You can have your trees and save water, too!

Cake is good, but so are trees.
Photo courtesy of Flickr user Son of Groucho.

Today’s blog post title is a play on the old saying “you can’t have your cake and eat it too.” In other words, once you’ve eaten the cake, you don’t have it anymore. Likewise, if you have a tree, you’ll need to use a lot of water which might run afoul of water restrictions. Or will it? Today’s post demonstrates that you can have healthy trees AND save water at the same time.

May 2019. The camphor (and the lawn) is relatively healthy before three years of drought. Photo courtesy of Google Maps

A few weeks ago I got an email from ISA-certified arborist and blog reader Curtis Short, who wanted to share his success with rejuvenating a prized landscape tree that had become severely stressed as a result of residential water restrictions. The tree is camphor (Cinnamomum camphora), which grows well in warmer parts of the country (USDA hardiness zones 9b-11b). This particular tree is about 40 years old and the showpiece of a residential landscape in the Oakmont neighborhood of Santa Rosa, CA.

March 2022. Nearly all the leaves on the camphor have become chlorotic after three droughty years and lack of irrigation since the previous spring. Photo by Curtis Short.

In March 2022 Curtis received an email from the homeowner (a retired meteorologist) who was concerned about the declining health of the camphor after irrigation was discontinued in mid-2021. Prior to this, the sprinklers were run daily during the dry months to support the tree as well as the surrounding lawn. The lawn, with its shallow but dense root system, recovers quickly with seasonal rains. The damage to the tree’s root system, however, has led to leaf senescence and drop.

Two other arborists had given the tree a thumbs down: one said it needed to be removed and the other said that even if the tree recovered it would never regain its original form. Curtis chose a different approach, suggesting that the homeowner could resuscitate the tree by:
*removing competition (the lawn) for water and nutrients,
*refining the irrigation system,
*applying nitrogen to stimulate new leaf growth, and
*supplying an arborist chip mulch to the landscape.

May 2022. Tree resuscitation efforts began in March, as chlorotic leaves continue to drop. Photo by Curtis Short.

In April the homeowner applied glyphosate to kill the lawn, removed the old lawn sprinkler system, and replaced it with a 100-foot drip irrigation system near the canopy dripline and outwards where most of the tree’s fine roots are located. (For those who are curious, the system consisted of 12-inch spaced Techline emitters with a 0.9 gallon per hour dispersal rate.) Next, a layer of arborist wood chips were applied to at least a 4” depth. In May, ten pounds of ammonium sulfate (a great source of nitrogen) were applied on top of the chips and watered in.

June 2022. Tree recovery begins along with a new irrigation regime. Photo by Curtis Short.

The homeowner’s irrigation plan departed dramatically from the original daily watering routine. Being a retired meteorologist, the homeowner was naturally interested in collecting data. The original two lawn stations each put out 45 gallons per day, for a total lawn water usage of 630 gallons per week. With the new drip irrigation system, irrigation was limited to one 35 minute application per week, with a total weekly water use of 105 gallons.

July 2022. The tree canopy has markely improved in color and density with new leaf growth. Photo by Curtis Short.

Curtis photographed the tree’s recovery as a way to reassure the homeowners that the tree was neither dead nor disfigured. The homeowners are now aware that trees cannot go “cold turkey” in efforts to reduce irrigation water use. Locating the drip system beneath the mulch layer means evaporation is reduced and that the mulch layer stays hydrated, supporting its population of mycorrhizae and other beneficial microbes.

September 2022. In August, a second application of 10 pounds of ammonium sulfate was applied and watered in. Photo by Curtis Short.

I appreciated Curtis sending me this case study as we all face the likelihood of hotter temperatures and possible water restrictions. Reduction of water-hungry ground covers, judicious use of water, and a living layer of arborist wood chips are key to helping our landscapes survive.

May 2023. A little more than a year after resuscitation efforts began, the dark green tree canopy is full and healthy. Bare branches have all but disappeared, and the tree’s health is arguably better than it was in 2019 before the three-year drought period. Photo by Curtis Short.

Crop rotation makes the garden go ’round

You might have heard of the concept of crop rotation, or even have had someone tell you that you should be practicing it in your home garden. But does this practice developed for use on large-scale farm fields work for small-scale home gardening or backyard farming?  And if so how do you even do it? Let’s take a quick look at the practice and learn how you might implement it in your own garden, no matter the size, if it is practical to do so. 

The Benefits of Crop Rotation

The benefits of crop rotation touted to home gardens for annual fruit and vegetable plants focus mainly on Integrated Pest Management. Keeping certain crops in one spot in the garden year after year can lead to a build up of plant disease microorganisms and insect pests in that area. These findings are largely based on large-scale production systems, like where whole fields that are hundreds of acres are grown as the same crop and switched from year to year. But there still is some benefit for the small-scale gardener, especially with disease build up from soil-borne diseases or debris left in the garden.

The benefits are less clear for insect pests.  Sure, there might be fewer insects that move from spot-to-spot or bed-to-bed in your home garden, but we must remember that insects can fly and a journey of a few feet from one raised bed to the next might not be much of a barrier.  It is sort of like when people ask us if using grub control in the lawn will control Japanese Beetles in their garden. There will likely be a small reduction in the population, but we remind folks that Japanese Beetles can fly pretty good distances, so control will be minimal. 

Crops in rows and beds can be easy to rotate.

Benefits of crop rotation lay below the soil. Different plants use different ratios of nutrients and some even add nutrients to the soil. Legumes have nitrifying rhizobia bacteria that colonize their roots in a symbiotic relationship and there is a net nitrogen increase in the soil after legumes such as beans, peas, alfalfa, or clover have been grown. That’s why one of the major crops added to crop rotations in the “corn belt” is soybeans (or just “beans” if you’re from around these parts). The soybeans contribute nitrogen to the soil, which helps in the production system because corn is a heavy nitrogen feeder. This is especially true if the roots are left behind or if the legume is incorporated like a cover crop.

Given that crops uptake nutrients in different ratios and that some input nutrients into the soil, by planting the same crop year-after-year in the same spot you can end up with nutrient imbalances, especially in raised beds or small plot areas. Using cover crops and incorporating them into the soil is another facet of crop rotation that can build soil organic matter and address nutrient issues. Fertility can also be adjusted with fertilizer and compost, but using rotation will help with overall management.

Rotating in root crops like carrots, radishes, and turnips can also allow for some good soil aeration, especially in no or low till garden situations. 

There’s also research that shows that different plants exude different compounds, like sugars, etc. that attract and feed different microorganisms and rotations which help increase the diversity of the microbiome in the soil. This will not only improve the soil ecology in your garden, but a healthy microbiome can compete with some disease-causing microorganisms to reduce the likelihood of soil-borne disease. Most of us have been told that eating cultured yogurt increases good microbes in the gut and can reduce the likelihood of some illnesses- its kind of like that, but for plants.

How to rotate crops (especially in small gardens)

While crop rotation might not solve all the world’s problems or your garden insect issues, there are still definite benefits to the practice if you can manage it.  For some people garden space is too limited. How do you rotate crops when all you grow is a few tomatoes in the corner of a flower bed?  Other than putting them somewhere else every year, there isn’t much you can do. 

If you have a large garden and especially if you have one that’s a larger tilled-up spot (don’t get me started on tillage), you should definitely be implementing rotation. While I typically garden in raised beds, that usually makes it easy. Crop rotation usually occurs by plant family, so plant families rotate to a new bed each year (more on plant families in a bit). 

In general, a crop rotation plan should mean that plants from the same family aren’t grown in the same place in the garden for at least four years if possible.  If I plant tomatoes in “Bed A” in my garden this year, then I shouldn’t plant them in “Bed A” again for at least four years if possible.  If you’re not growing in beds, then should rotate by rows or by areas of the garden.

Is this practical for every gardener?  No. So I say do what you can. If you have a small space and only grow a few things and want to rotate crops, you can do so by time rotation – growing different crops each year.  Or adding some container gardening to the mix and rotating crops into containers in different years. As a side note, using containers can be an effective way to rotate crops because you don’t necessarily need to rotate the plants if you can rotate (replace) the soil from year to year (or at least replace the top layers). 

Crop rotation can also aid in succession planting.  For example, I don’t follow my beans with corn, I follow them with garlic, which is also a heavy nitrogen feeder and works right into the garden schedule to be planted in October after the beans are done. I’ll often do lettuce or leafy greens in a bed in early spring, then thin them out to plant in tomatoes or peppers when the time comes. Incorporating intercropping where you plant different sized plants around each other, like my lettuce and tomatoes, can also be an effective addition to crop rotation.

For a good crop rotation, you’ll want to plan.  This would involve sketching/mapping out your garden or at least labeling different beds or spaces. Then creating a chart for each space where you list what crops will be grown there for the next several years will help you plan out to make sure you are giving ample time for the rotation process.

Keeping it in the family

Family members share lots of things and plant families are no different. Not only do some crops look similar but they can often share the same diseases. Keeping families in mind planning crop rotations is one of the easiest methods to keep track of which crops to include in a rotation.  For small gardens it might make sense to keep members of the family together. For example if I only have four beds, I would want all the family members together so that I can have a true four year rotation. In larger gardens, realizing that crops are in the same family will help plan out for rotation of multiple crops. 

Also keep in mind that some crops will overwinter (depending on where you are) so a fall crop might also be a spring crop in the same bed the following year.  Some crops are also biennial depending on your local climate.  For example unless you live in an area with winters cold enough to kill them, swiss chard, onions, and other crops will survive the winter and grow the following spring. I typically leave most perennial vegetables like asparagus and rhubarb, as well as perennial herbs like oregano and chives, out of rotations and put them in their own specific place in the garden (or elsewhere) since they don’t need to be replanted every year.

I’ve put together a list of common annual crops by family, as well as an example crop rotation plan for single garden bed/area. As an example, if I had four raised beds I would use this plan for each bed, starting in a different year for each bed so that I grow all the same crops each year, just in different beds.

Common crops by family. Developed from UF/IFAS Extension
A crop rotation plan I might use in my own garden. If I had four beds, Year 2 crops would be Year 1 crops for bed B and so on.

In conclusion…

Crop rotation isn’t an end-all, be-all garden practice.  If you can institute some sort of rotation in your garden you’ll likely see long-term rewards.  However, if it isn’t possible or seems like too much work just remember don’t plant things in the same place year after year if you can help it.  Any rotation, even if it is hit or miss, will be beneficial. 

Sources

Benincasa, P., Tosti, G., Guiducci, M., Farneselli, M., & Tei, F. (2017). Crop rotation as a system approach for soil fertility management in vegetablesAdvances in research on fertilization management of vegetable crops, 115-148.

Sasse, J., Martinoia, E., & Northen, T. (2018). Feed your friends: do plant exudates shape the root microbiome?Trends in plant science23(1), 25-41.

Wright, P. J., Falloon, R. E., & Hedderley, D. (2017). A long-term vegetable crop rotation study to determine effects on soil microbial communities and soilborne diseases of potato and onionNew Zealand Journal of Crop and Horticultural Science45(1), 29-54.

Yasalonis, A. (2019) A must do in gardening: Vegetable crop rotation (UF/IFAS Extension). UF/IFAS Extension (blog)

The Yin Yang of Compost

I am constantly slaying horticultural snake oil dragons. There is so much misinformation on the web and even within University/Extension publications. In this blog I turn my attention to compost–a subject that is almost universally cherished by gardeners, gardening groups and horticulturists. Unfortunately there are a lot of misnomers about compost.

Compost is dark, earthy, smells good when aerobic is almost finished when it will no longer heat up on turning.

Plants are composed of cellulose and cellulose is a complicated polymer of glucose molecules. Compost is made from the decomposition of organic matter—usually plant debris. The composting process can be fast or slow depending on aeration, mixing and pile size. Composting requires a carbon source and enough nitrogen to allow microbial respiration of the sugars contained in the plant material being decomposed. Since the laws of thermodynamics indicate that no chemical reaction is 100% efficient, some of the energy of respiration is lost as heat. Billions of respiring microbes heat the pile creating a very hot environment where thermophilic organisms propagate quickly. As all the available sugars in leaves and other less woody components of the compost decompose the thermophilic organisms lose temperature and the readily available sugars necessary for growth. Other organisms begin to grow and attack the cellulose in the wood fibers, attacking the more recalcitrant carbon in the pile. Eventually most of the sugar bound in plant residues is attacked and only the difficult to decompose materials are left, these contain lignin and form the basis for humus. When the compost will no longer heat after turning it is beginning to mature. Once all the easily broken down carbon is utilized, the microbes die off or form spores and go into a resting phase. The compost is now screened to remove large undecomposed particles and is ready for use in the garden

It’s NOT NATURAL

I have often heard composting touted as a natural process. It is not.
Composting is a process that is “man made”. The alternative is litter fall and mulching which is a natural process that processes organic matter much more slowly. Composting is a process that requires a specific mass of feedstock, sufficient oxygen for respiration, reactions provided by air or by frequently turning the pile, moisture maintained by adding water if needed, and heat which is maintained within the pile itself. These are not natural conditions easily found in nature. They are carefully manipulated by those monitoring the compost process.


The fungi and bacteria on the initial feedstock are part of the ecosystem and are generally not directly manipulated in the process. Fungi and bacteria have the enzyme systems necessary to break the bonds that link the glucose molecules and then utilize the energy in glucose for their own growth.

Composting does not help the environment

As I have discussed, composting liberates carbon dioxide increasing the amount of greenhouse gasses in the atmosphere. On a large scale composting adds many tons of CO2 to the atmosphere as well as oxides of nitrogen which are also potent greenhouse gases. Composting can also release mineral salts into underlying soil and runoff from large composting operations, especially manure composting, can pollute waterways. There is nothing about composting that is helping the environment per se.

Sheet mulching with cardboard cuts gas exchange below. Covering with fine textured compost as is often done will exacerbate gas exchange issues.

Compost is not full of life

Sometimes you hear that compost is “full of life”. Sort of true but not really. The biological processes that break down the compost happen in the pile. As compost matures microbes die, their growth is reduced and they form spores or other resting structures. Once compost is ready for use, it is not particularly biologically active because all the energy has been utilized to make heat and decompose the feedstock. When the energy (carbon, sugar, cellulose) is used up, the microbial activity declines.

What is it good for?

Since compost is a distillation of feedstock minerals it makes an excellent fertilizer. Since compost is mostly fine textured, it is suitable for use in soil as an amendment. The lignin molecules resident in compost help bind nutrients in organic matter and retain them for later uptake by plant roots. Compost can increase the fertility of a sandy soil which has low nutrient binding capacity. Compost is full of secondary metabolites left over from the microbial activity produced when the pile was hot. These compounds can confer disease protection when pathogens are present in soil. Since feedstocks are variable this can not be predicted. Finished composts with a carbon:nitrogen ratio (C:N) of less than 25:1 do not perturb the nitrogen dynamics of most soils and in many cases may be a source of nitrogen in the amended soil. Since compost is mostly broken down feedstock it does not deteriorate as fast when mixed in garden soil. It resides longer than other more labile amendments. Compost is also a great container medium if mixed with coarse materials to assure aeration. Because the compost feedstock is well decomposed, the material has a longer life as a growing medium.

Since composts get hot as the feedstock is broken down, they tend to sanitize the pile of pathogens. Composting kills food-borne pathogens and plant pathogens easily since most do not survive the high temperatures (>140F) found in an active compost pile for more than a day or so. For effective pathogen kill it is important to turn the pile frequently.
Some plants may survive high composting temperatures, e.g, tomatoes are a notorious compost weed. Yellow nutsedge and bermudagrass stolons can also resist the high temperatures found in compost piles.

Compost can be used in container media if enough aeration is provided by other media components

It’s not a good mulch

One of the amazing things about mulch is undergoes the same processes that make compost and it does have a place in your garden. The microbial processes that decay arborist wood chips on the soil surface happen slowly over months of time. The chips are mineralized but more of the carbon enters the soil rather than the atmosphere because soil fungi, especially mycorrhizal fungi, transform the energetic carbon molecules (labile carbon) into a soil stabile polysaccharide called glomalin. This in turn binds soil particles which increases soil structure. Note: When these processes happen in a compost pile they can not happen again in your garden. The energy is gone.
Texturally fine compost will make greater hydraulic conductivity with the underlying soil and allow for greater moisture loss through evaporation. In some cases compost layers may impede infiltration of water and prevent newly planted root balls from being watered. Compost layers may also impede gas exchange to underlying soils. Depending on the feedstocks, composts may also contain viable weed seeds or other propagules that contaminate landscape soils. Composts make bad mulches.

References

Daugovish, O.,Downer, J., Faber, B. and M. McGiffin. 2006. Weed survival in yardwaste mulch. Weed Technology 21: 59-65.

Downer, A.J.,D. Crohn, B. Faber, O. Daugovish, J.O. Becker, J.A. Menge, and M. J. Mochizuki. 2008. Survival of plant pathogens in static piles of ground green waste. Phytopathology 98: 574-554.

Chalker-Scott, L. and A. J. Downer. 2022. Garden Myth-Busting for Extension Educators:The Science Behind the Use of Arborist Wood Chips as Landscape Mulches. Journal of the NACAA 15(2). https://www.nacaa.com/file.ashx?id=6c7d4542-7481-4f0a-9508-d8263a437348

Seasonal forecasting: Looking into the crystal ball

This time of year, I often get asked for a forecast for the coming growing season. Will we have a drought? Will it be warmer or colder than normal? Will we have any tropical storms in our area? All of these things affect how farm crops (and gardens) will perform over the next few months and how big the yield might be when it comes time to harvest. In this week’s blog, I will look at some of the factors that go into seasonal forecasting and how it all comes down to numbers.

Gaze Into My Crystal Ball, John Brighenti, Commons Wikimedia

How are seasonal forecasts made?

Seasonal forecasts use computer models to look for large-scale patterns in weather that affect what the climate is likely to be on monthly to seasonal time scales, but also use statistical methods based on observations from previous years to determine what the most likely climate conditions are. The predictions are usually based on several factors, including current conditions, long-term trends, and other regional variations like El Niño Southern Oscillation (ENSO), which we’ve discussed before.

Current conditions are important because they define the starting point of the prediction. If you are starting from a drought, for example, you would not expect that next month would be much wetter than normal because the dry conditions would make it hard for rain clouds to form unless you have an unusual event like a tropical storm or atmospheric river that comes along and changes conditions on the ground quickly. Long-term trends are important because they define the base state of how the climate is behaving. If you are on an upward trend towards warmer temperatures, as we are now with global warming, it is more likely that you will observe a month or season that is above normal than below normal. If there were no trend in temperature, then seasons that were colder or warmer than average would be equally likely. You can find climate trends for your local area using the Climate at a Glance tool and picking your own country, state or county.

Chart, bar chart, histogram

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Source: National Centers for Environmental Information

Knowledge about regional variations like ENSO also contributes to seasonal forecasts because the atmospheric and oceanic climate conditions which help define those oscillations can last for months or sometimes even years, making long-term prediction easier. The pattern of the atmospheric waves associated with those oscillations defines where warm and cold air are located as well as the position of the jet streams that blow storm systems around. In some respects it is like putting a rock into a river—when you have warm water in the Eastern Pacific Ocean as we do now in advance of the coming El Niño, thunderstorms develop vertically over that warm water, and those towers of rising air divert the flow of air currents that push weather systems around just as a rock diverts the flow of water in a stream. If the warm water were not there, the atmosphere would likely have a very different pattern.

Oirase Mountain Stream – Towada, Aomori, Japan, Daderot, Commons Wikimedia

Forecasts based on ENSO work best when it is at one extreme or the other and in areas where the differences between El Niño and La Niña conditions are most pronounced. That makes ENSO more useful for making seasonal forecasts in the Southeast United States and in northern states where statistical relationships are well-defined than in the central U.S., where there is a weaker statistical relationship between the ENSO phase and the local climate. Climatologists look at similarities between different El Niño years using statistics to identify recurring patterns that can help to predict the climate the next time an El Niño occurs, although other factors can come into play that throw off the forecasts.

How do seasonal forecast maps depict the future climate?

For the United States, seasonal forecasts are presented as maps with probabilities of above, near, or below normal temperature or precipitation. If there was no hint in any of the predictors of what would happen, each of the three categories would have equal weight, or a 33% chance of that climate category occurring. Those forecasts are based on current conditions, what they expect to happen in the months after the prediction made, the long-term trends that are pushing the temperatures or precipitation upward or downward, and the expected state of oscillations like ENSO. You can see the whole suite of 3-month forecasts for the next year for the United States at https://www.cpc.ncep.noaa.gov/products/predictions/90day/.

Source: NOAA’s Climate Prediction Center

In the maps above, the outlook for December 2023 through February 2024 is shown. In the temperature map, the climate has a higher probability of being warmer than normal in the northern part of the country, especially the Northeast. This is consistent with the expected pattern of temperature in an El Niño winter. But the prediction of warmer than normal weather in the Southeast is not what we expect if we look only at El Niño. It also includes the effects of greenhouse warming, which is likely to overcome the cooler conditions that would be expected in the Southeast from El Niño alone. On the other hand, since there is not much long-term trend in precipitation, the precipitation outlook on the right shows a clear El Niño signal with wet conditions along the Gulf and South Atlantic coasts and dry conditions in the Northwest and to a lesser extent, in the Upper Great Lakes. In the Southeast, El Niño winters are expected to be cooler than normal because all the clouds associated with the rainy conditions keep daytime temperatures down.

What do we expect for this year?

Because the El Niño is coming on strong, I expect it to drive a lot of this year’s growing season climate. While it is still weak, it won’t have much impact on our regional climate variations, which makes summer difficult to predict. In that case, we look more towards the current conditions and trends to conclude that areas that are already experiencing drought are likely to get worse, and areas that are starting out wet may get a reprieve from drought conditions for a few months.

The biggest impact of an El Niño in the growing season is in how it affects developing Atlantic and Eastern Pacific hurricanes. In El Niño years, tropical systems in the Atlantic tend to be fewer in number and weaker because the strong jet stream aloft keeps tropical cyclone circulation from strengthening into tropical storms or hurricanes. In the Eastern Pacific, it is just the opposite, with more storms forming than usual. That can help feed moisture into the Southwest. Of course, it only takes one storm coming over your home and garden to cause tremendous damage, so you need to prepare for storms if you live in a hurricane-prone part of the United States or other Northern Hemisphere location.

By fall, the El Niño is expected to be well developed and areas where El Niño usually brings rain could see the wet conditions start earlier than usual. For farmers, that means harvest could be difficult if conditions are wetter than usual, and it might be hard to get that last cutting of hay. Winter could be drier than normal in the northern states since many of the rain-bearing storms will be farther south than usual, although you will certainly see some rain.

Wet rainy fall day, 1,Do1,Teach1, Commons Wikimedia

Deep sheet mulching is “bat-sheet crazy”

“Mimicking nature”

I just returned from one of my self-imposed retreats where I have no cell phone service nor internet. This means I can focus on writing without interruption. One of my projects this year is to publish a scientific critique of permaculture (stay tuned for that late 2023). Part of my process is to read popular permaculture publications and I am focusing on Gaia’s Garden.  Earlier I’ve posted some general critiques of the book (you can find them here, here, here, and here), but until yesterday I had missed a big, fat problem: a section labeled “The Power of Sheet Mulch” (pages 71-75 in the first edition).

Natural leaf mulch

First of all, let me state that part of permaculture philosophy is to follow nature in our gardening practices. There are few examples of sheet mulching in nature. The only one I can think of occurs in deciduous forests, where fallen leaves can create a sheetlike cover several inches deep. Combined with microbial activity and wetter soils, these sheets create low soil oxygen conditions. During the winter the leaves are broken down and by spring have degraded to the point that air and water movement have resumed enough to support plants as they break dormancy.

Old carpet is recommended as part of a permaculture mulch

In contrast, here’s what permaculture recommends. At the outset, let’s acknowledge that none of the practices discussed remotely resembles any natural process. Furthermore, there are no science-based citations to support the practices or the claims of success. It’s completely anecdotal.

A sidebar provides the methods and materials for constructing the “ultimate, bomb-proof sheet mulch.” Here’s a condensed step-by-step breakdown:

  1. “Soil amendments, depending on your soil’s needs” are added to the top of the soil before the sheet mulch is applied. How you determine your soil’s needs involves either “us(ing) a soil test or your own understanding of your soil’s fertility to guide the type and quantity of soil amendments.” These include “lime, rock phosphate, bonemeal, rock dust, kelp meal, or blood meal.”
  2. A “thin layer of high-nitrogen material” is placed on top of the amendments.
  3. Next we “…apply a layer of weed-suppressing newspaper or cardboard (or even cloth or wool carpet).”
  4. On top of the sheet mulch another thin layer of high-nitrogen materials is applied.
  5. Next we are to add “about 8 to 12 inches of loose straw, hay, leaves…” or any other bulk mulch materials recommended.
  6. Then we should add “an inch or two of compost” or “you can substitute manure or several inches of easily compostable material.”
  7. Finally “2 inches of…straw, fine bark, wood shavings…” or other listed “weed- and seed-free organic matter” adds the finishing touch.

So. Much. Stuff.

So let’s add this up: a half-inch or more of sheet material, an inch or more of high nitrogen material (from those two additions), 8-12 inches of bulk mulch, another 1-2 inches of compost (or several inches of the substitute), and 2 inches of “the finished look” materials. That’s at least 12 inches of wet (oh, each layer is sprayed down with water as it’s applied), poorly drained material on top of the soil.

I’m all for following nature in how we manage our gardens and landscapes. But deep sheet mulching isn’t natural. It’s bat-sheet crazy.

Sheet (mulch) cake, on the other hand, I could get behind. (Photo courtesy of Hayes Valley Farm)

You gotta know what to sow and what to plant: Veggies and Herbs

As a continuance of my Kenny Roger’s themed article last month on sowing and planting at appropriate soil temperatures, I thought this month I’d approach “Know when to sow ‘em, know when to plant ‘em” in a different way.  When it comes growing vegetables and herbs, many new (and even experienced) gardeners are confused as to which plants you should directly sow into the garden and which ones you must transplant. 

Of course, some of these recommendations might change based on where you are and your local climate.  These are general recommendations based on common practices in most of the U.S. Decisions can be easier to make if you know the reason WHY some things are started indoors and transplanted outside and some things are directly sown, so we’ll start there.

Why transplant?

For the most part, the crops that we start indoors (or purchase at the garden center) and transplant outside are things that either require a long time to reach maturity or require higher temperatures to germinate and thrive than are available outside in regions where these crops are not native. Starting indoors allows us to overcome shorter growing seasons and get those crops to mature in a timely manner.

Many of the warm season crops, such as tomatoes, peppers, and eggplant would likely not make it to maturity if they were directly seeded in the garden after the danger of frost has passed.  And while many cool season crops like the Cole crops (broccoli, cauliflower, cabbage, etc.) thrive when air temperatures are cool, they actually require warmer soil temperatures for germination and would be difficult to direct sow outdoors for a spring planting. In many parts of the country, cool season crops do much better as a fall crop since temperatures get cooler as the crops mature. This means that they should be sown or planted in July or August for most areas. Directly sowing of seed in the garden is technically possible at that time BUT there are many challenges including keeping the seedlings from drying out in the hot, dry summer weather.  So it is usually still easier to transplant, but you can start the transplants in pots in a protected outdoor space rather than indoors if needed. Keep in mind that several of the herbs don’t start well from seed, so you’ll need to buy transplants (which are usually started from cuttings) or take cuttings from an existing plant.

Why direct sow?

There are a number of crops that grow fast or easy enough that they can just be sown directly in the garden. My personal philosophy is that if it can be direct sown you don’t have to worry about the expense or trouble of starting plants indoors or the expense of buying individual plants at the garden center.  Crops like lettuce, beans, peas, corn, squash, and melons are typically very easily sown outdoors. Some folks might opt to start these inside or to buy starts to make it easier, but this is usually at an extra cost that isn’t necessary for success.

Of course, root crops like carrots, radishes, turnips, and beets aren’t easily transplanted because the process of transplanting can damage the root, which is the part you’re trying to grow.  Some herbs like cilantro don’t tolerate root disturbance well, so it is best to direct sow as well.

Knowing when to sow is important as well.  Cool season crops like lettuce, radishes, carrots, and other leafy greens and root crops can be sown well before last frost (see my article from last month, linked above). 

The other thing to keep in mind when direct sowing is that conditions outdoors aren’t as stable as those indoors, so you’ll have to monitor the weather for rapid swings of temperature and also make sure things stay appropriately watered. 

Some crops can go either way

While some crops like squash and cucumbers are easy to direct sow, there might be times when growers might prefer to start indoors (or buy starts) and transplant.  Crops like melons often require high soil temperatures to germinate, so in places where the soil temperature is slow to warm transplanting might be helpful.  Transplanting can also give the grower a leg-up on getting things to maturity quickly. Transplanting is most common for crops where you need a smaller number of plants (like squash and cucumber) but isn’t as practical for crops where you need larger numbers of plants like beans and peas. Keep in mind that crops like cucumbers and squash usually start pretty quickly and will be transplantable after just a few weeks – growing them indoors until they are bigger isn’t necessary and will not create an advantage to getting them to mature quickly.

What to transplant

  • Broccoli
  • Brussels Sprouts
  • Cabbage
  • Cauliflower
  • Celery
  • Collard Greens
  • Eggplant
  • Kale
  • Kohlrabi
  • Lavender
  • Oregano
  • Peppers
  • Rosemary
  • Tarragon
  • Tomatoes
  • Tomatillos

What to Direct Sow

  • Beans
  • Beets
  • Carrots
  • Cilantro/Coriander
  • Dill
  • Leeks
  • Peas
  • Radishes
  • Spinach
  • Sunflowers
  • Turnips

Which Can Go Either Way

  • Basil
  • Bok choi/Pak choi
  • Cantaloupe
  • Chard
  • Cucumber
  • Fennel
  • Lettuce
  • Melons
  • Mint
  • Okra
  • Onions
  • Parsley
  • Pumpkins
  • Watermelon
  • Squash
  • Zucchini

Sources

Master Gardener volunteers transplant tomatoes for the All America Selections trials in Omaha.

Spring Pruning

I think I have a pruning fixation. I take most opportunities that come along to write about pruning. I have not blogged yet about Spring pruning. It can be a useful way to achieve some pruning objectives. Like all practices it is not necessarily the method or timing of method of choice for all plants. Spring Pruning can have some specific impacts on development of deciduous fruit trees that may help in the home orchard.

Springtime may not be the most obvious time to prune–in fact springtime within the geographic context of this blog requires definition. For this discussion, springtime is the period during which buds are opening, shoots are elongating, flowers are pollinated, and fruit is set or is rapidly enlarging. These are changes in the tree phenology that are critical to fruit production. As you may recall from previous blogs on pruning there are some basic impacts that pruning has. Pruning is growth limiting. Pruned parts will grow less than unpruned parts. Spring pruning is an opportunity to regulate fruit retention.

Phenology is the growth stage of a tree and defines the period when Spring pruning can begin

Spring growth and tree phenology are not timed to be the same. Apricots will flower before or after peaches, plums, pears or apples. This can happen in different months depending on latitude of your garden. Spring is in set time back to another vegetative shootand Spring pruning is thus variable across location and species in your garden.

So why is pruning in Spring at all helpful? The main reason is to reduce the number of fruit that are set on a tree. Reducing fruit count will allow more sugar to enter fewer fruit increasing the size of remaining fruit and improving quality.
Pruning during bloom is risky, we don’t know what the fruit set will be until a few weeks later. Also changes in weather such as spring frosts, wind, or even hail and snow can destroy a crop in its juvenile stages and if you have already pruned, you have lessened your changes for fruit later. It’s best to wait until fruit have set, are growing, enlarging and that you are pretty sure the crop is under normal progression.

With a Spring prune I like to remove about half the set fruit. This would involve trimming the ends of branches (that have fruit) by 50 percent. You may still need to thin fruit later because the remaining fruitful stems you leave on the tree may have too many fruit to ensure quality. Thinning peaches to about one every six inches in late Spring, reducing pear and apple clusters to one fruit per spur and minor thinning of plums will suffice. Apricots usually need little thinning for adequate quality.

Another reason to thin in Spring is to reduce disease incidence. Peach leaf curl is usually well developed even as fruit is setting. The best control of peach leaf curl is with a dormant fruit tree spray prior to bud break. But, if you miss that opportunity to spray, pruning out the infected leaves and shoots will decrease the inoculum for next year. Dispose of the infested shoots in the trash (although correct hot-composting will likely kill the inoculum as well).

Peach leaf curl can be pruned out in the springtime if you miss your dormant spray

Spring pruning is not recommended in areas where there are frequent rains, bacterial diseases such as bacterial canker or when your trees are not vigorous and otherwise healthy. Pruning creates wounds that allow pathogens to enter the tree and a wise gardener will avoid pruning during warm showery weather. If conditions are dry and sunny, Spring pruning can be effectively used to slow growth and increase fruit quality for the coming summer harvest.

For more information on the science – and myths – behind pruning, Dr. Chalker-Scott and I published a peer-reviewed article on this recently.

Hasta la vista, La Niña!

Last April 30, 2022, I wrote a post about what a third year of La Niña meant for gardens. La Niña, you might remember, is an atmosphere/ocean phenomenon driven by unusually cold water in the Eastern Pacific Ocean (EPO) that shifts the jet streams that steer storm systems around the world. In La Niña winters in North America, it is often linked statistically to colder and wetter than normal conditions in northern parts of the United States and north into Canada and warmer and drier conditions in the southern tier of states in the US. Just a couple of weeks ago, NOAA announced that the long La Niña has finally ended and that we are now in a neutral period. In last year’s post, I described the difference between La Niña and the opposite climate phase, El Niño, and how they affect climate conditions around the world. So now you might be wondering how this switch to neutral conditions and then potentially to an El Niño later in the year will affect your gardens in the coming growing season.

Elfen-Krokus (Crocus tommasinianus), AnRo0002, Commons Wikimedia

How good was last year’s forecast?

A discussion of how accurate the forecast for last winter was can be found in NOAA’s ENSO blog. As you can read, the temperature forecast was much better than the precipitation forecast (as it usually is). That is not surprising because many causes of rain and snow occur on very small spatial scales from a variety of physical processes that are not always well-captured in our current climate models. You can hear a more detailed discussion of historical ENSO patterns by David Zierden, the Florida State Climatologist, in this 15-minute video for the March 2023 Southeast Climate Monthly Webinar starting at minute 28:35).

Two U.S. maps comparing predicted and observed 2022-23 winter temperature

As a result of the cold and snowy conditions in northern parts of the country, spring there has been delayed, and my friends in the Upper Midwest have only started to see daffodils and other early spring flowers, while in the Southeast, our azaleas and dogwoods are already in decline about a month earlier than usual (you can track this at the National Phenology Network website we’ve discussed before).

What happens next?

Now that La Niña has ended, we are in neutral conditions. That means it is difficult to predict the climate during the next few months because without La Niña (or El Niño) to give us statistical guidance on what climate to expect, almost anything can happen. The variations in climate in neutral seasons are caused by local variations, other interactions in climate on regional or global scales, and other factors that are not always well understood. In addition, we are in spring, which historically gives us the least trustworthy predictions for the coming seasons due to what is called the “spring predictability barrier.” That means that while we think we are likely to swing into an El Niño in the next few months, the atmosphere might have other ideas and could keep us in neutral conditions for quite a while before we switch to an El Niño.

This year, we are already getting signs in the Eastern Pacific Ocean that a switch to El Niño will come quickly. The water near the coast is already quite warm and the warm pool is starting to stretch out to the west. In other words, El Niño-like conditions are already present in the EPO, but have not lasted long enough yet for an official El Niño to be declared. That usually takes several months of monitoring to make sure this is not just a short-term change.

https://iri.columbia.edu/wp-content/uploads/2023/03/figure1.png

What do neutral and El Niño conditions mean for the Northern Hemisphere growing season?

Usually, ENSO conditions do not strongly affect the NH summer climate. That is because both La Niña and El Niño are strongest in the winter months and tend to weaken or disappear in the summer. Local conditions including soil moisture variations such as drought, ocean temperature variations, and local weather systems have a much bigger impact on growing season weather than ENSO does in most areas.

However, the ENSO state does have one strong influence. That is in the tropical activity in the Atlantic and Eastern Pacific Oceans. When neutral conditions or La Niña conditions occur, the jet stream aloft is weak and it is easier for tropical waves to develop into tropical storms and hurricanes, so neutral and La Niña seasons tend to be more active and have more named storms. When an El Niño occurs, the jet stream is unusually strong and that keeps tropical waves growing vertically into strong storms, so the number of tropical storms and hurricanes in the Atlantic is usually lower in years when an El Niño is occurring. Of course, it only takes one storm (Hurricane Andrew in 1982 was in an El Niño year) to cause tremendous damage if it hits somewhere vulnerable. In contrast, the storm activity in the EPO increases in El Niño years due to the pool of warm water there.

a graphic showing el nino weather pattern over nation

This year, the likely storm activity may be more tied than usual to the ENSO state. If we see a quick switch to El Niño after just a few months of neutral conditions, the Atlantic may be most active early in  the season, while storms later in the season will be suppressed. By comparison, in the western US where some moisture enters the country through EPO storm activity, you may see an increase in thunderstorms that are fed by the water vapor entering the country from the storms in the EPO.

What does this mean for your gardens?

If you live in an area that normally gets rain from Atlantic tropical activity, even if it is not from actual tropical cyclones or hurricanes, you can probably expect drier conditions this year, or at least more variable rainfall from less organized systems as more precipitation will be produced from local influences. El Niño does tend to delay the onset of the Southwest Monsoon, so that could be something to watch next year, although it may not have much impact this year. In Texas, the switch to neutral conditions means rain in April through June is more likely, which would be great for avoiding drought. If you live in an area that does not receive much moisture from the tropics, it will be hard to make a good forecast because the statistics just don’t give much guidance. We do know that globally, El Niño years tend to be very warm, so it is likely that 2023 may be one of the warmest, if not THE warmest, since global records began in 1880 due to the long-term rise in temperature from greenhouse warming. Warmer weather will mean a longer growing season, more hot days and nights, more humid conditions (unless a drought occurs), and more diseases and pests that thrive on the warmer conditions.

What do we expect next winter?

If you like to plan far ahead, you can see seasonal forecasts from NOAA’s Climate Prediction Center at Climate Prediction Center – Seasonal Outlook (noaa.gov). If you are not from the United States, your own country’s weather service may provide similar outlooks for your region. Here in the US, we are likely to see wetter and cooler conditions in the southern US as the jet stream steers storm systems over us (days will be cooler because of the clouds, but nights won’t necessarily be colder than usual since clouds trap nighttime heat). In northern states, warmer and drier conditions will be more likely, and that could mean an earlier start to the growing season next year. Now that something to look forward to if you are a gardener!

Tulipa “El Niño” 2015, Retired electrician, Commons Wikimedia.

My “Dirty Dozen” garden products

Image courtesy of Rotten Tomatoes

“Dirty Dozen” is one of those short, alliterative phrases that’s easy to remember and fun to use. In today’s post, I’m applying it to garden products whose production or use can be damaging to the health of ecosystems, environments, and even humans. How many of these products are in your garden shed, or appear in ingredient lists of other products? Each short description below has one or more links to additional information. After you count them up, see how you rank on the Charlotte Scott Meme-O-MeterTM

Product manufacture damages ecosystems

A protected peat bog in British Columbia

Peat moss. Peat moss bogs are slow-growing ecosystems that store vast amounts of carbon. Removing peat moss destroys these ecosystems (which can take centuries to regrow) and releases C02 into the atmosphere. Do a little experimentation with sustainably sourced or locally available crop residues and see if you can find a more environmentally friendly substitute.

Kelp forest at low tide. Image courtesy of NOAA Photo Library

Kelp. Kelp, or macroalgae, are the basis of intertidal and subtidal food webs. Removal of these plants creates underwater deserts where little life can be found. Restoration can be done, but it’s a slow and expensive process. Ask yourself why you think you need kelp and compare this to the facts.

There are lots of sources of manure on the internet…

Bat guano. Seems like a reasonable use of a waste product, right? Nope – and Dr. Jeff Gillman explained why in a post more than a decade ago. If you want a sustainably produced, manure-based fertilizer, you can find many options at garden centers.

Products whose use damages garden and landscape soils

Rubber mulch. Look closely and you can see bits of metal from steel-belted tires.

Rubber mulch.  Recycling used tires is a good idea; grinding them up and putting them on top of your living soil, not so much. There are much better mulch choices out there.

Landscape fabric with healthy crop of weeds

Landscape fabric. Landscape fabric does not control weeds, nor is it permeable once installed. It’s a sheet mulch that restricts water and air movement between the soil and the atmosphere. Weeds will quite happily colonize the surface while the roots of desirable plant struggle for water and oxygen below the barrier.

Black Death in a sad landscape

Plastic mulch. There is nothing worse (see chart in this link) you can put on a living soil unless your intention is to kill everything under it. You may see it used in agricultural production, but that doesn’t make it a good choice for your gardens and landscapes. Again, there it a much better alternative to this and all other sheet mulches.

Lots of claims about Epsom salt…but does your soil need magnesium?

Epsom salt. Would you be so excited about buying this stuff if it was correctly labeled as magnesium sulfate? That’s all it is – an inorganic chemical. Despite its soothing name, Epsom salt is not a cure all for anything except a magnesium deficiency in the soil. Overuse can create nutrient imbalances in soils.

Products whose use damages plants and plant-associated microbes

Always check that NPK value before you buy anything

Phosphate fertilizer. The most overused nutrient in home gardens and landscapes, and one that can cause iron deficiency in plants. The only time you should add anything containing phosphate – including compost or other rich organic material – is if you have a soil test indicating a deficiency.

DIY garden remedies. Self-proclaimed gardening experts come up with all kinds of home-made potions as safer alternatives to conventional fertilizers or pesticides. There are good reasons that both fertilizers and pesticides are regulated at state and/or national levels: it’s the only way you can know exactly what the active ingredients and when, where, and how to apply these chemicals. To follow some “chemical-free” recipe from the internet is playing Russian roulette in terms of collateral damage to soils and non-target organisms.

Another fine Black Death product

Wound dressings. Unfortunately, many gardeners don’t understand that plants and people respond differently to injury. While antibiotic dressing and bandages are good for healing our nicks and cuts, trees have a completely different response. Slathering black goo or paint over tree wounds is the last thing trees need to seal damage naturally.

Product whose use can be harmful to human health

Read the label before purchasing a hydrogel

PAM hydrogels. PAM (polyacrylamide) hydrogels have limited usefulness in home gardens and landscape – worse, they have to potential to injure people and pets. (There is also a list of references used in the linked article.) After these same materials are used in labs for gel electrophoresis (used for DNA analysis, for example), their disposal is generally regulated. No such regulations exist for using them in the landscape. Hydrogels based on starch or other natural polymers are fine – but avoid anything that contains “acrylamide” or “acrylate” on the label. Better yet, use a well-chosen mulch to absorb and release water to the soil.

Time to take the quiz!

You score zero: Well, well!
You score 1-3: Maybe you’ve been a part of this community for a while or maybe you’re just acutely aware of sustainable products and practices. Either way, the Garden Professors thank you!
You score 4-6: So maybe you recently broke up with your local garden center and are reevaluating some of the products they recommend. Stay strong!
You score 7-9: Oh, bless your heart. Let’s talk.
You score 10-12: So you take the phrase “scorched Earth” pretty seriously, huh?

All jokes aside, sustainability and gardening require constant adjustment and learning. You came here, you read through this list, and you are thinking critically about your practices.

Don’t be a garden gambler: You’ve got to know when to sow ’em, know when to plant ’em

For many gardeners around the US (and the northern hemisphere) the weather is warming up for spring planting season and many are itching to get out in the garden. But when is the right time to plant those veggies and flowers and not gamble on their success? Just like Kenny Roger’s character in The Gambler, knowing when to do something is important (this is where I’ll end the cheesy comparison – you’ve just got to come up with a catchy title sometimes).

I’ve spoken previously on this blog about understanding frost dates, which is important for planting warm-season crops like tomatoes, peppers, and cucumbers that won’t survive a frost. (You can read that article here.) But another temperature factor we must consider, especially for cool season plants that we plant BEFORE last frost is the soil temperature.

Soil temperature is especially important for direct sowing seeds in the garden, but it can also affect the success of transplants planted in the garden. For transplants, having an appropriate soil temperature supports root growth and development and helps plants get established faster.

Many warm season plants, especially plants like peppers, won’t establish easily or thrive unless soil temperatures are sufficient for root growth.

Why soil temperature matters for seeds

For direct sowing of seeds, soil temperature has a major effect on the speed of germination, which also affect the success rate of germination. Each different seed has a different optimum temperature for germination. If the soil temperature is below, or above, that level then germination can be slowed down. Slow germination can decrease germination rates through a few different avenues:

  1. Germinating seeds are vulnerable to infection or decomposition by fungi and bacteria in this soil. When starting seeds indoors, this can be limited by using a sterile seed starting mix. But when direct sowing outdoors, there are any number of fungi and bacteria in the soil that will decompose a struggling seed/seedling. Some seeds sold for large-scale production will have a coating of fungicide on them that will provide a few weeks worth of protection. You won’t likely find this on home garden seeds, but it might appear if you buy seeds from a farm supply store or a catalogue that caters to farm-scale producers.
  2. Seeds have a finite amount of stored energy. Once germination begins, the respiration rate of the embryo in the seed radically increases. If germination is slow, the embryo can expend the stored energy before the seed leaves emerge and start producing energy to support the developing seedling. (This also occurs if you plant the seed too deeply).

Below is a graphic I made for Nebraska featuring the best soil temperature range for major vegetable crops (notice how it also lines up with last frost dates). Just ignore the info on frost dates for Nebraska, unless you live in Nebraska.

Most of the resources you’ll find on soil temperature and germination are for vegetable crops. If you are trying to start seeds of ornamentals, you’ll likely have to find the information yourself. The seed packet will give you some indications of when to sow (before/after frost, or maybe in the fall for overwintering to break dormancy) and you can search online for guidance for specific plants. For info on starting seeds indoors, check out this previous article I wrote on the subject.

How to measure soil temperature

Of course, the tried-and-true old fashioned way is to use a thermometer. You can find a soil thermometer at many garden centers and retailers. You’ll want a soil thermometer because the ones for your kitchen likely don’t have the right temperature range – we’re measuring well below the temperature of a roasted chicken here. Instert the thermometer two to three inches into the soil and wait several minutes for the temperature arm to adjust before reading. Also keep in mind that temperatures fluctuate with the weather and throughout the day depending on temperature and the amount of direct sunlight hitting the soil surface – so you want to measure a few times to make sure the temperature is staying within the right range.

Now, the new technological way is to find a soil temperature monitoring station online. Soil temperature monitoring is a common feature of many weather stations these days and data is more available than ever. Many university extension services or ag research centers compile soil temperature maps for use by farmers and this data is also often accessible through NOAAA or weather.gov. In Nebraska, we have an extension program called CropWatch that provides average daily and weekly soil temperatures year round. We also have a weather station with soil temperature probes at our extension office (perks of having a meteorologist as a master gardener volunteer) and we (and our master gardeners) use it when providing information to clients. It can be hard to find a resource that provides soil temperatures nation-wide to share in the patchwork of private and public stations (and the National Weather Service site can be notoriously hard to navigate). There are a few online resources from the ag industry that provide a country-wide system, like this one.

And now its time for me to walk away, time for me to run

Unlike The Gambler you don’t want to wait until after the plantings done to count your money, er, check the temperature. Remember that knowing the soil temperature, whichever method you use, will help your plants succeed in the garden. If you do, your garden could pay out bountiful winnings all through the season.

By knowing the soil temperature, your seeds will turn into a sure bet. Source: Wikimedia Commons