Enhancing Your Soil

The short version of how to improve your soil is easy: Add Compost.

If you want to learn more, keep reading. Otherwise, feel free to go out to your garden and just add compost. (For tips about how to make compost, go to Compost. For comments on purchasing it, go to Garden Supplies.)

One of the most important thing to realize about soil is that it is a community. We can’t see most of the things that live in soil, but even a teaspoon of healthy soil is full of a multitude of life-forms. If we want healthy plants, we need to have healthy soil, and that means fostering a healthy soil community.

Healthy soil contains:

Inorganic material = ground-up rock

➢ Clay – small particles, often shaped like plates, hold water in place

➢ Sand – large particles, irregularly shaped, let lots of water through

➢ Silt – mid-size particles, irregularly shaped, water flows at a good speed

Humus = organic matter that is no longer living, holds onto water like a sponge and gradually releases water and nutrients

Bacteria: Includes nitrogen-fixing bacteria

Fungi: Includes mycorrhizal fungi

Animals: Includes ants, earthworms, etc.

Plants: Includes roots and seeds

Air: Includes oxygen (needed by roots) and carbon dioxide

Water: Necessary, but too much water drives out air

Healthy soil has layers:

1. Duff – the stuff that falls on top of the soil and hasn’t yet decayed (if people put it there, we call it mulch)

2. Surface growth layer – the top 2-8 inches or less, where nutrient, oxygen, and water levels are relatively high and plant roots grow densely; one of your goals as a gardener is to make this surface layer deep and fruitful, but there’s only so far air and water will penetrate

3. Deeper growth layer – the next 2 feet or more, where deep-growing plant roots pull up nutrients and stabilize the plant (even lettuce roots will grow 3 feet down if they can!)

4. Subsoil and/or bedrock – the hard-packed soil or rock underneath the fertile layers, in which little life exists

Healthy soil is in flux:

Ants and earthworms create open spaces for air and water to flow through. They also move nutrients around and make them biologically available. Roots similarly create passages through the soil when they first grow and then die back in the winter. Bacteria and fungi create useful relationships with plant roots and help them get the nutrients they need from the soil and air.

How to improve your soil …

Compost is the best thing to add to your garden, since it improves both soil texture and nutrient density. Compost is largely humus, which absorbs water readily and then releases it as the soil dries, so your plants will be a lot less water-stressed if your soil has plenty of compost. Compost also generally contains all the nutrients your plants will need.

Sometimes, however, you don’t have enough compost, or a soil test indicates your garden has special needs. In that case, you might want to consider things other than compost.

Eggshells, for example, are great if your soil is low in calcium, as most soil in New England is. Crumple them and add them to your planting holes, or just put them in your compost bin.

I also recommend using kelp extract, or kelp/fish extract, when you transplant plants, plant bulbs, or start new seeds. Kelp contains plant rooting hormones and lots of micronutrients, so it helps roots develop quickly. Fish extract is a general fertilizer, but probably less necessary.

Are you growing beans, peas, soybeans, clover, or alfalfa for the first time? If so, your soil may not have enough of the critical nitrogen-fixing bacteria that attach to the plant roots, form nodes, pull nitrogen out of the air, and make it available to the plants. In a new garden, therefore, I recommend bacterial inoculants (different ones for different plants) that help ensure healthy node production and nitrogen fixation. They seem like good insurance to me. In an established garden that has been growing nitrogen-fixing plants, however, they are unnecessary.

The following supplements can also be useful:

➢ Lime. Lime is mined, so I encourage you to use it only if soil tests indicate you need it in a particular location, for a particular plant (some plants prefer acid soils), and you care about maximum productivity. Fedco sells hi-cal lime for soils with excess magnesium and dolomitic lime for soils that need magnesium or where magnesium isn’t a problem. Your soil test will tell you which to use.

➢ Agri-gel. This polymer absorbs and releases water. I recommend it for container gardens and for new transplants of shrubs and trees. It isn’t “organic,” however, so don’t use it if you care about having an organic garden.

➢ Fedco’s “fall fruit tree mix”. If you plan to plant a tree you really care about, this mixture of organically-certified soil amendments will help it thrive. Spread the mix on top of the soil in a 4-6’ diameter, and cover it with compost and chipped branches (to encourage the growth of beneficial fungi). Let it sit all winter. Then plant your tree in the spring. Or use the planting mix as a top-dressing for established trees.

➢ Cover crops – e.g., field peas, crimson clover, winter rye. Cover crops add fertility and structure, and prevent erosion, but may require digging and good timing. They are a staple for organic and biodynamic farmers.

Some comments about chemical fertilizers etc. …

Nitrogen is one of the primary constraints on how much life, which biologists call “biomass,” is possible. Nitrogen is a key component of protein, and without protein living things can’t grow.

For most of the earth’s history, nearly all of the biologically-available nitrogen had been “fixed,” or made usable for living creatures, by bacteria, and a small bit by lightning and other rare events.

Now, however, more than half of the world’s biologically-available nitrogen has been fixed chemically, by processes invented about a hundred years ago that were turned towards making artificial fertilizers after World War II. The human population has grown much larger than it could have under the previous nitrogen constraints. Indeed, the “Green Revolution” of the 1960s and 1970s was largely a matter of bringing chemical fertilizers to parts of the world that had been straining the productivity of their local ecosystems. Some estimates suggest that about 40% of the human population is now alive because of chemical fertilizers.

But we are conducting a massive experiment. What happens when a planet suddenly loses its nitrogen constraints on biomass? What then happens when soil communities become so damaged that nitrogen fertilizers are no longer effective in keeping up crop yields? What happens when every bushel of corn requires a quarter gallon or even half gallon of oil to grow it, and oil gets rare and expensive?

This is one of the reasons why organic farming is important. Done well, organic farming and what is now known as “conventional” farming (but didn’t exist a lifetime ago) often have comparable yields from a given amount of land. Organic farming, however, has the potential to increase soil fertility over the years, while chemicals-based farming nearly always depletes it. Chemical fertilizers, herbicides, and pesticides kill many parts of the soil community. Pesticides and herbicides are, of course, intended to kill, while chemical fertilizers are so concentrated that they kill microbes in the soil. The result is that the soil becomes increasingly infertile over time, so people have to use more and more of the chemicals to keep up yields.

For a farmer, it’s a terrible dilemma: once you start using the chemicals, you are dependent on them for your income, but you have to use more and more – and pay more and more – as the years go by. As the soil is depleted of humus, it is more vulnerable to erosion by wind and water. Eventually soil becomes so burned and sterile that it may not sustain crops at all. Transitioning to organic or biodynamic methods of farming, however, takes time and experimentation to adapt the techniques not just to each farm and crop, but to each area of a farm. Many farmers live too close to the edge to happily take on that sort of risk.

For a home gardener, it seems simple to me: Don’t use chemical fertilizers, and use herbicides and pesticides very carefully. (I, for example, am terribly allergic to poison ivy, so I had someone else carefully apply herbicides to a great big poison ivy plant in my yard.)

In the bigger picture, we need to develop and maintain sustainable approaches to farming if we want to have a stable food supply in a generation or two.

Next page: Compost