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.

Image result for soil analysis reportYour 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

Give me your huddled root masses yearning to breathe free

About this time last year I posted photos of the installation of my new pollinator gardens (all perennials). As you can tell from the photos below, all of these plants have not only survived but thrived with their midsummer rootwashing.

Garden 1. Robust perennials! Except for the the sad, tiny lavender in the lower right hand corner (discussed below).
Garden 2 is just like the other, except the strawberry groundcover is replacing the wood chips.

 

 

 

 

 

The only ones that didn’t make it were the six Lavandula stoechas ‘Bandera Purple’ (see above). They did fine through the summer and well into winter. But with our surprise snowstorm in February (along with a 20-degree temperature drop in one night – from 33 to 14F), all but one of these marginally hardy plants (USDA zones 7-10) gave up the ghost. I won’t make that mistake again. But I will continue to root wash ALL of my perennials before I plant.

It’s pretty easy to excavate this tree (planted months ago) since there is NO root establishment.

And since it’s Independence Day here in the US, I thought I’d continue with the “free your roots” theme and discuss the medieval torture system that passes for recommended B&B tree installation practices. I’m talking about the burlap, the twine, and the wire baskets that are left on the root ball and cunningly hidden underground to do their damage over the years.

THIS is what should be planted.
Not this.

 

 

 

 

 

There is a great deal of disagreement about what to do with all the foreign material that’s used to keep tree root balls intact during shipment. To be clear, that is the ONLY thing they are intended to do. There is no research that shows leaving them on benefits the tree at all. The reason they are left on is because it’s more economically feasible for the installation company to do it this way. Personally I think that’s a pretty crappy reason, particularly when you are looking at trees that can cost hundreds or thousands of dollars.

Does anyone seriously think this is a good way to plant trees?

Most studies that have addressed the issue have been short term: two or three years, rarely longer. Irreversible damage to roots can take years to develop. It’s useful, therefore, to look at the landscape evidence to see what happens with all these barriers to root growth and establishment.

Death row.

Arborist and landscape designer Lyle Collins recently excavated the remains of trees that had been installed in 1991. The trees had died years ago and certainly hadn’t grown much as evidenced by their trunk size.

Not much trunk growth in this tree.

But while the trees didn’t survive, the burlap, wire basket, and webbing were all still there almost 30 years later.

Basket and webbing are clearly visible (after washing)…
…as is the burlap (before washing)

 

 

 

 

 

 

 

The clay rootballs are nearly intact as well. That’s not what you want to see. Roots must establish outside the rootball into the native soil, or they won’t survive.

Intact rootball after 28 years
The same rootball after washing

 

 

 

 

 

 

 

Eventually I’m convinced long-term research will show the folly of leaving foreign materials on the rootballs of B&B trees. In the meantime, I’ll continue to plant trees in a way that ensures their roots are in contact with the native soil and free from any unnatural barriers to growth.

 

 

 

Urban Gardening Considerations

Along with the trends of buying local food, buying organic, etc., there seems to be an increasing interest in the ultimate local food source – a garden. This includes in urban areas. Urban gardening is a great way to save money on food, a great source for fresh vegetables – especially in “food deserts”, and an easy way to introduce kids to where the food on their plate comes from. However, there are a couple potential obstacles you should consider first before starting your urban garden.

"Graze the Roof" by Sergio Ruiz
“Graze the Roof” by Sergio Ruiz

First, in urban environments the possibility that soil could have been contaminated with heavy metals, petrochemicals, etc. is pretty high, especially in older neighborhoods. Lead, which was once a common additive to gasoline and paint, is a common contaminant in urban soils.  and can be absorbed by the roots of the vegetables you grow. Because of this, that lead can eventually end up in the food on your plate. Most lead poisoning comes from ingesting lead (like eating lead paint chips…), so it’s important to know that the soil you’re using for your garden is safe. You should take some soil samples and send them to a lab in your state that can test for heavy metals like lead. Usually the Land Grant university in your state (if you’re in the US) will have a soil testing lab where these tests can be performed for a nominal cost. Other forms of contamination are possible as well, such as chemicals from cars, asphalt , laundry-mats, etc. These chemicals are more difficult to test for, so your best bet is to find out the history of your garden plot. These records should be available from your local city government, perhaps even online. Read more about contamination in this post.

Second, urban soils are often compacted from foot, car, or perhaps machinery traffic. Compacted soils make it difficult for plants to grow, mainly because the plant roots are not strong enough to penetrate the compacted soil, and thus cannot gather enough water or nutrients for the plant to survive, let alone grow and produce vegetables. Compacted soils are especially common in newer housing developments where entire blocks of houses were built around the same time. The construction companies often remove all of the topsoil prior to building the houses. The soils are then driven over by construction machinery and compacted. Then sod is laid directly on top of the subsoil. This makes for soils with very poor growing conditions for both lawns and gardens.

A good alternative for areas with either contaminated or compacted soils is to use a raised garden bed with soil that was brought in from a reliable source. You can buy bags of potting soil from a local home and garden supply store, but a more economic alternative is to have a trailer full of topsoil trucked to your raised bed. When you build your raised garden, be sure to use untreated wood. Some of the chemicals used to for pressure treated lumber are designed to kill fungi that break down wood. These chemicals, some of which contain arsenic, can leach out of the wood and into the soil used for your veggies! However, untreated wood, though it might not last as long, will still last for decades and is probably cheaper anyway. There are lots of great designs and how-to sites that show you how to build a raised garden bed. Here’s an extension bulletin from Washington State University on raised bed gardening. The raised beds shown below are from when I first installed them in my community garden plot in Manhattan, Kansas. One is now a strawberry patch (the border helps contain the strawberries to a defined area), and the other is used for mostly cold season crops.

This image shows two raised garden beds with freshly added soil and surrounded by straw in a garden plot.
Raised garden beds in Colby Moorberg’s community garden plot.

Space is also another consideration. If you don’t have the space for a garden or a raised garden, then perhaps you need to think outside the box (raised garden pun intended) and consider container gardening. Container gardening is exactly what its called – growing ornamental or vegetable plants in containers. Containers can be traditional plant pots, buckets, plastic totes, or any other container with an open top.

The advantages of container gardening include:

  • Containers can be arranged to optimally use the space available, or rearranged if you like to mix things up sometimes
  • Potting soil can be used, and can be trusted to be lead/chemical-free
  • Work can be performed on a bench, thus avoiding working on your knees
  • Containers can be arranged to provide decoration for your outdoor space
  • Many objects found around the house can be cheaply converted into decent containers
Vertical Pallet Garden. Photo by Heather Foust

Vertical gardening is a version of container gardening that uses your available space  efficiently. Much like using shelves to save space inside your home, vertical gardens use shelves, stairs, racks, etc. to make use of vertical space. The options for vertical gardens are only limited by your imagination. Here are a few extension bulletins on vertical gardening from Tennessee State University and the University of Nebraska.

The main disadvantage of container gardening is that you’ll likely have to water more frequently, but there are strategies to overcome that problem – see my prior blog post about saving water with container gardening. Another good resource is the University of Illinois Container Successful Container Gardening website.

In summary, the biggest obstacles to urban gardening are soil contamination, soil compaction, and space limitations. I’ve given you a few good alternatives to overcome those issues. Also, be sure to fertilize appropriately, lime as needed, and make sure the plants that you pick are appropriate for the sunlight that’s available. Your local garden supply store or extension agent can help you with suggestions on those issues.

If you know of an urban gardening obstacle that I didn’t address, please leave a comment and I’ll see if I can help out.

Happy digging!

Colby

This was originally posted on Colby’s soil science blog, ColbyDigsSoil.com. Some edits, updates, and adaptions were made for this post.

The Dog Days are here

The dog days of summer are here and as we approach the longest day of the year (summer solstice is June 21st), we are also feeling the advance of high summer temperatures. Long days mean more evapotranspiration and water withdrawal from the soil. During these long days, plants photosynthesize more, grow more, and use the most water during the month of June.  In fact evapotranspiration looks generally looks like a bell shaped curve when plotted by month (figure 1).  Soils dry quickly and irrigation or rainfall may not keep

Figure 1. Evapotranspiration data by month. Image from US geological Survey

up with plant demands for water. This can bring some very real stress to garden plants and turfgrasses.  If you live in a place that does not receive summer rainfall you will certainly need to increase irrigation to reflect day length at this time of year.

Transpiration is water loss through leaves and is not  part of photosynthesis, but it is critical to cool the plant. As soils dry out, the level of abscisic acid produced in roots increases and translocates to leaves resulting in the closing of the pores called stomates. Closed stomata reduces transpiration, but only at a steep cost to the plant. That cost is heat build up. Since this is also the time of the hottest weather it is not long before leaf temperatures rise to lethal levels and sunburn results. Sunburn is always seen as damage in the middle of the leaf because that is the hardest spot to dissipate the heat. The edges that lose heat rapidly are usu

Figure 2. Sunburn occurs in the middle of leaves as in this Windmill palm (Trachycarpus fortunei)

ally not burnt (Figure 2).

Short of applying water properly, what else can be done?   Mulches are a great way to avert drought stress since they reduce water loss from the soil surface. The effect is greatest where sun hits the soil. So in new gardens or gardens without a lot of shade, mulches are essential during hot weather to reduce plant stress. Wood chip mulches are particularly helpful in that wood does not reflect, hold or emit heat as much as soil, so it protects adjacent plant surfaces from heat.

How about water absorbing polymers or hydrogels? While much of the allure of these “water crystals” has worn off, it is still good to remind that polymers don’t change evapotranspiration rates of plants so even if they did all the things they claim to, they won’t get plants through a hot summer any better than if they were not present in the soil.

With the longest days come warming soil temperatures.  Hot soil can affect plants especially perennials.  Ground that is not mulched will radiate infrared onto plant surfaces, this can increase stress. This is yet another reason to employ wood chip mulches around perennials.

Figure 3. Impact sprinklers raise humidity on very hot days relieving plant stress

So when it is particularly hot and dry how can we get plants through this stressful time? Running sprinklers (where practical) will increase humidity and if soils are dry reduce stress (Figure 3).  For annual plants, some shade is often helpful. Applying shade cloth to sensitive or newly planted/emerged plants can cut stress dramatically.  As plants establish, the shade can be gradually removed.  Keep irrigation even so moisture is always there to maintain transpiration — this  is essential during warm weather and long days. For perennial plants there is not much to be done. While pruning will reduce the amount of surfaces that lose water, pruning (thinning) will also lead to temperature increases in the plant canopy since the evaporative surface area of the plant is decreased. So while soil water is saved, canopy temperatures may rise, this may be a poor trade off in the hottest months of the year.  Over-pruning opens plants up for sunburn on stems which can lead to fungal canker infections by pathogens like Botryosphaeria. This is very common in Apples.

Another treatment you may have heard claims for are anti-transpirants. These are products that are sprayed on plants to create a film that will cut water loss from leaves. Taken from a recent Amazon search I found the following product description recently… “Product is a water-based, semi-permeable polymer coating that can minimize the damages from climate related stresses, such as frost and freeze, heat stress and sunburn, drying winds, and transplant shock. Applied as a foliar spray, Product provides a unique non-toxic, biodegradable, elastic membrane over the plant surface to reduce moisture loss and insulate the plant.” While there may be an application (such as freeze protection) that makes sense for this kind of product somewhere, I don’t see it in your garden during hot weather. Cutting transpiration (“reducing moisture loss”) will increase the heat on leaves, so one of the common side effects of using these products is hot weather is damage or phytotoxicity.  Like polymers the fad is faded.

Sometimes the dog days of summer bring insurmountable challenges. In early summer of 2018 in California, temperatures reached record levels of 115-120. Even in irrigated situations plants were damaged, short of providing immediate shade, there was nothing to be done and many plants were injured, even native plants are not adapted to such high temperatures. If these conditions occur in your garden, you may not be able to limit damage, but there are considerations for after care when this kind of blitz occurs. Don’t prune anything immediately, let the leaves fall and buds form because stems may be intact. Prune away injured plant parts after regrowth begins. If injury is severe, cut back on irrigation. Injured plants don’t require as much water because there is less functional  leaf area. This is why root root rot often follows this sort of severe injury. The summer solstice is here—I can already feel the shortening days of fall some distance away.

Reference

Costello, L.R., E.J. Perry, N. P. Matheny, M.J. Henry, and P.M. Geisel.  2014.  Abiotic disorders of Landscape Plants.  University of California Division of Agriculture and Natural Resources Publication #3420.

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.

How green were my peppers…

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.

Image result for ethylene

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
Papaya
Pawpaw
Peach
Pear
Plantain
Plum
Tomato
Cherry
*Some evidence of climacteric ripening in hot peppers

Image result for avocado ripe meme

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
Getting close…

 

 

 

 

 

 

 

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.

Grapes must stay on the vine to ripen

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 botany53(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 Science175(1-2), 114-120.

Lelièvre, J. M., Latchè, A., Jones, B., Bouzayen, M., & Pech, J. C. (1997). Ethylene and fruit ripening. Physiologia plantarum101(4), 727-739.

Cornmeal magic – the myth that will not die

Way back in 2010 (and then again in 2012) I wrote about a bizarre belief that cornmeal could be used to treat fungal diseases, from lawn spot to athlete’s foot. Rather than rehash what’s already been written, I’ll invite readers to read those posts for background. And of course look at the comments, which are…interesting.The weird thing is that this post from 2010 is the single most popular post on the blog. (Our stats are only for the last two years since we migrated the web site – who knows how many there were before May 2017?)

Blog stats over two years

The consistent popularity for the topic spurred me to publish a university fact sheet on the use of cornmeal and corn gluten meal in home landscapes and gardens. This fact sheet reviews the pertinent literature, and makes recommendations that are pretty much the same as those I made almost 10 years ago. Nothing has changed in the research world to support cornmeal as a fungicide.

But wait, there IS something that’s happened since 2010! Now cornmeal is being touted as an insecticide! In fact, if you go to Google and search for “cornmeal” and “insecticide” you’ll find thousands of hits.  As you might expect, there’s no research to support this notion: researchers in Maine, for instance, found no effect of cornmeal on fire ants. However, it is used as a bait to deliver actual insecticidal chemicals.

Way back in 1937.

But facts don’t get in the way of home remedies, such as Lifehacker’s eyebrow-raising advice.

Hmmm…

By refining the search to only include university websites (use “site:.edu” to do this), and swapping out “ants” for “insecticide,” you’ll find at least one Master Gardener group happily (and illegally) recommending cornmeal as an ant killer. The popular mode of action is either (1) they can’t digest cornmeal and starve or (2) the cornmeal absorbs water in their gut and they explode.

Boom!

This reminds me of yet another food product – molasses – recommended for killing ants. Since you’re already here, you might as well check out Molasses Malarkey parts 1, 2, and 3 too.

Might I recommend everyone use their cornmeal and molasses to make bread or cookies or pancakes? There are some delicious recipes on the internet.

Yum!

Bare Rooting – a guest post from a commercial landscaper

What are these trees and do they look like this? Read on to find out!

Today’s blog post is courtesy of Mary Blockberger of Sechelt, BC. As you’ll see, Mary and I go way back.  I thought it was important to our ongoing discussion to see how the industry can use the root-washing technique effectively and economically. Here’s Mary:

“Before I began managing the Sunshine Coast Botanical Garden in Sechelt, BC I had a small residential landscaping company.  By small, I mean that I was the employee of the month every month of the year!  One of our Garden’s mandates is to provide relevant and educational programs for our community.  Dr. Linda Chalker-Scott has been one of our most popular speakers several times.  One of her presentations dealt with the practise of bare-rooting perennials, shrubs, and trees prior to planting, and the tremendous advantages of following this method.

Root-washing and installing 36 Carpinus. November 2007.

“In November, 2007 I had a chance to try this technique out.  My client wanted a ribbon of Carpinus betulus ‘Fastigiata’ planted that would eventually be pleached into an interesting pattern.  [Pleaching is a formal tree training technique.] There was a total of 36 trees to be planted; most were container stock as I recall but there may have included a couple of B&Bs as well.  Working with another local landscaper, into a wheelbarrow of water went every single tree one at a time.  The dirt was clawed away from the root balls by hand with a final spray from the hose.  Honestly, it was a cold and miserable job, and I believe a few curses directed at Linda ensued.  However, once the roots were cleaned of all soil planting was a breeze.  It’s a lot easier moving trees without moving the soil too.

Carpinus are well established and pleaching is underway. April 2009

“Flash forward 12 years, and every single tree has flourished.  Bare rooting allowed us to identify and correct any problems before planting, and I’m sure this has a lot to do with the trees’ success.  It’s a time consuming and at times messy method, but the reward of a healthy row of trees is well worth the effort, IMHO.”

Pleached Carpinus hedge May 2019

And let me add to Mary’s account that a ZERO replacement rate is going to pencil out to long term economic success. I was able to see these trees earlier this year – that’s my photo at the top of this post.

Amending Soils—Why??

I think the blog and garden professors web page is pretty full of research and benefit descriptions of mulching, particularly with arborist chips. A little less clear is the role of amendments in garden soils. I always like to ask the “why” questions for gardening practices. Like “why” prune trees? Why fertilize, etc? Ideally gardening practices should be founded on a basis of science and inquiry as to their necessity. Poor structure early structural training or a damaged canopy may prompt tree pruning, mineral nutrient deficiency symptoms may suggest

When amending, organic materials are often tilled in 50% by volume (3 inch layer tilled six inches deep)

fertilization. So why amend your garden soil? For me as a gardener you do this because your soil is not providing something you think your garden or plants growing in that soil need. This could be nutrients, or water. Amending as a soil or garden practice is best done in garden beds that host annual plants: vegetable gardens, color beds with annual plants etc. Obviously we are not going to lift all the perennials just to add some amendment under their root systems. We can also make arguments that amending soils that you are going to plant perennials in is unlikely to be helpful. So why amend?

 

Research on providing amendments in the holes of perennial plants has most often shown no significant differences compared to plants installed with just native backfill. There are lots of reasons for this and I can imagine some soils where amendments would give a slight boost, but these were not the soils most studies used (extreme sands). Mostly, perennial roots do not reside in the planting hole for long, so the time that amendments would be effective is very short. Since amending can also harm some plants if done incorrectly, University of California does not recommend the practice, neither did Harris for trees, shrubs and vines. Nor did we find any effect in palms (Hodel and others). For this blog we will assume that amending is restricted to annual plant beds. So why amend? The usual reason I hear is: “My soil is crap!” I think it would be interesting to survey people about their soil and see what they think about it as compared to how it actually grows. Most people seem to disparage their poor soil….So many gardeners believe that if they add something to their crap soil it will get better. Maybe, or no. Amending has potential benefits and detriments depending on what and how much you amend with.

snaps growing in soil amended with high quality yardwaste compost
Snaps growing in soil with uncomposted yardwaste used as an amendment. Nitrogen is immobilized

So the potential benefits of amending are:
• rapid (immediate) modification of the planting bed
• potential increase of moisture holding capacity in the soil
• potential increase of nutrients and nutrient holding capacity (cation exchange capacity of the soil
• change in the soil texture, porosity
• rapid increase in soil organic matter
• suppression of soil borne pathogens

Potential detriments include:
• nutrient draw from the soil (nitrogen immobilization: see images above)
• toxicity from residual phytochemicals
• adding pests (weeds or root pathogens)
• soil structure is destroyed
• soil food web is challenged and harmed
• may increase soil salinity
• contaminants can be transferred to gardens

One of the incontrovertible facts about amending is that you have to disturb the soil to do it. Amending involves digging in, roto-tilling, soil turning with a spade, or some kind of incorporation process. Usually the more the better. This destroys soil structure and a good part of the soil food web. Beneficial nematodes are highly sensitive to tillage and many are killed by tillage, often perturbing the entire soil food web in a disturbed soil (See research by Howard Ferris). The beauty of mulching is that the soil structure is not initially influenced only assisted in its further development. The downside is that mulches take months or years to have their effect. While amending can give immediate physical, chemical and biological assistance to soil, it also may bring pathogens, salts, toxic phytochemicals or weeds to your garden depending on what you choose to use as an amendment. Soil tends to be very resilient, so structure destroyed by amending is usually back in place at the end of the cropping cycle in many cases. The need for further amending should be considered carefully after each rotation.

So you still want to amend? What do you amend with? In the case of mulching we (Garden Professors) make a strong argument for freshly prepared (not composted) arborist chips. Nothing could be worse for amending (at least in the short term). Un-decomposed substrates such as wood chips are high in carbon and low in nitrogen. They will cause the microbial community of soil to attack the carbon and utilize all the free nitrogen in the soil, screened or fine materials after composting have greater surface area and will enhance the water absorbing and nutrient holding properties they give to soil. Furthermore, well composted substrates or feedstocks will be free of pathogens and other pests so they should be “safe” for your garden. Composts that are made from plant feedstocks tend have concentrations of plant required minerals. Since composts lose about 2/3 of their carbon and moisture during the decomposition process they have a much higher mineral content than their feedstock. Manures have already been partially composted by the animals that made them. Additional composting increases their salt levels sometimes to plant damaging levels. Manures should be used with care, or in lower quantities as they can damage sensitive plants. Some manures and composts can be contaminated, since some long term soil-residual herbicides such as clopyralid are not broken down in the composting or animal eating process.

soil amended with peat moss
Soil amended with composted coffee grounds

Gardeners are inventive in their use of compost and amendments, so there are many ways to amend soil. Peat moss has been the gold standard amendment for many gardens. However due to environmental damage, sustainability of peat moss use is questionable. Coco fiber or coir is a good amendment, but it can bring high salts with it depending on how it was processed. Biosolids are phenomenal amendments and often produce growth responses, but there can be issues with metals and other biological contaminants in biosolids. Home-made compost is a good amendment because you know what is in your compost, as long as it is properly prepared and cured, it can function very well. Greenwaste or yardwaste compost is a possibility, but from my experience, most of these if commercially produced are not well prepared, and are not mature (they still heat up if piled). Many gardeners like coffee grounds, and with the advent of large coffee companies, grounds may be available in bulk quantities. Be careful though as some sources of coffee are toxic to many plants and their use should be limited in any amending situation.

What about rate? In my research I have always tried to amend soils 50% by volume. So a three inch layer of amendment tilled six inches deep has been my goal. Most annual plants have their roots in the upper six inches and this strategy works well. Also, most rototillers are only good for about a six inch depth. If you intend to dig deep with a spade and incorporate to depths beyond six inches, increase the amounts accordingly.

What kind of soil needs amending? Another way to view this is, “have you tried growing without amending? Many soils grow very well with just added nutrients. Typically sands will most benefit from added amendment due to increased water and nutrient holding capacity. I also like to amend clays because they become easier to plant in over time, however the initial go round may be difficult. Clays are very nutritive so amendments may make you feel better gardening in them, but often plants grow very well without amending clay soils. Plant responses to amendments are best in sands.

How often should I amend? This is up to you, but organic matter is “burned up” by the soil microbial community rapidly because 1) you are tilling and this accelerates microbial activity; and 2) you are likely amending during the growing season when warm soil temperatures favor organic matter breakdown. Most gardeners amend prior to replanting the bed.

References

Ferris, H., and M.M. Matute. 2003. Structural and functional succession in the nematode fauna of a soil food web. Applied Soil Ecology 23:93-110

Harris, R.W. Arboriculture: Integrated management of landscape trees, shrubs and vines. 1992. Ed. 2 Prentice-Hall International, New Jersey. 674pp.

Hodel, D.R., Downer, A.J., Pittenger, D.R. and P.J. Beaudoin. 2006. The effect of amended backfill soils when planting five species of palms. HortTechnology 16:457-460.

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.

Planting with a “flare”

Anyone who plants or cares for woody plants eventually hears the term “root flare” (or root crown). It’s easy to describe a root flare (it’s the region where stem or trunk morphs into roots). What’s sometimes difficult or even impossible is finding it in improperly planted trees and shrubs.

Conifer root flare
Angiosperm root flare

 

 

 

 

One of the primary causes of tree and shrub failure is improper planting depth. This is not a problem with bare-root plants, as you can easily see the region of transition. During planting you should make sure that the root flare is at grade, so that the roots are underground and the stem/trunk is above ground. The only mistake you can make with bare-root plants is to plant them upside down.

Grafted bare root trees clearly show root flare

The problem really started with the advent of containerized and balled-in-burlap (B&B) plants. This technology is less than 100 years old, and before it existed everything was either planted from seed or from bare-root stock. It’s possible to use containers and B&B properly for temporarily housing trees and shrubs, but increasingly automated production methods with unskilled workers and undereducated supervisors means increasing numbers of poorly planted woody plants entering the retail market.

Vine maple planted too deeply in container
Tree buried too deeply in burlap

 

 

 

 

 

 

I’ve written earlier posts about how to select plants at the nursery. As you’ll note, finding the root flare can often be impossible without removing container media or B&B burlap. Because so many people are unaware of the problem or unwilling to disturb the root ball, these plants are then installed with the root flare still buried.

Lilac planted too deeply
Pine tree planted too deeply

 

 

 

 

 

 

Why does it matter if part of the trunk is underground? For some species, it really doesn’t matter. Wetland species, for instance, can tolerate low soil oxygen levels and submerged trunks. But most of us are not planting wetland species, and many ornamentals are not tolerant of this treatment. Roots that are buried too deeply don’t receive enough oxygen to survive, and the plants respond by trying to create a new root system. These adventitious roots are unable to supply enough water to the growing crown, however, meaning shrubs and trees suffer chronic drought stress when the rate of evaporation exceeds the ability of these substandard root systems to supply water.

With only skimpy adventitious root system to take up water…
…this tree suffers chronic drought stress every summer

 

 

 

 

 

 

There are other problems, too. Stem and trunk tissues of non-wetland species are not adapted to being buried. The excessive moisture and lack of oxygen contribute to the attack of opportunistic pests and diseases, both of which can cause irreversible damage and eventual death. You can even see this happening to plants in the nursery.

Rotted trunk clearly visible in improperly bagged B&B

Finally, consider this landscape evidence of the impact of buried root flares. These magnolias are all planted on the campus at Princeton University. The one of the left is significantly smaller than the other three. A close up of the trunks explains why.

One of these trees is not like the others
Magnolia tree under stress from being buried too deeply
This magnolia tree thrives with its root flare clearly visible

 

 

 

 

 

 

 

 

If you have newly planted trees that look more like telephone poles than trees, the best thing you can do is dig them up and plant them correctly.