Container Soil vs. Garden Soil

Potting Soil ZHG901

Potting Soil ZHG901We often talk about cultivating organic soil that is rich in microbial action, and full of organisms. Soil in your garden combines naturally occurring minerals with the various organic and mineral amendments you add. As the organic matter breaks down, it feeds layer after layer of soil biology — moulds, fungi, arthropods, earthworms, and so on. Right down to the microbial layer of bacteria and protozoa.

The richer the ecosystem, it seems, the more fertile your soil will be. Soil biodiversity also protects your soil, and acts as a kind of cushion against atmospheric stresses like drought or frost. The more lively your soil ecosystem, the better prepared it will be to bounce back from periods of stress.

It may be that this richly biodiverse soil will work well in some container growing situations. Particularly in larger containers like half barrels or raised beds, an ecosystem within the soil may be able to thrive and produce the same kind of natural fertility.

It raises the question then: Container soil vs. garden soil. In some situations, the benefits of keeping things sterile outweigh the benefits of biodiversity. Certainly, if you are planning to grow microgreens on a kitchen counter, in a warm ambient temperature, the introduction of mould and fungi spores are not desirable. Likewise, insects and earthworms are not ideal guests in an indoor setting.

It is difficult to manage a diverse ecosystem in an unnatural environment. I think the best approach is to make the most of what you can if your system does not allow for biodiversity. In this way of thinking, cleanliness is crucial. I recommend using sterilized seed starting mix for indoor sowing and microgreens. For larger projects like larger container gardening, bagged potting soil is probably the safest bet. As this soil is produced, it is heated and cooked to kill off seeds and microbes. What it lacks in biology, it makes up for in structure, drainage, and dependability.

In an indoor setting, or even in a patio container garden, I recommend getting rid of all spent soil by composting it or otherwise allowing it to break down outdoors. After a season of growing, most of its nutrients will be depleted. Any roots or debris from the previous season will activate the biological process, and potentially become home to mould, etc… It would be possible, in theory, for a very frugal container grower to sterilize spent soil, and amend it to the point that it could be reused. To do really large projects like growing microgreens for restaurants, this may be necessary. I prefer the simplicity of using fresh bagged soil, though.

Think of indoor growing as the artificial stage. Employ inert growing media and artificial light as needed. It’s when plant crops are grown out in the garden where biodiversity becomes the key to organic success.

Green Manure Cover Crops

Buckwheat as a Companion Plant

“Green manure” is the name given to cover crops that are planted for the purpose of adding nutrients and organic matter to the soil. These plants can be as effective as animal manure in producing humus, thereby increasing soil fertility and structure. Cover crops are inexpensive to plant, and serve multiple purposes. Best of all, they can be put to work during times of the year when growing food crops is not feasible.

A central concept of organic gardening is the notion of feeding the soil. We literally add organic matter to the soil to provide food for the organisms that live in the soil. They break down organic matter and minerals (and other elements) into forms that our crops are able to take up as nutrients. We want them to be able to do their work efficiently and to the best effect.

Aside from adding organic matter to the soil, cover crops have many other purposes:

They reduce soil loss from water erosion.

They maintain soil surface infiltration, so it does not compact.

Cover crops improve soil tilth (structure).

They scavenge nutrients that might otherwise leach from the field.

They feed and provide shelter for birds, wildlife, and beneficial insects.

They fix nitrogen in the soil.

This hardy annual grows so fast it can reach 1m (3’) tall in only three weeks. Then it blooms with white flowers that attract pollinating insects and beneficial hoverflies. Buckwheat grows so densely that it can be used to smother out competing weed species. Within ten days of blooming (or at any time before) it can be cut and tilled under to improve tilth and add organic matter. Buckwheat is a succulent, brittle plant that can break down completely into the soil in a matter of days. When breaking ground for a new garden, growing two consecutive crops of buckwheat and digging them in will provide ample organic matter to stimulate the soil biology.

Grasses & Grains
Oats, barley, wheat, and rye are all cereal grasses that produce a dense, fibrous root mass and a great deal of carbon-heavy biomass above ground. They are particularly well suited to protecting soil over winter, and some varieties are hardier than others. Even if they die back under frost, their roots will remain intact to prevent erosion. These plants also tie up quite a lot of soil nitrogen, which is then incorporated back into the soil as they break down.

Of all the nutrients needed to grow food crops, nitrogen is one of the hardest to maintain in soil. The Earth’s atmosphere is made up of nearly 80% nitrogen, but the element is not found in any parent rock, so all the nitrogen made available to growing plants comes, one way or another, from the air. Plants can’t make use of atmospheric nitrogen (N2), but they can absorb it from soil in the forms of nitrate (NO3) or ammonium (NH4). For the organic grower, the problem of getting nitrogen into the soil is solved through the use of legumes—members of the pea family, Fabaceae.

These plants have co-evolved with certain types of bacteria known as Rhizobia to form a symbiotic relationship that benefits both the bacteria and the host plant (and, happily, the organic grower). The roots of all legumes have tiny bumps called nodules that contain colonies of Rhizobia. The Rhizobia convert atmospheric nitrogen into ammonium, which benefits the host plant. In return, the plant supplies the Rhizobia with carbohydrates, proteins, and oxygen.

It is Rhizobia, by the way, that we introduce into the soil in large numbers when we use seed inoculant on legume crops. While some Rhizobia may already be present in the soil, using seed inoculant will kick-start that nitrogen-fixing process.

So instead of spreading chemical fertilizers, the gardener or farmer can simply plant nitrogen-fixing plants as part of their regular crop rotation. All that stored nitrogen in the soil will result in strong growth in any crop that follows. It makes particular sense in farming systems where fields might be vast—why not take advantage of a naturally occurring phenomenon, and let the plants and their bacteria do most of the work?

While there are nearly 20,000 species of plants in the family Fabaceae, there are a handful of these that work particularly well in organic farming systems. They have been selected ease of growth, hardiness, and the ease with which they can be turned under.

Crimson clover
This hardy annual can be planted any time between late March to early October, and will survive winter freezes down to around -23°C (-10°F). For overwinter growing, sow in September through October. Crimson clover does best in well-drained soil with a fairly neutral pH, and wants to be sown fairly thickly. Whenever you choose to sow crimson clover, it will flower in April, and that’s the time to till it under or pull it out. As it sets seed, the stems become fibrous and tougher to break down. This plant is particularly succulent and is easily tilled or hoed under. You can remove the tops to the compost, or simply turn the whole plants under. They will be broken down in about ten days, and the soil will be ready for planting nitrogen-loving crops.

White Dutch clover
White-flowering Dutch clover is a perennial that does best from spring or fall sowing, and it will overwinter even in Zone 4. It spreads by underground runners that call for more thorough tillage in the spring. Allow two weeks for this clover to break down in the soil.

Fava beans
Small seeded fava produces a taller plant than the broad beans you might plant for eating, so that increased biomass produces abundant green manure. Plants stay brittle until they begin to set seed, and can easily be scythed down or ploughed under even when they are four to five feet tall. You can cut the tops down to ground level and add them to your compost, and then till in the root stubble. Fava beans can be started as early as the end of January, or as late as early November. Plants grow slowly, and are hardy down to Zone 7.

Using Cover Crops

Cover crops can be planted to improve just about any kind of soil and render it more fertile. The trick is to choose the right plant for the job. Remember that the different cover crops can be mixed, as well. Barley and white clover can be inter-planted in the fall and grown all winter to produce a massive amount of organic matter and fixed nitrogen for crops the following spring.

Like all other crops, it’s useful to think of cover crops in terms of space as well as time. You need to calculate how much seed you will need for a given area, and how deeply they need to be planted. And you also need to think about the right time to plant, the right time to dig the crop under, and the amount of time it will take to break down. The charts below will help with your calculations.

The Poop on Manure

The Poop on Manture

What is manure?
Broadly speaking, manure is organic matter. Animal manure is the feces of animals—primarily of livestock like horses, cows, and chickens. It may be “pure,” but it often includes bedding or litter materials like straw or sawdust, in which case it will also contain animal urine. Facts about manure. Depending on the source, manure is very high in organic matter as well as nutrients essential to plant growth. As animals digest the plants and other food they eat, they are broken down by anaerobic bacterial action in their stomachs. Manure is, in some ways, like compost that has been broken down at high speed by the animals that have produced it.

Why use it?
Farmers and gardeners have been using manure for centuries to add organic matter to their soil. Over time, as organic matter breaks down in soil, it becomes depleted. The mineral soil that is left over becomes less able to support abundant microbial life, so by “manuring” such a field, the farmer is able to integrate organic matter into the soil and re-start or feed that microbial life. The microorganisms and invertebrates that live in soil break down minerals and organic matter into forms that are accessible to plants. So if you have a healthy soil biomass, you can grow healthy crops without the use of chemicals.

Animal manure is a bi-product of farming, and there’s quite a lot of it about. Cattle in the US alone produce an estimated two billion tons of manure each year. In some traditional farming systems, livestock are kept primarily because they produce manure. Depending on where you live, you may be able to find farms or horse stables that are anxious to give the stuff away because their animals produce so much of it. But as we shall see, not all manures are created equally.

Fresh vs. “Mature” – how to store it
Using manure that has been freshly dug from the barn, coop, or paddock poses problems. Depending on the kind, it may be very high in ammonia, or contain so much nitrogen that it will burn the roots and stems of any plant it comes in contact with. It might also be full of weed seeds. Fresh manure may also contain pathogens from the animal’s gut. Storing manure allows it to mature in the same way that compost does—bacterial action causes a buildup of heat that will, ideally, kill weed seeds and other pathogens.

If you order a delivery of manure and it smells upon arrival, it is unfinished, and needs to be stored (composted) before use.

Stored manure is often referred to as “rotted manure.” It has no unpleasant smell, and its texture has changed since it was produced. Rotted manure is a fantastic soil amendment. Ideally it will retain some of its natural nitrogen, but not to the extent that it causes burning or excessive foliar growth in your crops. In some farming systems manure is stored for a year in a pile with steep, compacted sides. This helps to retain some of its inherent nitrogen (as does covering the pile with tarps), because rain is prevented from leaching out the nitrogen. But some moisture is needed in the pile to encourage microbial action, so you don’t want it do dry out entirely. If it does, you’ll want to give it a good soaking before use.

Fresh manure can be spread over a growing area in the fall, and incorporated into the soil in the late winter prior to planting. By the time you are planting, it should have no unpleasant odour. Certified organic farmers are prohibited from spreading fresh manure for at least 90 days before harvesting crops intended for human consumption. For crops that come in direct contact with the soil, the minimum time period is 120 days. These regulations are useful to the home gardener, to indicate how seriously this is taken.

How to use it
Rotted manure can be spread on the surface of the soil or tilled into the soil. Many organic growers prefer a “no-dig” method in which manure and other soil amendments are added to the soil in layers, always on the surface. This encourages sub-soil microbes and creatures like earthworms to feed on the material at the surface, and drag it down into the sub-soil. Tilling works, too, but may be disruptive to sub-soil life. Because the texture of rotted manure is relatively fluffy, compared to soil minerals, most of it is going to remain near the surface, even when tilled.

The amount that you choose to incorporate should be relative to the area in question, and the existing fertility and structure of your soil. A farmer with depleted, dusty soil, for instance, might want to apply manure at a rate of 40 tons per acre. She might apply half that amount if the existing soil is thought to moderately fertile. In subsequent years, 10-20 tons applied every other year would maintain adequate fertility.

Remember that it is possible to over-apply organic matter of any kind. Soil wants to maintain an ideal balance (loam) of soil particles (sand, silt, and clay) with organic matter. And while there are a few types of hardy plants that will thrive in pure manure, it’s more useful to think of manure as organic matter—as a general soil amendment to promote microbial action.

Types of manure
Animals digest their food in different ways. And different animals eat different sorts of food, so it’s no surprise that the end product will vary from creature to creature. So after your manure’s “maturity,” it’s type is a critical consideration.

All birds have relatively high metabolisms and body temperatures. One of the best qualities of chicken manure is that few, if any, weed seeds can survive passing through the gut of a chicken. The manure of all poultry (turkeys, pigeons…) is a combination of feces and urine, and it’s extremely high in nitrogen. Fresh chicken manure is far too strong for direct application, so it should be fully composted. In small quantities, it makes a good additive to your compost pile, combining well with high carbon matter like lawn clippings and leaves. As a fertilizer, mature chicken manure has an NPK rating of 1/1.5/0.5.

This may be the most balanced of all manures for organic growing because of the nature of cows’ stomachs. Cows can digest the cellulose that makes up so much of the bulk of the plants they eat, so their manure breaks down very easily. It also tends to be moist, which helps in the composting stage, and it’s not strong in terms of nutrients. Composted steer manure typically has an NPK rating of 0.8/0.5/0.5.

Horse manure is abundantly available and well balanced. Horses digest their food less thoroughly than cows, so their manure is richer in organic matter. It is, however, more likely to contain viable weed seeds. Horse manure often contains bedding and straw soaked with nitrogen-rich urine, which is of particular value to growers. Expect an NPK rating of 0.5/0.3/0.4.

Pig manure should be composted to the point that it has little or no smell before use in the home garden. It is noxious as a fresh product. Be cautious of manure produced from intensive meat production facilities, as it may be high in copper. Organically farmed pig manure is an excellent amendment with an NPK averaging 0.6/0.4/0.3.

Sheep & Llama
These animals spend a great deal of time outdoors leaving their droppings in the field. But any that can be collected is very valuable as garden manure. Like cows, these animals digest their food well. Their potassium rich fertilizer has an NPK rating of 0.4/0.3/0.8.

Rabbit pellets are high in nitrogen and phosphorus. Some of the literature suggests that if the pellets are kept dry, they can be used fresh, simply scattered around plants like pelleted plant food. This should be done with some degree of caution, as the pellets can be soaked with ammonia-rich urine. In a food growing system, it’s probably safer to compost rabbit pellets before use. Its NPK rating is 2/1.4/0.6.

Mushroom manure
This product can be purchased in bags, or is sometimes available in bulk amounts. It is the residual waste of the mushroom growing industry, and is usually comprised of a mix of straw, horse manure, dried blood, chalk, and other ingredients that have been thoroughly composted. If you can find organic mushroom manure, it’s an outstanding soil amendment with an NPK of 0.7/0.3/0.3. Mushroom manure that is not specifically listed as organic may contain traces of pesticide residues used to control fungus gnats.

Green manure
Not all manure exits the gut of an animal, of course. Green manure is a general name for cover crops that are grown with the intent of tilling under. They may add carbon, or other nutrients to the soil, and improve structure and drainage. Legumes are planted to fix nitrogen in the soil through a symbiotic relationship with bacteria. The uses of green manure are broad enough to justify their own article.

Slurry & Tea
In some larger farm systems, fresh dairy cow manure (and other types) is collected in concrete basins, and mixed with water to form “slurry,” which is then machine spread on fields prior to tilling or planting. On a much smaller scale, compost and manure tea can be made for the home garden or small farm. This involves steeping organic matter in water, straining it, and using the resulting tea as a foliar or crop fertilizer. Because the decomposition of the organic matter is anaerobic, it can result in a seriously stinky final product. But it is cheap to produce, and very effective.

Try filling a bucket 1/3 full of aged manure (or ½ full of finished compost), and top it up with water and a tight fitting lid. Let this steep for about one week, and then strain the tea into another container. The tea should be diluted one part tea to two parts water before use.

While the thought of using human waste in food production may be offensively unpalatable to Western growers, it’s worth considering that such waste is far too valuable in some parts of the world to waste by simply polluting rivers. Human manure can, indeed, be composted and spread for crop production. Human urine is extremely high in nitrogen, and has its uses in the garden as well. If you are compelled to experiment with human manure, it’s probably worth doing some thorough research beforehand. Many websites and several books have been dedicated to the subject. The use of human manure is banned under organic certification for farms producing food for human consumption.

Problems with manure
Some organic food proponents are vehemently opposed to using animal manures of any kind. Scientific evidence appears to show that it is possible for some plants to accumulate antibiotics from soil amended with animal manures that contain these drugs.¹ It should be pointed out that manure might be available from organic farms where no antibiotics are used, or that keeping your own chickens organically is one way to address this concern.

Pathogens such as E. coli and salmonella can exist in manure, and have been known to cause outbreaks in human populations due to improper use. By composting manure, its interior temperature can be raised to 55-60°C (130-149°F) for two weeks or longer, thus killing these pathogens and rendering the manure safe to use. Properly composted manure is considered safe for use in organic farming systems, and by the regulatory bodies of the CFIA and USDA.

The other major issue is with the introduction of weed seeds, but as we’ve seen above, some manures are less likely than others to contain them. And if correctly composted, many of these seeds can be sterilized by achieving high temperatures through bacteriological action.

There will be some growers who simply can’t be sold on the concept of using manure to grow food, and fair enough. By using cover crops to create green manure, nearly all the benefits of using manure can be achieved—namely the introduction of nitrogen and organic matter into your soil to improve soil fertility and structure


Soil Temperature and Day Length

Soil Temperature and Day Length

The changing seasons, and the longer daylight hours in summer are a result of the angle of the Earth’s axis in relation to the sun. It’s easy to forget how these changes can affect the growth of plants, and in particular, vegetables. Soil temperature plays a very important role in the success or failure of the vegetable garden. Beet seeds, for instance, do not require particularly warm soil to germinate, and they will produce nice leafy tops if sown in early spring, but if the soil is too cold at planting time, they may not produce well-developed roots. By contrast, spinach planted when the soil is too warm may “bolt,” or pass to its flowering stage without producing any leaves.

Leafy vegetables like lettuce, spinach, mustards, arugula, sorrel, pac choi, and cress prefer growing in cooler soils, so we focus on them in spring and again in the fall and, with some protection, in winter. For this group of plants, warm soil represents a stress that signifies the end of the growing season. The plants urgently send up flower stalks and devote their remaining energy to setting seed. Because of this, their leaves tend to become tough, bitter, or unpalatable. When you see references to “bolt-resistance” in lettuce, it’s because the variety has been bred to resist this phenomenon longer into warm weather.

Aside from warming soil, other stresses can cause plants to bolt. Drought can trigger it, so consistent irrigation is important. Some plants (dill, for instance) may bolt when they are transplanted – the shock of root disturbance and cooler nighttime temperatures will sometimes produce very short plants with flowers but few leaves. To avoid this, dill growers usually direct sow their seeds in late spring.

Day length also plays an interesting role in the lives of some plants. The phenomenon known as “photoperiodism” dictates which plants bloom at different times of the year. Many plants use a protein in their tissues to detect changes in the number of hours of darkness in each 24-hour period. As nights grow shorter in late spring and early summer, the flowering process is triggered. Plants that fall into this category are called Long-day Plants, and include oats, clover, peas, barley, lettuce, turnips, and many others.

Short-day Plants have the flowering process triggered by the arrival of increasing hours of darkness, so they typically flower after the summer solstice. Plants in this category include strawberries, tobacco, chrysanthemums, rice, and others. Yet another category of Day-neutral Plants exists (including cucumbers and tomatoes) that bloom regardless of the day length. These plants tend to bloom once they reach a certain stage of maturity, and because of this, they simply don’t bolt.

Onions have the curious distinction of coming in both Long-day and Short-day varieties. Day length triggers bulb formation in onions. Long-day onions need a day length of 14-16 hours in order to trigger the bulbing process in summer, whereas Short-day varieties bulb up when the day length is 12-14 hours. This is an important consideration for growers, and relates to the latitude at which they are grown. Here in BC, and elsewhere in the northern half of North America, we grow Long-day onions. Down in Georgia, where masses of onions are farmed, they grow Short-day types. West Coast Seeds only offers Long-day (and occasionally day-neutral) onion varieties.

Soil Amendments

Soil Amendments

Anything that we add to soil to improve its texture, structure, fertility, porosity, or other qualities, is considered a soil amendment. The use of soil amendments is an ancient art, and the basic premise is that by employing them, pretty much any piece of land can be made fertile. The type of amendment to choose depends entirely on how the soil needs to be changed.

One of the first things to consider is the pH of the soil. If your soil is too acidic or too alkaline, plants will not be able to take up the nutrients that are present. Adding fertilizer or other amendments to soil with an extreme pH will not help – you have to address the pH issue first, and it’s a relatively simple process.

Soil Amendments

Agricultural lime is a pulverized rock powder made from chalk or limestone that is high in calcium. Dolomite lime comes from a different source and is also high in magnesium. Both of the elements have the effect of raising the pH (lowering the acidity) of soil. They work in essentially the same way as the antacid pill you might take for heartburn, by neutralizing acidity, but they have the added benefit of adding essential minerals to the soil. Both calcium and magnesium slow the process of soil becoming acidic again.

Various kinds of plants do better with different levels of soil acidity. We recommend adding lime to your garden every three years in this region, and following a three-year crop rotation method that takes advantage of the soil as it gradually becomes acidic again. In the first year, add your lime in late winter. Plant leafy vegetables like lettuce and spinach, as well as the various Brassicas (cabbage, broccoli, cauliflower, kohlrabi…) which all appreciate neutral soil and high levels of calcium. In the second year, the soil will begin to turn slightly acidic, so you would plant legumes like peas and beans, as well as onions and squash. By the third year, your soil will be on the acidic side, so you would plant varieties that thrive in acidic soil: tomatoes, peppers, eggplants, potatoes, and other root crops like turnips and carrots. At the end of this season, you would lime the soil once more.

Organic Matter
Adding organic matter to the soil is one of the fundamental principles of organic gardening. It feeds soil microbes, which in turn release nutrients into the soil, increasing fertility. Organic matter also adds body to soil, and can improve the soil’s ability to conserve moisture. Organic matter should be added to garden soil every year, prior to planting.

We like to add a layer of compost, well-rotted manure, leaf mulch, or even plain straw to the surface of the soil during times when the garden is not productive. This creates a lush habitat for beneficial soil organisms.

Glacial Rock Dust
Glacial Rock Dust is a naturally occurring powder of minerals pulverized by the movement of glaciers. It contains a broad spectrum of nutrients that improves soil structure, mineral imbalance, and moisture-retaining ability. It helps to neutralize soil acidity (although with less effectiveness than lime), and it increases bacterial action. You can add glacial rock dust at any time of the year – but do it on a still day, or when it’s raining, as the powder is very fine. You cannot over-apply glacial rock dust.

Alfalfa Meal
Alfalfa meal is a byproduct of the alfalfa growing industry, and contains such a broad spectrum of nutrients that it acts as a low intensity fertilizer. It’s a great thing to add to compost piles or directly into the garden soil, as it accelerates the breakdown of organic matter and fuels microbial activity.

Since ancient times, seaweed has been gathered from beaches around the world, and hauled inland to enrich garden soil. It breaks down easily and releases a lot of potassium, as well as a broad spectrum of micronutrients. It also contains growth-stimulating hormones that lead to vigorous growth and good resistance to pests and disease. Kelp can be added as a mulch in winter, or put directly into the compost pile. Be sure to leave any seaweed that you collect from the beach out in the rain for several days to rinse off excess salt. And use it sparingly – maybe once a year – to prevent a build up of sodium in the soil. Otherwise, you can try using one of the prepared kelp-based fertilizers on the market like Kelpman. This is a concentrated product that can be used throughout the year as a liquid or foliar fertilizer.

Manure and Farm Waste
Bedding from animal stalls and manure are excellent sources of Nitrogen and other nutrients, but it is essential to let them rot completely before adding them to your garden. Fresh animal manure can contain as much Nitrogen as chemical fertilizers, and can burn plants or stunt growth. If you have access to organic farm manure, try accumulating some in a pile in the corner of the garden this year, and incorporating it into your soil next year. Bagged manures are available from most garden centres, and come pre-rotted. Look for products with little or no odour. Mushroom manure is a byproduct of the mushroom growing industry and contains primarily chicken manure that has been completely decomposed.

This is silicate mineral containing 20% iron oxide, 7% potassium, and as many as thirty other elements. It has the unique ability to loosen hard soils as well as bind sandy soils. It’s a naturally occurring seashore deposit that regulates the release of nutrients in soil and assists in moisture retention. If you have clay soil, don’t add sand – add Greensand.

Follow the guidelines in the West Coast Seeds Gardening Guide for each variety. A fertilizer like the Complete Organic 4-4-4 will build stronger plants with better resistance to disease and stress, and with larger and more abundant fruits or roots. Most potting soils have enough nutrients that fertilizers are not necessary for seedlings until they are transplanted to the garden. Generally speaking, you want the fertilizer to go beneath each transplant, but not in direct contact with its roots. In a typical situation (transplanting a tomato plant, for example), you would dig a hole slightly deeper than the root ball of the seedling. This allows the fertilizer to be worked into the soil at the base of the hole, and then a little soil added to cover it up before the transplant is set in place. The roots of the transplant will eventually reach that rich layer of fertilizer, but on their own time. Even organic fertilizers may burn tender roots. Finally, avoid the temptation to over-fertilize. Soil can only be so nutritious, and being too generous with fertilizer is simply wasteful.

Soil Basics 101


In the cool, damp, and dark season from late fall to early spring, not a lot is growing outside. Even the plants you may have under cloche protection or in the greenhouse will be growing slowly, struggling to turn the low light levels into useful energy for vegetative growth. This is the right time of year to learn about soil science and think about how you can improve your garden soil before new seeds are sown or transplants go out in the spring.

There are four central issues that offer a better understanding of garden soil and how it can be improved: Soil structure, soil components, soil life, and soil pH. Gardeners (and farmers) will benefit from contemplating these four factors on their own and in harmony with one another.

Soil Structure
This refers to the ratio of particles that make up the soil itself, and they may be sand, silt, or clay. The size of these tiny particles dictates physical aspects of the soil like drainage, compaction, and porosity. Sand is made up of relatively large particles, even if it is as fine as table sugar or salt. Sand is essentially ground up rocks, and can be composed of a number of different minerals. Because sand particles are so large, the spaces between each are also large, so water tends to drain through it rather quickly. The large size of sand particles also means that they don’t move around that much within the soil structure.

Silt particles, like sand, are the result of mechanical grinding action, but they are much smaller than grains of sand. Think of finely milled flour in comparison to relatively coarse salt when comparing silt to sand. Silt is so fine in texture that it can wash through soils fairly easily. It’s a major contributor to soil’s ability to clump together or form aggregates.

Clay particles are flat and plate-like. Unlike sand and silt, clay is the result of chemical action, as minerals are worn down by water and acids in the soil. Clay particles can be 1,000 times smaller than sand particles, which is why pure clay has such a unique, plastic texture. It clumps together so well that clay soils can have very poor porosity and drainage.


So when soil experts discuss soil texture, it’s the range from sandy soil to clay soil that they’re talking about. The term ‘loam’ is used to describe the ideal range of soil texture, and is made up of 40% sand, 40% silt, and 20% clay. It clumps together and holds moisture well, and it breaks up easily when it’s dry, instead of becoming hard and packed. Good loam contains particles in such a variety of sizes that the spaces between them are also varied, and this is good for porosity.

Soil Components
The four components of soil play dramatically different roles to the health of the soil itself. Minerals (those sand, silt, and clay particles) make up about 45% of the overall mass of soil. Of this percentage, nearly 90% is composed of the elements silica, iron, oxygen, and aluminum. Minerals play a mainly physical role in soil health.

Water and air are both present in soil, and each account for around 25% of the soil’s mass. Water and air interact with the mineral components of soil in ways that affect drainage, aeration, compaction, and porosity. These are important factors when growing plants, as the roots of all plants need to penetrate soils easily, draw off mineral nutrients, absorb water, and exchange gases. Soil organisms, as we shall see, also depend on the varying amounts of water and air present in soil.

The remaining 5% of the mass of soil is made up of organic matter and humus. Gardeners define organic matter as any dead plant or animal matter that is added to the soil. It is typically made up of compost, animal manure, or crops that have been planted the previous season and then tilled under. Organic matter feeds soil organisms, and fuels the “life” of living, healthy soil. Once it has been broken down, and its nutrients consumed by plants and microorganisms, it becomes humus. Humus adds bulk to soil, and makes it that rich, dark colour – which in turn allows soil to absorb and retain more heat, which also makes the whole system work better.

Soil Life
The “life” of living soil mentioned above is key to the success of organic growing. Healthy soil should be, as one author titled his book on the subject, “teeming with microbes.” Some soil organisms are present in astonishing numbers, too. Frank Tozer examines this subject in detail in his great book, The Organic Gardener’s Handbook, and describes the presence of various soil microbes in terms of pounds per acre of healthy soil:

Protozoa – 100 to 200 lbs/acre

Actinomycetes – 800 to 1500 lbs/acre

Algae – 200 to 500 lbs/acre

Bacteria – 100 to 2000 lbs/acre

Fungi – 1500 to 2000 lbs/acre

Earthworms – Up to 900 lbs/acre

Even if you don’t care to imagine what 900 lbs of earthworms look like, they and their fellow organisms play a fundamental role in soil health. Each of these different types of soil life acts to break down the nutrients in organic matter into forms that are accessible to plants. Some, like bacteria, may play multiple roles, and act to fix atmospheric nitrogen in the soil. Others, like earthworms, actually play a physical role in soil health by turning the soil, just like we would with a fork. They come to the surface to feed, and drag all of those nutrients down into the soil substrate where they can be reached by the roots of plants, or converted in other ways by the different microbes that exist at various depths.

Supplying organic matter to the soil (literally feeding the life that lives in it) is the central pillar of organic gardening. Soil with a diverse and functioning life within it is inherently more nutritious to the plants that we grow. The process of growing plants is one of drawing nutrients out of the soil so that we can, in turn, enjoy them as food. So organic growers are in a constant rush to push more organic matter down into that soil.

Soil pH
This is the final consideration of soil health, and it has to do primarily with chemistry rather than biology. The abbreviation pH is shorthand for “potential Hydrogen.” As water enters soil through rain or irrigation, its molecules become part of a chemical soup. pH measures the ratio of positively charged Hydrogen ions to negatively charged hydroxyl ions. Some of the water molecules form solutions with minerals in the soil and create new compounds, and others bond with clay and humus, creating acidic compounds.

Without going to deeply into it, the end result of these chemical reactions is a fluctuation of acidity or alkalinity in the soil. Nearly all food plants prefer soil that is neutral – not too acidic, not too alkaline. The pH range is measured from 1 (extremely acidic like stomach acid) to 14 (extremely alkaline like lye). 7.0 is considered the happy medium of total neutrality, and distilled water will have a pH reading of 7.0. A number of products are available to the home gardener to help determine the pH of their garden soil.

If soil is too acidic or too alkaline, the nutrients present in the soil become less easily available to plants. At the same time, these extremes make other toxic elements in the soil more available. Soil that is routinely saturated with water, as ours is in South Coastal British Columbia throughout the winter, has a tendency to become acidic. Wet, acidic soil, also throws the soil life out of balance, and encourages some anaerobic bacteria, while discouraging other soil creatures. As a result, we must take regular action to neutralize the pH of our soil. See below for the second part of this article: Soil Amendments & How to Use Them.

Soil Block Recipe

Soil Block Recipe

Soil Blockers have been around for many years, but their popularity is spreading fast, largely by word of mouth. Using this Soil Block recipe and Soil blockers will eliminate the need for plastic seedling trays and insert flats, so they represent an ecologically sound alternative for people who find themselves starting masses of seeds.

Soil Block Recipe

A soil blocker creates individual cubes of lightly compressed soil. A single seed is planted in each block and grown into a seedling to the stage it is ready to transplant into the garden – or into a larger soil block. Because the sides of each soil block are exposed to the air, the roots of each seedling get plenty of oxygen. This makes the roots stronger and minimizes transplant shock when the block is eventually planted.

Like seeds themselves, soil blockers come in various sizes. A ¾ inch soil block may be an ample size if you’re starting some tiny seed like thyme or Lobelia, but if you’re starting pumpkin seeds, you might want to begin with 3 inch soil blocks.

Soil blocks are also designed to fit inside one another. A mini ¾-inch block can be potted on into a 2-inch block, and this can be inserted into a 4-inch block. So even if you’re sowing seeds that need a very early start (like peppers), you can move the seedlings from block to block without disturbing the roots.

In Eliot Coleman’s outstanding book, The New Organic Grower, he devised a soil block recipe so perfectly proportioned that it has become an industry standard. We paraphrase his recipe here with a nod of respect to this guru of organic growing:

Soil Block Recipe

Use a 10-quart bucket and standard kitchen measuring cups to mix the following ingredients:

3 buckets finely milled peat
½ cup lime (use agricultural lime if you can get it)
Add 2 buckets coarse sand or perlite and
3 cups base fertilizer (Gaia’s All Purpose 4-4-4 is a good choice)
Mix again and add
1 bucket garden soil or bagged topsoil
2 buckets screened compost
Mix all ingredients thoroughly

This recipe produces about 2 bushels of soil block mix.

Coleman explains:

“The lime is combined with the peat because that is the most acidic ingredient. Then the sand or perlite is added. The base fertilizer is mixed in next. By incorporating the dry supplemental ingredients with the peat in this manner, they will be distributed as uniformly as possible throughout the medium. Next add the soil and compost and mix thoroughly a final time.”

Making Soil Blocks

Use a large container with a flat bottom to mix and make soil blocks. For a small farm that is going to produce masses of soil blocks, a surplus bathtub works well.

Mix in enough water to create a very wet mud. It needs to be deeper than the depth of the soil blocker itself. Press the blocker into the mix, against the bottom of your mixing container, and give it a ¼ twist, lifting it at the same time.

Eject the soil blocks by gently and steadily pushing down on the plunger as you raise the blocker. Give the soil blocker a rinse in warm water before you press the next set of soil blocks. You can build trays to receive your soil blocks, or use Seedling Germination Trays – but be sure to poke drainage holes in the bottom so your soil blocks are never sitting in water.

The Micro 20 (HG700) produces 20 individual soil blocks measuring ¾ inch on each side. On the top of each block is a shallow dimple that will receive one seed. These soil blocks can be moved on into larger blocks by employing the ¾” Cubic Insert Pin (HG708A).

The Mini 4 creates four 2” soil blocks at a time. This blocker comes with seed pins that indent the tops to receive seeds. These are interchangeable with Dowel Pins (HG708C) for large seeds, and ¾” Cube Insert Pins (HG708A) to receive soil blocks from the Micro 20.

The Mini 5 produces five soil blocks that are 1 ½” per side. This soil blocker is usually used on its own, but its soil blocks can be potted on into the large 4” blocks from the Maxi 1 Blocker.

The Multi 12 is a stand-up model that forms twelve 2” soil blocks at a time. Its seed pins are interchangeable with the Dowel Pins (HG708C) or 3/4″ Cubic Insert Pins (HG708A), and its soil blocks fit snugly inside the 4” blocks from the Maxi 1 Blocker.

The Multi 20 is for big farm jobs, producing twenty 1 ½” soil blocks at a time.

The Maxi 1 creates a single, large, 4” soil block with a 2” cubic indentation at the top. The blocks put out by this behemoth are meant to receive other soil blocks (1 ½” or 2”), and not individual seeds by themselves.

Nitrogen fixers

Here’s a bit of geeky plant science for you. David Bradbeer at the Delta Farmland & Wildlife Trust sent me this great image of the roots of white clover. You can plainly see bumps along the roots that are called nodules. Over millions of years, the plant has evolved a symbiotic relationship with certain species of soil-dwelling bacteria called Rhizobia. This group of bacteria has the ability to take nitrogen from the atmosphere and “fix” it by metabolizing it into ammonium, which is a nitrogen compound that the plants can make use of. The plants benefit by using this extra nitrogen to compete with their neighbours by growing stronger and faster. Without the nodules along the plants’ roots, the bacteria could not exist, let alone function. It’s a win-win situation.

Clover is a member of the family Fabaceae (all are called Legumes), and many plants within this family share this quirky talent to host nitrogen-fixing Rhizobia. Some of the best known of these plants are soy, peanuts, beans, peas, lupins, sweet peas, chickpeas, licorice, carob, alfalfa, and vetch. Each plant has a relationship with its own species of Rhizobia, although there is some cross-over. When the plants are harvested or die back, the nitrogen (in ammonium form) is left in the soil, making it more fertile for the next crop that is planted. Nitrogen, after all, is the most difficult of the major plant nutrients to maintain in soil.

P1120554It makes sense, then, that organic farmers would grow a crop of nitrogen fixing plants and then till them under before planting a marketable crop. Tilling the plants under takes advantage of their organic matter as well as the nitrogen in their root nodules. In conventional farming, the grower might simply apply hundreds of pounds of ammonium nitrate to her field, simply spreading the raw chemical before planting. In organic farming, a simple cover crop of nitrogen-fixing legumes is planted and grown for around three months before the main crop goes in.

Seed inoculants are simply a powdery form of Rhizobia. Seeds are dampened and then coated with this powder prior to planting. This introduces an abundant population of nitrogen-fixing Rhizobia into the soil at the time of planting, and kick-starts the whole process. If legume seeds are not inoculated, they will still develop root nodules and become hosts to Rhizobia, but more slowly.

Taking advantage of nitrogen-fixing cover crops seems very similar, in my view, to planting flowers that attract beneficial insects like predatory wasps. The grower is able to encourage natural processes to take place that will benefit the crop plants. No chemicals are used. Nothing unnatural takes place. The whole system is sustainable and environmentally sound.