Regular blog readers will remember that we moved to my childhood home a few years ago. With an acre or so of landscape I finally have enough room to put in a vegetable garden. My husband built a wonderful raised bed system, complete with critter fencing, and we’ve been enjoying the fresh greens and the first few tomatoes of the season.
We filled these raised beds with native soil. During a porch addition I asked the contractor to stockpile the topsoil near the raised beds. The house was built almost 100 years ago and at that time there were no “designed topsoils” (thank goodness) – soil was simply moved around during construction. Some of this soil had been covered by pavers and the rest had been covered with turf. [You can read more about designed topsoils in this publication under “choosing soil for raised beds.”] There had been no addition of nutrients for at least 7 years so I was confident that this was about as natural a soil as I could expect.
I’ve always advised gardeners to have a soil test done whenever they embark on a new garden or landscape project, so before I added anything to my raised beds I took samples and sent them to the soil testing lab at University of Massachusetts at Amherst (my go-to lab as there are no longer any university labs in Washington State for the public to use).
What I already knew about our soil was that it’s a glacial till (in other words it’s full of rocks left behind by a receding glacier). The area is full of native Garry oak (Quercus garryana), some of which are centuries old. The soil is excessively drained, meaning it’s probably a sandy loam. And that’s about all I knew until my results came back.
Because nothing has been added to this soil for several years, and because I had removed all of the turf grass before filling the beds, I assumed that the organic matter (OM) would be quite low. Most soils that support tree growth have around 3-7% OM. Hah! Ours was over 12%! All I can figure is that centuries of leaf litter has created a rich organic soil.
So here’s lesson number one: Don’t add OM just because you think you need it. Too much OM creates overly rich conditions that can reduce the natural protective chemicals in vegetation. This means pests and diseases are more likely to be problems.
I was pleased to see our P level was low. First soil test I’ve ever seen in my area where P was below the desirable range! Does that mean I’m adding P? No – because there is no evidence of a P deficiency anywhere in the landscape. And my garden plants are growing just fine without it.
Lesson number two: Just because a nutrient is reportedly deficient, look for evidence of that deficiency before you add it. It’s a lot easier to add something than it is to remove it.
Likewise, our other nutrient values are just fine, and I was pleased to see that lead levels were low. Given that this is an older house that had lead paint at one time, and given the fact that the soil being tested was adjacent to the house, I was prepared for lead problems.
However – we do have high aluminum in the soil. Exactly why…I don’t know. Perhaps the soil is naturally high in aluminum? There’s no evidence that aluminum sulfate or another amendment was ever used. In any case, that was an unexpected result that does give us some concern for root crops. I’ll be doing some research to see what vegetables accumulate aluminum.
Finally, note our pH – 4.9! This is completely normal for our area, which is naturally acidic. In addition, the tannic acid accumulation from centuries of oak leaves has undoubtedly pushed the pH even lower. Are we going to adjust it? Again, no. There is no evidence of any plant problems, and even our lawn is green. Why would we adjust the pH if there is no visual evidence to support that?
Which leads to lesson number three: Don’t adjust your soil pH just because you think you should. If your plants are growing well, the pH is fine. Plants and their associated root microbes are pretty well adapted to obtaining the necessary nutrients. If you have problems, don’t assume it’s a pH issue. Correlation does not equal causation! You’ll need to eliminate all other possibilities before attempting to change your soil chemistry. And remember it is impossible to permanently change soil pH over the short term. Permanent pH changes require decades, if not centuries of annual inputs (like our oak leaves).
Will I test my soil again? Probably not. I have the baseline report and since I don’t plan to add anything I don’t expect it to change much. If I had a nutrient toxicity I would retest until the level of that nutrient had decreased to normal levels. But with everything growing well, from lawn to vegetables to shrubs and trees, there really is nothing to be concerned about.
Lesson number four: Unless you have something in your soil to worry about, don’t.
“Will my peppers continue to ripen? How about my eggplants?” It is common knowledge to most gardeners (and home cooks) that tomatoes will ripen on the kitchen counter, as will bananas and several other fruits. You know that one day your bananas look perfectly ripe and the next they’re a brown mush But does this work for all fruits? We often get questions about whether specific fruits will continue to ripen after picking. And the answer is….. it depends.
One of these fruits is not like the other
The answer as to whether a fruit will continue to ripen after harvest depends on which one of two groups it falls into. These groups are climacteric and non-climacteric fruits. In short, climacteric fruits are the ones that will continue ripening after harvest and non-climacteric fruits are ones that don’t ripen after harvest.
This refers to the “climacteric phase” of fruit ripening where there is an increase in the gaseous plant hormone ethylene and an increase in respiration, which drives the ripening process. It is the climacteric fruits that will keep ripening once they’ve been harvested, thanks to ethylene. The only stage of maturity for non-climacteric fruits after harvest is…..compost.
As long as you’re green, you’re growing. As soon as you’re ripe, you start to rot. -Ray Kroc
Almost all fruits produce ethylene, but non-climacteric fruits produce them at much lower levels and do not rely upon it as the main driver of ripening. I’ll go into a bit more detail in a bit, but first – which fruits are climacteric and which are non-climacteric?
Common Climacteric Fruits
Common Non-Climacteric Fruits
Brambles (raspberry, blackberry, etc).
Citrus (oranges, lemons, limes, etc.)
Melon (including Watermelon)
Cantaloupe / Muskmelon
Squash (summer and winter)
*Some evidence of climacteric ripening in hot peppers
The ripening process
Ripening is genetically programmed – meaning that it is highly dependent on processes that are regulated by genes and it specific to each species. Parts of the process are started and stopped due to the transcription and translation of genes, which are in turn controlled by signals such as chemical compounds, physiological stages of the plant, climate, and so on. These ripening processes have a lot of end results – sugars accumulate in the fruit, pigments develop, some compounds that have pleasant flavors develop while others that are unpleasant are broken down, some of the pectins in the fruit break down to make it softer, and on and on.
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.
The dependence on ethylene for a vast majority of fruits to ripen has been used by farmers and the food industry for a long time to keep climacteric fruit more stable for shipping. These fruits are harvested “green” before they ripen and shipped unripe since they are much firmer and much less likely to get damaged in transit. These days, bananas, tomatoes, and other climacteric fruits are likely to be given a treatment that temporarily inhibits the ethylene response before harvest or shipping to extend their shelf life further. Once they’re close to their final destinations they’ll either be allowed to ripen on their own or given a treatment of ethylene to speed back up the ripening process.
What we gain in shelf-life and reduced food waste we do lose in a bit of flavor. Since the fruits are no longer attached to the plant when they ripen they don’t have the chance to transport more sugars and flavor compounds from the mother plant. So “vine ripened” fruits do have a bit more sweetness and flavor than those that are picked green. Having just gotten back from Rwanda, a country where bananas are a common staple food I can attest that the ones that ripen on the plant are much sweeter than those we get shipped in to the US – you know, the ones that will ripen next week sometime if you’re lucky. There were even some in our group that don’t care for bananas here that loved the ones we had at breakfast every morning.
One possible direction for biotechnology is the engineering of plants to alter or eliminate the ethylene ripening response to reduce food waste and spoilage. Since many genes that are responsible for ethylene production such as enzymes that catalyze the production of ethylene precursors, or proteins that serve as ethylene receptors have been identified, work is being done to develop delayed ripening by altering or knocking out these genes in a variety of crops.
“Can I use manure to fertilize my garden?” That’s a common question we get in Extension and on the Garden Professors page. The answer is absolutely, but there’s a “but” that should follow that answer that not everyone shares. And that is…but for fruits and vegetable gardens the manure you apply could be a potential source of human pathogens that could make you or your family sick. There are procedures and waiting periods you should follow to reduce the potential risk to human health from pathogens in manure and other animal products.”
First, application of manures to garden and farm production spaces is a good use of nutrients and provides a way to manage those nutrients to the benefit of growers and the environment. Using the concentrated nutrients in the manures to grow crops reduces what washed downstream in the form of pollution. In addition to adding nutrients to the soil, application of manure and other animal byproducts (bone meal and blood meal, for example) add organic matter to the soil, which improves soil texture, nutrient retention and release, and supports beneficial microorganisms.
For organic production, both in home gardens and on farms (certified organic or not), manure and animal products are an important input for fertility. For the most part, manures offer a more concentrated (higher percentage) of nutrients by weight than composts composed only of plant residues, so less is usually needed (by weight) than plant composts to apply the same amount of nutrients.
While the nutrient levels of manures and composts can be highly variable, there are some general ranges that you can use to plan your application based on the needs you find in your soil test. (And you should be doing a soil test, rather than just applying manure or compost willy-nilly. Just because the nutrient concentrations are lower than a bag of 10-10-10, you can still over-apply nutrients with composts and manures).
So what are the hazards?
As you’ve probably realized from bathroom signs and handwashing campaigns, fecal material can carry a number of different human pathogens such as E. coli and Salmonella. The major risk around application of manures to edible crops is the possible cross-contamination of the crop with those pathogens. The number one hazard leading to foodborne illness from fresh produce is the application of organic fertilizers – mainly manure, but also those other byproducts like blood meal and bone meal. Add in the fact that the consumption of raw fruits and vegetables has increased over the last decade or more, and you’ll soon understand why Farmers who grow edible crops must follow certain guidelines outlined in the Food Safety Modernization Act (FSMA, which you’ll hear pronounced to as fizz-mah) to reduce the potential risk that these pathogens pose to people who eat the crops. Right now, only farms with a large volume of sales are required to follow the guidelines, but smaller producers are encouraged to follow them as best practice to reduce risk and liability. And while there isn’t a requirement for home gardeners to follow the guidelines, it is a good idea to understand the risks and incorporate the guidelines as best practice. It is especially a good idea if the produce is being eaten by individuals who are at higher risk of foodborne illness – young children, the elderly, or those who are immunocomprimised.
The recommendations are also suggested when there’s contamination from unexpected or unknown sources like when vegetable gardens are flooded (click here for a recent article I wrote to distribute after the flooding in Nebraska and other midwestern states).
Recommendations to reduce risk
As previously stated, while these recommendations have been developed for produce farmers, research showing the potential hazards of applying manures means that it is a good idea for home gardeners to understand and reduce risks from their own home gardens.
The set of guidelines outlined by FSMA cover what are called Biological Soil Amendments of Animal Origin (BSAAO – since we government types love our acronyms). Here’s the “official definitions” used in the rules for produce farming:
A Biological Soil Amendment is “any soil amendment containing biological materials such as stabilized compost, manure, non-fecal animal byproducts, peat moss, pre-consumer vegetative waste, sewage sludge biosolids, table waste, agricultural tea, or yard trimmings, alone or in combination”.
A Biological Soil Amendment of Animal Origin is “untreated: cattle manure; poultry litter; swine slurry; or horse manure.”
For BSAAO (we’ll call it raw manure), manure should only be applied to the soil and care should be taken not to get it on the plants. There’s also a waiting period between applying the manure and when you should harvest the crop. The length of the waiting period depends on whether the edible part of the crop comes in direct contact with the soil. Right now the USDA is still researching the appropriate waiting period between application and harvest, so the general recommendation until then is to follow the standards laid out in the National Organic Program (NOP) standards. Research shows that while pathogens may break down when exposed to the elements like sun and rain, they can persist for a long time especially in the soil.
For now, here are the recommendations:
For crops that contact the soil, like leafy greens (ex: lettuce, spinach, squash, cucumbers, strawberries) the suggested minimum waiting period between manure application and harvest is 120 days.
For crops that do not contact the soil (ex: staked tomatoes, eggplant, corn) the suggested minimum waiting period between manure application and harvest is 90 days.
For farmers following FSMA, the waiting periods could change when the final rule is released – some early thoughts are that it could increase to 9 – 12 months if the research shows a longer period is needed.
What about composted manure? Is it safe? The guidelines indicate that there isn’t a waiting period between application of manure that has been “processed to completion to adequately reduce microorganisms of public health significance.” But what does that mean? The guidelines lay out that for open pile or windrow composting the compost must be maintained between 131°F and 170°F for a minimum of 15 days, must be turned at least 5 times in that period, must be cured for a minimum of 45 days, and must be kept in a location where it can’t be contaminated with pathogens again (animal droppings, etc). Farmers have the added step of monitoring and thoroughly documenting all of the steps and temperatures. Now we know that that’s a bit of overkill for home gardeners, but suffice it to say that the cow manure that’s been piled up to age for a few years that you got from the farm down the road doesn’t meet that standard.
“Aged” manure ≠ “processed to completion to adequately reduce microorganisms of public health significance.” So unless you know for sure that you’ve reached and sustained the appropriate temperatures in your compost, you should assume that it would be considered a BSAAO subject to the 90/120 waiting period. Bagged manure you buy at the garden center is likely to be composted “to completion” or may even have other steps to reduce pathogens like pasteurization. Sometimes the label will indicate what steps have been taken to reduce pathogens, or even state that it has been tested for pathogens.
The recommendations also specifically mention compost teas and leachates (a topic we handle with much frequency and derision here at the GPs, since there’s not much science to back up their use and I mention here with much trepidation). For the sake of food safety, any tea or leachate should only be applied to the soil, not the plant. And for home compost that doesn’t even contain animal manure the 90/120 day waiting period should still be observed in most cases since some of what goes into home compost is post-consumer. Since we put pieces of produce in there that we’ve bitten from or chewed on (post-consumer), plus some animal origin items (eggshells) there’s the potential that we could contaminate the compost with our own pathogens – and the environment is perfect for them to multiply.
The Bottom Line
While these guidelines and rules for farmers may just be best practice recommendations that we can pass on to home gardeners, common sense tells us that taking precautions when applying potential pathogens to our edible gardens. An ounce of prevention is worth a pound of cure, especially when were talking about poop.
Whether you’ve already got seedlings growing away or getting ready to start your annual indoor seed starting, one of the important factors in seed starting is light. (Last month I covered heat, which you can see here). Questions like “Do I need to use supplemental light or can I use a window?” and “What kind of light do I need to use?” are ones we often get from gardeners – new and seasoned alike. So I thought I’d take a little time to talk about light – the factors that are important for plant growth some ways that you can make sure you’re providing the right kinds and amounts of light to your new seedlings. Keeping these ideas in mind can help you choose lights for your seeds starting (or other plant needs), whether it is a simple shop light ballast from the hardware store, a pre-fab light cart system, or even higher-tech LED system.
Plants require light for several of their functions, most importantly the process of photosynthesis. The green pigments in plants (Chlorophyll A and B) act as receptors, gathering electrons from the light to use as an energy source to manufacture glucose, which is stored in the plant in a number of ways and then ultimately broken down in respiration to release energy to support plant functions. There are three aspects to light that gardeners should keep in mind for supplemental lighting: quality (color), quantity (brightness/intensity), and duration (day/night length).
Duration is a relatively simple concept when it comes to seeds starting and light set-ups. Gardeners will want to try to mimic the natural environment that will be provided by the sun. For the most part, aiming for 16 hours of light and 8 hours of dark is standard. This gives the plant sufficient light, but also provides a rest period which can be important for plant functions. Most gardeners find it handy to invest in timers to turn lights on and off, rather than trying to remember to do it themselves. This can be a simple on-off set up from the hardware store (after-holiday shopping can be a good way to pick them up on sale in the string light section) to something more elaborate from grower suppliers. Duration could be more important if you’re doing longer term growing beyond seeds starting, as day length affects initiating of flowering in some plants.
Intensity refers to how bright the lights are. Some lucky people have big windows with lots of bright light for starting seeds, but even for them intensity (and duration) may not be enough during the shorter, grayer days of winter. Growing in bright windows can sometimes be a challenge because the light is coming from the side rather than above, so plants often grow toward the window and need to be rotated. Supplemental light can increase intensity and lengthen duration, even for plants grown in windows.
Most commonly, light bulbs are sold by wattage as a measure of their energy (light) output. Standard tube florescent lights are generally around the 40 Watt level, but some of the full spectrum plant lights come in 54W options. If you can find it, the higher wattage can make a big difference in the intensity of light and thus the production of your plants. Even at the higher wattage, you’ll want to get a ballast that holds at least two bulbs (and some grow light ballasts hold more). You can further control the intensity of light reaching your plants by increasing or decreasing the distance between the plants and the lights. This is why the pre-made plant carts have a chain or other mechanism for you to raise and lower the lamps. For fluorescents, lights are sometimes lowered to around an inch above the canopy of the lights. For high intensity LEDs, the distance may need to be more. (If you’re using lights for long-term growth of, say houseplants, you’ll have to experiment with the distance to meet the intensity needs of the plants – closer for high light plants and farther away for low light plants).
Light Quality: The Rainbow Connection
Sunlight, or white light, is composed of all of the colors of the spectrum. Think back to art class and our friend ROY G BIV – the colors of the rainbow. There’s also parts of the spectrum that we don’t see like ultraviolet and infrared. For photosynthesis, plants mostly use light in the red and blue spectrum (referred to as Photosynthetic Active Radiation, or PAR), though almost all of the colors have some sort of effect or function on plants. Blue light has a role in promoting vegetative growth in plants, while red has a role in promoting flowering.
For most applications, supplemental light for seed starting or other indoor growing should be full-spectrum. You can achieve this in a variety of ways – buying specific full-spectrum plant light bulbs is the best, but you can buy non-plant specific full spectrum bulbs as well. For small-scale home growers and beginners, it can be as simple as buying a shop light ballast at the hardware/box store with a full spectrum bulb. For more intensive or large-scale growers, there are lots of sources for higher-end, full spectrum grow lights that you can buy from specialty garden retailers, but these are often more than what home gardeners starting seeds indoors need.
Fluorescent vs LED
These days you might be presented with a choice of lights – fluorescent vs. LED. There are some positives and negatives to each. While they have a higher up-front cost, LEDs use much less energy than fluorescents and can save money over several seasons of use. The reduced energy usage also means there’s less energy loss in the form of heat, which can be a positive if you are always struggling with creating excess heat that burns your plants, but a negative if you’re relying on that heat to help keep the temperatures up (see my article from last month on heat and seed starting) or have issues with drying out your growing media. Fluorescents on the other hand can be more affordable up-front, but have a higher energy usage that will result in higher electric bills over time.
You might have noticed in your searching or in visiting some growers that LED lights for plant growth come in either white (full spectrum) or a red/blue combination which end up giving a purple light. Since LEDs give a larger control over the spectrum of light, growers, especially larger scale intensive operations, use these red/blue combinations as a means to add further energy efficiency since it is the blue and red spectra that are the photosynthetic. By eliminating the spectra that are largely reflected rather than absorbed, less energy is used. This is useful in hydroponic and vertical farming systems where short-term crops are being grown quickly and where profit margins can be slim.
You can read (and listen to) more about light in the Joe Gardener podcast and article on seeds starting I was interviewed for last year with Joe Lamp’l.
However, research has emerged in the last few years that expanding the spectra of light in LED systems increases production. Research has shown that incorporating green LEDs significantly increases production over just red/blue LEDs (some of that research was by Kevin Folta, who is one of the leading science communicators on biotechnology). While green plants largely reflect rather than absorb green light, it does have some effect on plant functions. (Research also shows that adding the green makes the light appear a little more natural to workers in facilities like greenhouses and makes it easier to see issues with the plants – the purple of the red/blue systems washes out the plants and makes it hard to see differences in leaves like diseases).
So if you’re looking at LEDs for seeds starting, and especially if you’re looking at them for longer term indoor plant growing, stick with full spectrum or explore one of the LED systems that incorporates green. Though don’t be afraid to experiment with the colorful LED options – I have a small red/blue system to supplement light to my office potted lime. The key is to experiment and shop around – every gardener’s need for supplemental light is different and the solutions to those needs are different. Don’t be afraid to start small with that shop light from the hardware store before working your way up – especially if you’re just starting a small amount of seeds in the spring.
In most parts of the country it is time to dust off the seed starting trays, pick out your favorite seeds, and get a little plant propagation going on. There’s definitely a lot of science (and perhaps a bit of art) to successful seed starting. While the process starts (and relies on) the imbibition of water, one of the biggest factors that affects the success, efficiency, and speed of seed germination and propagation is temperature. Germination relies on a number of chemical and physical reactions within the seed, and the speed and success of those reactions is highly temperature dependent. Respiration, where the seed breaks down stored carbohydrates for energy, is probably the most notable process involved that is temperature dependent (source). Think of it in terms of a chemical reaction you might have done back in your high school or college chemistry class – there’s an optimum temperature for the reaction and any lower and higher the reaction might slow down or not happen at all.
Thinking of it this way, seeds and germination are just like Goldilocks and her porridge – there’s too hot, too cold, and “just” right. Seeds are the same way – there’s a “just right” temperature for germination. The seeds of each species has a different optimal temperature for germination with a range of minimum and maximum temperatures for the process.
Why is important that seeds are started at their optimal temperature?
The optimal temperature is the one at which germination is the fastest. This may seem to only have consequences for impatient gardeners, but slower germination speeds increase the days to emergence for the seeds, which in turns means that the seeds and seedlings have a greater chance of failure. The early stages of germination are when seedlings are most susceptible to damping off, which can be caused by a number of fungal pathogens (Fusarium spp., Phytophthera spp., Pythium spp., etc.) that basically cause the seedling to rot at the soil level. These pathogens (as well as decomposers in some cases) can cause seeds to rot or decompose before emerging as well. That’s why you’ll sometimes see seeds that are slow to germinate (or traditionally direct sown like corn, beans, and peas) treated with those colorful fungicides. The fungicide gives the seed and seedling a little bit of protection (for a week or so, depending on the product), which is handy if you accidentally sow them before soil temperatures are optimal or if the species is slow to germinate.
If emergence is really slow, there’s also the possibility of stunting or failure due to exhaustion of the stored carbohydrates that the seed relies on until it begins photosynthesis. So the closer to the optimal temperature the seed is, the faster the emergence and the highest percentage of germination success.
What does this mean for home gardeners?
Whether you are starting seeds indoors or direct sowing outdoors, knowing the germination temps can help increase your likelihood of success. You can find a variety of resources for the optimal germination temperature for your selected crops. In general, most warm season plants, like tomatoes, peppers, and summer flowers are in the 70-80 °F range. This is why most of the warm season crops are started indoors – so temperatures can be controlled to higher levels.
Many of the cool season crops germinate at much lower temperatures, which means many of them can be directly sown early in the season rather than started indoors. Crops such as spinach, lettuce, and other leafy greens have these lower germination temps and typically perform better if germinated at lower temps.
It should be noted that this is for the soil temperature, not the air temperature. If you’re starting seeds in your home, most people don’t keep their homes in the 75 – 80 degree range in the winter. Many commercial operations use warmed tables or beds for seed starting, rather than heating the whole facility to the necessary temp – it would be expensive. For home growers, supplemental heat mats can help increase soil temp without having to heat a whole room. In a pinch, you can even clean off the top of your fridge and keep seedlings there. It is higher up in the room (heat rises) and most refrigerators create some amount of external heat as they run.
For any seeds that you’re direct sowing outdoors, whether they require higher or lower germination temperatures, you’ll have more success if you plan your sowing around soil temperatures rather than calendar dates (planting calendars can be good for estimation, though). Investing in a soil thermometer can offer detailed information on the specific temperatures in your garden soil. Or, if you have a good weather station nearby many of them have soil temperature probes that could give you a good idea of what the soil temperatures are in your region.
But don’t let the cool/warm season crop designation fool you – the Cole crops like cabbage and broccoli actually have an optimal germination temperature on the warmer side, but grow better in cooler temperatures to keep them from bolting (flowering). This is why they need to be started indoors for spring planting, but you can start them outdoors (even trying direct sowing) for fall crops – they germinate in the heat and then slow growth as the temperatures drop.
A recent question posted to the Garden Professors blog Facebook group (a place where you can join and join in conversation of garden science) asked about the potential for compost added to seed starting media to cause failure in germination. It is a good question, and one that seems to have several different camps – from garden hero author folks swearing by it in their (non-peer reviewed) books, to fact sheets saying it isn’t a good idea.
I’ve always promoted that the best practice for seeds starting is using a sterile media to avoid such problems as damping off. Many of the problems I’ve heard associated with compost and seed starting are that improperly finished compost can introduce disease microorganisms to the media or cause phytotoxicity, it can make the mix too heavy and thus create anaerobic conditions that starve emerging seedlings of oxygen or cause decomposition, and there is the potential for residues of herbicides in composts using farm waste, manure, or lawn clippings as a feedstock. But does compost really pose a risk to seed starting? I decided to take a very quick spin through the literature to weigh the possibilities. Here are some of the potential issues and what a quick glance at the literature says.
Keeping the Germs out of Germination
Compost, even finished compost, has a high microbial activity. For the most part, the fungi and bacteria in compost are good guys that pose no threats to plants, they decomposers or neutral. But incorrectly managed compost can also harbor fungi such as Pythium and Rhizoctonia that cause damping off or even other diseases such as early and late blight if diseased plants were added to the compost and sufficient heat levels weren’t maintained. Composts that don’t reach 140°F and maintain that temperature for several days to kill off potential pathogens run the risk of introducing diseases into seedlings.
Many promote the use of compost and compost products for potential antagonistic effects on bad bacteria. We’ve discussed compost tea and the lack of conclusive evidence that it has any effect on reducing disease here many times before, and this article found that there is no significant effect of compost tea on damping off. Some other articles, such as this one, did find that commercially prepared composts added to media did suppress damping off. However, it is to be noted that these are commercially prepared composts, which have a strict temperature requirement and often require testing for pathogen and bacterial populations. Many home composters aren’t as proficient at maintaining temperatures suitable for pathogen elimination.
Even if the compost is pathogen free, introduction into a germination media could potentially increase the population of pathogens already present in the media (or that land on it from the air) by providing a source of food for bacterial and fungal growth. The sterile mixes aren’t just sterile from a microorganism perspective, they’re also sterile from a nutrient perspective as well to help inhibit potential pathogen growth. The seeds come with their own food, so it isn’t needed for initial germination – the seedlings should be moved to a more fertile mix once they’ve established their first set of true leaves.
You may be saying- “but we also direct sow seeds outdoors, where there’s lots of pathogens present in the soil.” While this may be the case, damping off is still a definite problem in direct sowing and the loss of investment in materials, lights, and time is generally much lower (and less painful) than in indoor seedling production. This is especially the case for large operations or for home gardeners who grow lots of stuff from seed.
This is the main issue that leads to the best practice recommendation to use a sterile seed-starting mix that doesn’t contain compost. If a mix contains compost, it should be from a commercial enterprise that follows best practices or pasteurized.
Maturity isn’t just for wines, cheeses, and people
Continuing to talk about proper composting, improperly finished compost that hasn’t properly matured (finished composting) can also lead to problems with seed germination. Unfinished compost can still have woody material included, which has a high C/N ratio and also contain/release phytotoxic compounds during the decomposition process. The presence of decomposition microorganisms in a high C/N ratio means that there is still decomposition happening, which requires nitrogen for the process. With absence of nitrogen in the media, the nitrogen from the seed or the seedling can be leeched out, effectively causing mortality after or even before germination. The tender seedling serves as a source of N for the decomposing fungi.
We’ve had this discussion before when it comes mulch. While mulch is perfectly fine on top of the soil, if it gets mixed into the soil there could be potential implications on N availability.
A germination bioassay is one tool commonly used to test for compost maturity. Quickly germinating (and inexpensive) seeds are germinated on the compost (or on filter paper soaked with an extract from the compost in some commercial operations). The rate of germination vs germination failure can give some insight into the maturity of the compost. This paper discusses the use of the technique for commercial sawdust compost used for potting media.
You can use a bioassay of your own to test for compost maturity (or herbicide persistence, discussed later) for applications in your garden. Sow an equal number of inexpensive, fast-germinating seeds like radish or lettuce sown on the compost with a control sown on moist paper towel in a bag. Compare the number of germinated seeds and thriving seedlings after several days to see if there is an issue with the compost.
Keeping Things Light
One other quality required for seed starting media is a good level of porosity (pore spaces) for the media to hold air. Air (oxygen) is important as it is needed by the roots for respiration. If the media is too heavy or holds too much water you run the risk of hypoxia, or lack of oxygen, in the roots. This can result in root die off and subsequent seedling failure. Most seed starting media are composed of very light materials such as peat moss, coir, vermiculite, or perlite for this very reason. Compost, by nature, is a more dense material with less porosity and has a higher water holding capacity. Therefore incorporation of too much compost can create the potential risk of compaction or excessive water holding in the mix.
When Persistence Doesn’t Pay Off
Most herbicides break down during the composting process through a variety of physical and biological interactions. However there have been reports of some herbicides that are persistent after the composting process, resulting in a residue that could damage plants grown using the compost (see this paper for some examples). Many of the reports show the damage manifesting in mostly large applications of compost to gardens. However, the more fragile nature of germinating seeds and young seedlings make them especially susceptible to herbicide residue damage. For further discussion (and examples of bioassays used to detect herbicide residues), check out this paper.
So the potential for pathogens, risk of improperly matured compost, effect on porosity, and potential for herbicide persistence present some significant risks to germination if they are incorporated into seed starting media. These are the risks that cause many sources to promote using sterile seeds starting media, and I think the advice is well founded. While some may not experience these possible issues, the potential is still there.
While most of those gardening tasks are coming to an end, in most parts of the US it’s time to think about planting a few things in the veggie garden to bring a flavorful bounty next year – garlic (and a few related alliums).
I often reference Halloween and vampires when I talk about garlic, not just because traditional lore says that garlic repels vampires, but because it is a good reminder of when to plant garlic in the garden. October is the prime time for adding the alluring allium to the garden. You can also remember that you plant garlic during the same period that you plant spring flowering bulbs.
Why do vampires hate garlic?
Yes. Vampires are fictional (unless someone finds some empirical evidence of their existence, since you can’t prove a negative 😉 ). These bloodsucking creatures of folklore may actually have a basis in fact that could explain their aversion to garlic. Way back when people didn’t have science to understand things, they often invented explanation for things that were supernatural. Sometimes these explanations may have actually had some truth to them.
In this case, the symptoms of vampiricism could have evolved from the symptoms of porphyria – a set of rare disorders of hemoglobin (there’s the connection between vampires and blood). Symptoms of porphyria include shrunken gums (that could make teeth look like long fangs), painful sensitivity to sunlight, and….and averse reaction to garlic. The reaction comes from the effect of garlic on the blood – it can stimulate red blood cell turn over and increase blood flow, both of which can exacerbate symptoms of porphyria and cause acute, painful attacks. There’s also an allegorical connection – vampirism was considered a disease (or represented the spread of disease in some literary cases) that was spread by a causal agent and garlic was seen as a curative for disease (it does have some antibacterial properties). Note: other possible symptoms of porphyria can be excessive hair growth in random areas of the body, which gives it a connection to lore around lycanthropy.
On to the gardening
Now that we’ve covered some trivial, albeit interesting, info lets get on with the gardening!
While many people are accustomed to the single variety available in grocery stores, there are several different types of garlic that all have different flavor characteristics. These types can be classed in two categories; hardneck garlic has a hardened central stem when it dries, and softneck garlics remain soft and pliable. Softneck varieties are the ones that lend themselves to being braided into those hanging garlic braids. Softneck varieties are also longer-storing than hardneck varieties.
It can be tough to find garlic in local garden centers to plant. Those that do carry garlic, often carry it at the wrong time of year for planting when it is shipped in on the spring garden displays. If you don’t have friends to share their garlic with you, or a local farmer to buy some from, you are going to have to go the mail order (or online order) route.
Once you have your garlic bulbs, split them up into cloves, being sure that you have a piece of the basal plate (the part that holds them all together) on the clove. This one clove will turn into a whole bulb over the growing season.
Plant the cloves tip up about 4 to 6 inches apart and about 2 inches deep in loose, organic soil. Mulch after planting with about one inch of straw or shredded newspaper.
Garlic is a relatively heavy feeder, so it would benefit from a good balanced fertilizer treatment with nitrogen after it is established. You can also plant them in the garden where you grew beans over the summer – the bacteria that colonized bean roots adds nitrogen to the soil.
After that, just be patient. It may pop up before winter if the weather is mild, but don’t worry – it can survive even if a freeze kills the growth back to the ground. Garlic requires little maintenance, and only requires water if the weather turns very dry. Harvest it once the leaves start to die in mid-summer (around July, unless it is an early-maturing variety). Be sure to save some to plant next year and store the rest for use in the kitchen.
Aside from garlic, there are some other odoriferous onion relatives you can plant this time of year like shallots and perennial onions in the vegetable garden or edible landscape.
Shallots have a mild onion flavor and are great because they form cloves like garlic (meaning you don’t have to cut up a whole bulb if you just need a little bit) and store well. The beauty of shallots is that they can also be planted in really early spring — they are a multi-seasonal crop. You can also start them from seeds in the spring.
Shallots are technically perennials, as they will grow over many years if left undisturbed. However, to harvest them, you have to dig them up so they are usually grown as annuals. Once you dig them up, use the larger bulbs for cooking and save the smaller ones for replanting.
Multiplier onions, sometimes called “potato onions” are another fall-planted perennial. These plants produce clusters of bulbs (hence the name “multiplier”) that are harvested in the early summer for bulb onions.
One of the benefits of these and other perennial onions is that you can harvest the green blades of the plant for use as green onions or scallions throughout most of the winter and spring.
Egyptian walking onions are another perennial that can be harvested either for its bulb or as a green onion. The name comes from the bulbils that form at the top of the flower stalk. When they mature, they get heavy enough for the stalk to collapse and fall over, creating a new bunch of onions away from the mother plant. You can allow them to do this to fill in an area, though most people limit it by harvesting the bulbils before they fall.
There are also perennial leeks that have a flavor similar to leeks and can be harvested as green leeks through the winter or dug up as small, tender leeks in the spring.
If you love growing perennial vegetables that add flavor to just about any dish, give these tasty plants a try. They’re really simple to grow and can keep your garden and your kitchen full of fun and flavors for years to come.
A quick primer on types of garlic
Purple Stripe — bulbs have purple on the outside. Some of the tastier garlics that become deliciously sweet when roasted.
Porcelain — popular gourmet variety. Usually has a more robust and spicy flavor. Bulbs are typically large and have large cloves.
Rocambole — Rich, complex flavors popular with chefs. Their scapes (edible blooms) form a double loop. They do not do well where winters are warm.
Asiatic/Turban — Do not store for long periods. Mature earlier in the season (late spring as opposed to summer) than other types. Flavors are usually strong and hot.
Creole — Attractive red color. Performs well where winters are warmer. The flavor is similar to (though milder than) Asiatic/Turban Varieties.
Artichoke — the grocery store garlic (California White) is an artichoke garlic, though other varieties have more complex flavors. Bulbs tend to have multiple layers of cloves.
Silverskin — often the last in the season to mature, these are the longest-storing garlics.
This is a common “garlic” planted by many gardeners because it has large, easy to use bulbs with a garlicky flavor. Though it is technically not a garlic species – it is a type of perennial leek.
Not really a botanically-correct statement, but you know what I mean. John Porter’s previous blog post did a great job of explaining cucurbit reproduction (loved the Pucchini). Though I was surprised to learn “not getting any fruit” is actually a problem. Can’t say I’ve had an issue with that, ever. We have a really vibrant bee population and they’ve been super busy.
I love growing squash of all sorts, despite not being a terribly gifted vegetable garder. Past Garden Professors posts have addressed this issue. One might ask, why on earth would a two-person household need a 60-foot-long row of zucchini? Because we can! Though if I recall, I intended to go back and thin the row. Whoops.
The zucchini hedge. And those aren’t weeds, they’re *biodiversity*.
By late summer, we usually end up with gummy stem blight, powder mildew or squash stem borer No sign yet, though any of these goodies could show up next week. The plants are all healthy and ridiculously enormous. It’s been very warm and dry, but we have a nice drip irrigation system in place.
So guess what happened when we got too busy to check on them for three days? Many more were still on the plants when I snapped this pic. I’ve worked zucchini in some form into every meal except breakfast. Joel’s still being a good sport. Next step is anonymous *gift* bags to folks at the office. Though I think I’m getting a reputation.
Normal-sized zucchini at top of photo for reference. Aargh.
Not all zucchini taste alike, as true fans know. The pale hybrid Bossa Nova, right, has very creamy and tender flesh with seeds that are really only noticeable when it gets, er, hefty. Bossa Nova is a recent All-America Selection and perfect for use with those spiralizer thingies. The ribbed/striped variety is Costata Romensco – an heirloom variety with really wonderful flavor. Humongous plants though, probably not the best choice for square foot gardening fans. Tigress is the white-flecked green selection, allegedly more disease resistant than most. Bright and sunny Gold Rush, an old-school AAS selection, adds some color and is a bit sturdier/keeps longer than yellow summer squash.
I won’t be trying to save seeds – as John noted, can be very tricky/futile when there are other cucurbits about. Plus it’s too much fun to pick out next year’s selections from the winter seed catalogs, when the prospect of bountiful zucchini stacked like firewood actually sounds appealing.
One of the things I miss (and sometimes don’t miss) after my move from West Virginia to Nebraska is writing my weekly garden column for the Charleston Gazette-Mail newspaper. It was a great way to always keep thinking about new things to talk about and a great way to connect with the public.
After I left, the newspaper replaced me with a team of 4-5 local gardeners who would take turns writing about their different gardening insights and experiences. Some have been really good, like the ones who were my former Master Gardener volunteers. However, sometimes I find the bad information and attitude of one of the writers off-putting and even angering.
Take for example this missive which equates sustainable agriculture (a term which is pretty well defined as a balance of environmental stewardship, profit, and quality of life) solely to permaculture and biodiversity while espousing an elitist attitude about “no pesticides, no fossil fuels, no factory farms, growing all you need locally and enhancing the land’s fertility while you’re at it.” He got all this from an old photo of dirt poor farmers who were apparently practicing “permaculture” – which I’m sure was foremost on their minds while they were trying not to starve to death. The fact is that our food system (and the food that today’s low income families) depends on comes from a mix of small and large farms. And most of those “factory farms” are actually family owned, and not everyone can afford to grow their own food or pay the premium for organic food (which still has been treated with pesticides and is in no way better or healthier than those conventionally grown).
Now, I know I no longer have a dog in that fight, but when I see bad information, especially when it is aimed toward an audience that I care deeply about I just have to correct it. So two weeks ago when I saw his latest gem of an article berating a woman (and basically anyone) for using lumber (and those who work as big box store shills to promote them) to build raised bed gardens and should instead till up large portions of their yard for the garden I was aghast. Putting aside the horrible advice to till up the garden (which we’ll talk about in a minute) or the outdated recommendation of double digging (proven to have no benefit), that advice is just full of elitist assumptions toward both the gardener and toward the technique. It is especially ridiculous and ill-informed to suggest that tilling up a garden and destroying the soil structure is much better ecologically speaking that using a raised bed (and we’ll talk about why in a little bit).
Don’t want to do a raised bed? Fine, it isn’t for everyone. But that doesn’t mean you should go out and till up a large patch of land that will degrade the soil, lead to erosion and runoff, and reduce production. It does not do anything to improve drainage nor aeration.
So let’s do a breakdown of why I find this article, its assumptions, and bad science so distasteful:
Bad Assumptions (and you know what they say about assuming)
The gardener didn’t have a reason for a raised bed other than she had been told that’s the way you do it.
This assumption fails to take into account the many different reasons why a gardener may prefer to use a raised bed. Does she or a family member have mobility limitations where a raised bed would provide access to be able to garden? Or does she have space limitations for a large garden patch? Would a raised bed make it easier for her to manage and maintain the garden? Making a blanket pronouncement against the technique fails to use empathy to see if it actually would make gardening more accessible or successful for the gardener. Is she wanting a raised bed because the soil in the ground at her house is too poor or contaminated? West Virginia is notorious for having heavy clay, rocky soil that is pretty poor for growing most crops. It can take years of amending to get it even halfway acceptable for gardening. Or perhaps she lives on a lot that had some sort of soil contamination in the past and she’s using raised beds to avoid contact with the contaminated soil.
Raised beds also have some production advantages – the soil heats up faster in the spring, allowing for earlier planting. A well-built soil also allows for improved drainage in areas with heavy soil or excess moisture.
The gardener has access to equipment to till up a garden space, have the physical strength and endurance to hand dig it, or is she able to afford to pay someone to do it for her?
Raised beds can often be easier for gardeners to build and maintain, often not needing special equipment or heavy labor. If the gardener isn’t supposed to benefit from these efficiencies, how will she go about tilling up the soil for her new garden. Does she or a friend/neighbor have a rototiller or tractor she can use? Is she physically capable of the often back-breaking work of turning the soil by hand? Or does she have money to pay someone to do it for her? So these “cheaper and easier” methods he describes could actually end up costing more and being harder than building a raised bed.
The raised bed has to be built out of lumber, which apparently only comes from the Pacific Northwest and is a horrible thing to buy. First off, raised beds can be built out of a number of materials. The list usually starts with lumber. Some people tell you to use cedar (which does primarily come from the PNW), since it is more resistant to decay, but plain pine that’s treated with a protective oil or even pressure treated is fine (it used to be not OK back before the turn of the century when it was treated with arsenic, but most experts now say it is OK since it is treated with copper). The dig against the PNW lumber industry is as confusing as it is insulting, since there’s lots of lumber produced on the east coast, and even a thriving timber industry right in West Virginia. Most lumber these days is harvested from tree farms specifically planted for the purpose or by selective timbering that helps manage forest land for tree health and sustainability.
The list can go on to include landscaping stone, concrete blocks, found materials like tree branches, and on and on. These days, you can even buy simple kits you can put together without tools and with minimal effort that are made of high-grade plastic or composite lumber. They’re getting cheaper every year, and can be especially affordable if you find a good sale or coupon.
Heck, a raised bed doesn’t even require the use of a frame at all….just a mound of well amended soil in a bed shape will do. No need to disturb the soil underneath, just get some good topsoil/garden soil in bulk or bags from your favorite garden center, mix it with a little good compost, and layer at least 6 inches on top of the soil. Use a heavy mulch on top if you are afraid of weeds coming up through the new soil.
The soil she’d buy is trucked in from Canada.
I’m guessing this has some sort of assumption that the soil a gardener should be putting a raised bed is like a potting mix composed primarily of peat moss. While many gardeners are trying to decrease the use of peat moss, which is a non-renewable resource harvested from Canadian peat bogs, the recommended soil for a raised bed is not potting mix or one that even contains a large amount of organic material. The recommended composition of raised bed soil is largely good quality top soil, which is usually sourced locally, mixed with a bit of compost which could be from home compost, a local municipal composting facility or producer, or from a bagged commercial product that is likely from a company that diverts municipal, agricultural, and food wastes into their product.
Bad Advice based on Bad Science (or lack thereof)
Tilling or disturbing the soil is a common and acceptable way to prepare a garden.
More and more evidence is emerging that tilling or disturbing the soil is actually one of the worst things you can do in terms of both production and environmental impact in agricultural production. First, tilling disturbs and in some cases destroys the soil structure. Destroying the soil structure allows for increased erosion, especially when the bare soil is washed away during heavy rains or blown away in heavy winds. Excess tillage and wind is what actually led to the dust bowl, which actually led to the early promotion of conservation tillage practices through government programs like Conservation Districts (and also gave us some great literature, thanks to John Steinbeck). Aside from the soil particles that erode, having open, tilled soil leads to nutrient runoff that contribute to water pollution.
One other structure negative is the production of a hardpan or compressed layer of soil that occurs just below the tilled area. This results from the tines of a tiller or cultivator pressing down on the soil at the bottom of where it tills and can drastically reduce the permeation of water and gasses through the soil.
The aggregates in the structure of un-disturbed soil provide myriad benefits to soil health, especially in providing the capacity for the growth of good microorganisms. Studies have shown that the population of soil microbes is drastically higher in agricultural soils that haven’t been tilled. Therefore, tillage reduces soil biodiversity.
One of the reasons for increased soils microbes in no-till soil is an increase in soil organic matter. No-till allows for some crop (roots, etc) to remain in the ground and break down. Tillage also incorporates more air into the soil, which does the same thing that turning a compost pile does – it allows the decomposition microbes to work faster in breaking down organic matter. This increased activity then decreases the amount of organic matter. So tilling the soil actually reduces organic matter. The structure and organic matter also allows no-till soil to have a higher Cation Exchange Capacity, or ability to hold nutrients.
When the carbon in the organic matter in the soil is rapidly depleted after tillage, it doesn’t just disappear. The product of the respiration from all those bacteria and fungi is the same as it is for all living creatures – carbon dioxide. The organic matter held in the soil therefore provides a great service (we call this an ecosystem service) in that it sequesters carbon from the environment. This can help mitigate climate change and even effect global food security.
Double digging does a garden good.
Look through many-a garden book and it will tell you to start a garden bed by double digging, which is a term used to describe a back breaking procedure where you remove the top layer of soil, then disturb a layer beneath it and mix up the layers. While it may not be as drastic as running a tiller or tractor through the soil, it still destroys the structure with the same negative outcomes as above. Additionally, while many gardeners swear by it, there is evidence that the only benefit to come from it is to prove to yourself and others that you can do hard work. It has no benefit for the garden and usually negative effects on the soul, psyche, and back of the gardener.
Large tilled up gardens are easier to maintain. One of the benefits of gardening in a bed, raised or otherwise, is that the close spacing allows you to grow more stuff in a smaller area. By reducing the area under production, you also reduce the labor and the inputs (compost, fertilizer, etc) that are used. Using the old in-ground tilled up garden method where you grow in rows means that you have more open space to maintain and will be using inputs on a larger area that really won’t result in more production (it is really wasted space and inputs).
So, how do you start a garden if you don’t want to build a raised bed and know that you shouldn’t disturb the soil?
So you realize that tilling up the soil is really bad from both an ecological and production standpoint, but you don’t want to build a raised bed structure? That’s perfectly fine. Gardening in a bed, raised or not, is a great, low-impact gardening practice.
To get started, you don’t have to disturb the soil at all. Simply adding a thick layer of compost and topsoil on top of the soil in the general dimensions of the bed is a good way to start a bed. No need to till or disturb. And over time, the organic matter will eventually work its way down into the soil. If you have really heavy (clay) soil, you’ll probably want to start with a fairly deep (at least 6 to 8 inches) layer of soil/compost.
Just cover with your favorite mulch to keep it in place and reduce weeds (I prefer straw and shredded newspaper, but you can use woodchips as long as you don’t let them mix in with the soil – something I never can do in a vegetable garden where I’m planting and removing things on a regular basis). Keep in mind that a good width for a vegetable bed is about four feet and you want a walkway of at least two feet between them. This allows you to not walk on the good soil, which can cause compaction.
If the spot where you want to put your bed is weedy, use your favorite method to remove weeds before laying down the layer of compost/soil. This could be through herbicide usage (keeping in mind most have a waiting period to plant, though some are very short) or mulch. If you are planning ahead (say at least a year), our Garden Professors head horticulturalist suggests a layer of woodchip mulch 8-12 inches deep that can turn a lawn patch into a garden patch. They reduce the weeds and build the soil as the break down.
It’s been awhile since I wrote about, or recommended a blog I like which I often use as a source of something to share to The Garden Professors Facebook Page, so I thought I’d revisit the topic this month.
Add a friend, chef Michelle Fuerst, to provide recipes and there you have it.
Our goal is three-fold: to share the fascinating biology of our food plants, to teach biology using edible, familiar examples, and to suggest delicious ways to bring the plants and their stories to your table. To judge by the questions we are often asked at dinner parties (“What is an artichoke?” “Why is okra slimy?”), some curious eaters genuinely want to know which plant part they are eating and how its identity affects the characteristics of the food.
Plants and food? Tell me more! Well, espousing the view that ‘a person can learn a lot about plants through the everyday acts of slicing and eating them’, The Botanist in the Kitchen ‘is devoted to exploring food plants in all their beautiful detail as plants – as living organisms with their own evolutionary history and ecological interactions’.
I first learned about the blog back in 2015 from an article in Business Insider, linking to their post on the various foods we grow, that were bred from one species of plant …
Six vegetables you can find in any grocery store and which most people eat on a regular basis are actually all from this one plant. Over the last few thousand years, farmers have bred Brassica Oleracea into six “cultivars” that eventually became many of the vegetables we eat …
Some species have undergone the domestication process multiple times, and with some of these species, each domestication effort has focused on amplifying different structures of the plant, producing a cornucopia of extraordinarily different vegetables or fruits from the same wild progenitor. Such is the case with Brassica oleracea. The wild plant is a weedy little herb that prefers to grow on limestone outcroppings all around the coastal Mediterranean region.
So if you enjoy learning about plants we eat, and trying various recipes with them, be sure to follow the Botanist in the Kitchen via email.
Previous posts here on the other blogs I’ve recommended: