimation, though). Investing in a soil thermometer can offer detailed information on the specific temperatures in your garden soil. Or, if you have a good weather station nearby many of them have soil temperature probes that could give you a good idea of what the soil temperatures are in your region.

Direct-sown lettuce germinating for a fall crop

But don’t let the cool/warm season crop designation fool you – the Cole crops like cabbage and broccoli actually have an optimal germination temperature on the warmer side, but grow better in cooler temperatures to keep them from bolting (flowering). This is why they need to be started indoors for spring planting, but you can start them outdoors (even trying direct sowing) for fall crops – they germinate in the heat and then slow growth as the temperatures drop.

Compost in Seed Starting Mix: Recipe for Success….or Failure?

A recent question posted to the Garden Professors blog Facebook group (a place where you can join and join in conversation of garden science) asked about the potential for compost added to seed starting media to cause failure in germination. It is a good question, and one that seems to have several different camps – from garden hero author folks swearing by it in their (non-peer reviewed) books, to fact sheets saying it isn’t a good idea.

I’ve always promoted that the best practice for seeds starting is using a sterile media to avoid such problems as damping off. Many of the problems I’ve heard associated with compost and seed starting are that improperly finished compost can introduce disease microorganisms to the media or cause phytotoxicity, it can make the mix too heavy and thus create anaerobic conditions that starve emerging seedlings of oxygen or cause decomposition, and there is the potential for residues of herbicides in composts using farm waste, manure, or lawn clippings as a feedstock. But does compost really pose a risk to seed starting? I decided to take a very quick spin through the literature to weigh the possibilities. Here are some of the potential issues and what a quick glance at the literature says.

Keeping the Germs out of Germination

Compost, even finished compost, has a high microbial activity. For the most part, the fungi and bacteria in compost are good guys that pose no threats to plants: they are decomposers (that only break down stuff that is already dead) or neutral. But incorrectly managed compost can also harbor fungi such as Pythium and Rhizoctonia that cause damping off or even other diseases such as early and late blight if diseased plants were added to the compost and sufficient heat levels weren’t maintained. Composts that don’t reach 140°F and maintain that temperature for several days to kill off potential pathogens run the risk of introducing diseases into seedlings.

Many promote the use of compost and compost products for potential antagonistic effects on bad bacteria. We’ve discussed compost tea and the lack of conclusive evidence that it has any effect on reducing disease here many times before, and this article found that there is no significant effect of compost tea on damping off. Some other articles, such as this one, did find that commercially prepared composts added to media did suppress damping off. However, it is to be noted that these are commercially prepared composts, which have a strict temperature requirement and often require testing for pathogen and bacterial populations. Many home composters aren’t as proficient at maintaining temperatures suitable for pathogen elimination.

Even if the compost is pathogen free, introduction into a germination media could potentially increase the population of pathogens already present in the media (or that land on it from the air) by providing a source of food for bacterial and fungal growth. The sterile mixes aren’t just sterile from a microorganism perspective, they’re also sterile from a nutrient perspective as well to help inhibit potential pathogen growth. The seeds come with their own food, so it isn’t needed for initial germination – the seedlings should be moved to a more fertile mix once they’ve established their first set of true leaves.

Image result for damping off — Damping off, source hort.uwex.edu

You may be saying- “but we also direct sow seeds outdoors, where there’s lots of pathogens present in the soil.” While this may be the case, damping off is still a definite problem in direct sowing and the loss of investment in materials, lights, and time is generally much lower (and less painful) than in indoor seedling production. This is especially the case for large operations or for home gardeners who grow lots of stuff from seed.

This is the main issue that leads to the best practice recommendation to use a sterile seed-starting mix that doesn’t contain compost. If a mix contains compost, it should be from a commercial enterprise that follows best practices or pasteurized.

Maturity isn’t just for wines, cheeses, and people

Continuing to talk about proper composting, improperly finished compost that hasn’t properly matured (finished composting) can also lead to problems with seed germination. Unfinished compost can still have woody material included, which has a high C/N ratio and also contain/release phytotoxic compounds during the decomposition process. The presence of decomposition microorganisms in a high C/N ratio means that there is still decomposition happening, which requires nitrogen for the process. With absence of nitrogen in the media, the nitrogen from the seed or the seedling can be leeched out, effectively causing mortality after or even before germination. The tender seedling serves as a source of N for the decomposing fungi.

We’ve had this discussion before when it comes mulch. While mulch is perfectly fine on top of the soil, if it gets mixed into the soil there could be potential implications on N availability.

A germination bioassay is one tool commonly used to test for compost maturity. Quickly germinating (and inexpensive) seeds are germinated on the compost (or on filter paper soaked with an extract from the compost in some commercial operations). The rate of germination vs germination failure can give some insight into the maturity of the compost. This paper discusses the use of the technique for commercial sawdust compost used for potting media.

You can use a bioassay of your own to test for compost maturity (or herbicide persistence, discussed later) for applications in your garden. Sow an equal number of inexpensive, fast-germinating seeds like radish or lettuce sown on the compost with a control sown on moist paper towel in a bag. Compare the number of germinated seeds and thriving seedlings after several days to see if there is an issue with the compost.

Keeping Things Light

One other quality required for seed starting media is a good level of porosity (pore spaces) for the media to hold air. Air (oxygen) is important as it is needed by the roots for respiration. If the media is too heavy or holds too much water you run the risk of hypoxia, or lack of oxygen, in the roots. This can result in root die off and subsequent seedling failure. Most seed starting media are composed of very light materials such as peat moss, coir, vermiculite, or perlite for this very reason. Compost, by nature, is a more dense material with less porosity and has a higher water holding capacity. Therefore incorporation of too much compost can create the potential risk of compaction or excessive water holding in the mix.

When Persistence Doesn’t Pay Off

Most herbicides break down during the composting process through a variety of physical and biological interactions. However there have been reports of some herbicides that are persistent after the composting process, resulting in a residue that could damage plants grown using the compost (see this paper for some examples). Many of the reports show the damage manifesting in mostly large applications of compost to gardens. However, the more fragile nature of germinating seeds and young seedlings make them especially susceptible to herbicide residue damage. For further discussion (and examples of bioassays used to detect herbicide residues), check out this paper.

So the potential for pathogens, risk of improperly matured compost, effect on porosity, and potential for herbicide persistence present some significant risks to germination if they are incorporated into seed starting media. These are the risks that cause many sources to promote using sterile seeds starting media, and I think the advice is well founded. While some may not experience these possible issues, the potential is still there.

The Myth, the Legend, the Parasite: Romance, Lore, and Science beneath the Mistletoe

As we hurdle ever closer to the holidays and the end of the year, there’s lots of plants we could talk about – amaryllis, poinsettias (and the abuse thereof with glitter and paint), whether or not your cactus celebrates Thanksgiving, Christmas, Easter or is agnostic, and on and on. Each of these plants have an interesting history and connection to the holidays, but today we’re going to be a little more naughty…but nice. We’re going to talk about mistletoe.

Now, mistletoe is one of those holiday plants that you don’t really want growing in your own garden. That’s because, even though it is a symbol of love and even peace, it truly is a parasite … and poisonous. It has been celebrated and even worshipped for centuries, and still has a “naughty but nice” place in holiday celebrations.

Burl Ives, as the loveable, banjo-playing, umbrella-toting and story-narrating snowman in the classic “Rudolph the Red-Nosed Reindeer” claymation cartoon tells us that one of the secrets to a “Holly Jolly Christmas” is the “mistletoe hung where you can see.” But where does this tradition of giving someone an innocent (or not-so-innocent) peck on the cheek whenever you find yourselves beneath the mistletoe come from? And just what is mistletoe anyway?

While mistletoe specialists need mistletoe, the reverse does not holdâmistletoe in many regions is dispersed solely by dietary generalists. — Distribution of mistletoe (and mistletoe specialist birds). Source: Mistletoe Seed Dispersal. Watson, D.M.

There are around 1500 species of mistletoe around the world, mainly in tropical and warmer climates, distributed on every continent except Antarctica. In North America, the majority of mistletoe grows in the warmer southern states and Mexico, but some species can be found in the northern US and Canada. A wide variety of birds feed on the berries of mistletoe and thus disperse seeds. These birds include generalists who opportunistically feed on mistletoe, and specialists who rely on the berries as a major food source.

Mistletoe Haustoria from from Julius Sachs’ 1887 Lectures on Plant Physiology. Source: The Mistletoe Pages

First, we’ll cover the not-so-romantic bits of this little plant. Mistletoe is a parasitic plant that grows in a variety of tree species by sinking root-like structures called haustoria into the branches of its host trees to obtain nutrients and nourishment. It provides nothing in return to the tree, which is why it is considered a parasite.

A heavy mistletoe infestation. Source: Pixabay

Mistletoe grows and spreads relatively slowly, so it typically does not pose an immediate risk to most trees. While a few small colonies of mistletoe may not cause problems, trees with heavy infestations of mistletoe could have reduced vigor, stunting, or susceptibility to other issues like disease, drought, and heat. So be on the lookout for mistletoe in your trees and monitor it’s progression.

This little plant does have a long and storied history — from Norse mythology, to the Druids, and then finally European Christmas celebrations. Perhaps one of the most interesting things about the plant is the name. While there are varying sources for the name, the most generally accepted (and funniest) origin is German “mist” (dung) and “tang” (branch). A rough translation, then, would be “poop on a stick,” which comes from the fact that the plants are spread from tree to tree through seeds in bird droppings.

“Baldur’s Death” by Christoffer Wilhelm Eckersberg (1817)

In Norse mythology, the goddess Frigga (or Fricka for fans of Wagner’s operas) was an overprotective mother who made every object on Earth promise not to hurt her son, Baldr. She, of course, overlooked mistletoe because it was too small and young to do any harm. Finding this out, the trickster god Loki made a spear from mistletoe and gave it to Baldr’s blind brother Hod and tricked him into throwing it at Baldr (it was apparently a pastime to bounce objects off of Baldr, since he couldn’t be hurt).

Baldr, of course, died and Frigga was devastated. The white berries of the mistletoe are said to represent her tears, and as a memorial to her son she declared that the plant should represent love and that no harm should befall anyone standing beneath its branches.

The ancient Druids also held mistletoe in high esteem, so high that it could almost be called worship. During winter solstice celebrations, the Druids would harvest mistletoe from oak trees (which is rare — oak is not a common tree to see mistletoe in) using a golden sickle. The sprigs of mistletoe, which were not allowed to touch the ground, would then be distributed for people to hang above their doorways to ward off evil spirits.

While the collecting and displaying of mistletoe was likely incorporated into celebrations when Christmas became widespread in Europe in the third century, we don’t really see mention of it used specifically as a Christmas decoration until the 17th century. Custom dictates that mistletoe be hung in the home on Christmas Eve to protect the home, where it can stay until the next Christmas Eve or be removed on Candlemas (which is Feb. 2). The custom of kissing beneath the parasitic plant isn’t seen as part of the celebration until a century later.

Washington Irving, who more or less reinvigorated the celebration of Christmas in the United States in his day and whose writings still define the idyllic American Christmas celebration, reminisced quite humorously about mistletoe and Christmas from his travels to England. He wrote:

“Here were kept up the old games … [and] the Yule log and Christmas candle were regularly burnt, and the mistletoe with its white berries hung up, to the imminent peril of all the pretty housemaids.”

Whether or not your housemaids will be in peril, the hanging of the mistletoe can be a fun Christmas tradition. Look for it at garden centers and Christmas tree lots this season. Or maybe you can find some growing wild and harvest it for your own decor. However, I would recommend not getting it out of the trees the “old Southern way” — shooting it out with a shotgun.

Sources:

Tainter, F.H. (2002). What Does Mistletoe Have To Do With Christmas? APSnet Features. Online. doi: 10.1094/APSnetFeature-2002-1202
Briggs, J. (2000). What is Mistletoe? The Mistletoe Pages – Biology. Online. http://mistletoe.org.uk/homewp/
Watson, DM. (n.d.) (accessed). Mistletoe Seed Disperal [Blog Post]. Retrieved from https://ecosystemunraveller.com/connectivity/ecology-of-parasitic-plants/mistletoe-seed-dispersal/
Norse Mythology for Smart People. (nd) The Death of Baldur. Retrieved from https://norse-mythology.org/tales/the-death-of-baldur/