A healthy organism is active, doing the job it is designed to do and working in concert with the right partners. Soil health means that the organisms in the soil are present and doing the job they are supposed to be doing. The soil in a healthy garden is a very active place.
Bacteria are single-celled organisms that cycle nutrients in the soil. There are thousands of species of bacteria.
Generally, the beneficial types are aerobic, they need oxygen to survive. The bad guys, the disease-causing ones, thrive in low-oxygen environments. Our good guys are vultures. They eat the dead plant matter and concentrate the nutrients in their bodies. They bind all kinds of compounds into organic forms that won’t leach out of the soil.
Another good bacteria collaborates with legumes like your peas to “fix” the nitrogen in the air and adds it to the soil.
Fungi are strand-like microorganisms that help to hold the soil particles together to improve soil structure. Some are very specific to a plant, like the type that feeds trees. This fungi establishes a mutually beneficial mycorrhizal relationship with plants and trees to hold and transfer nutrients directly to the plant’s roots. This is why, when you dig up a tree or shrub, you should take as much surrounding soil as possible so the roots and fungi can immediately continue their partnership. Fungi “eat up” harder to digest organic materials like dead leaves, pine needles and fallen tree trunks.
Our third soil helper is protozoa. These are microorganisms like flagellates, amoeba and ciliates. You don’t need to know who these guys are, only that they eat bacteria. When they do, they release excess nutrients in soluble forms that the plants can use. They also team up with fungi and bacteria to build spaces in the soil so oxygen, water and roots can move through the soil more easily.
Nematodes have a bad press. Most people think of the root eating ones. Most of the small worm-like critters actually protect plant roots from disease, help build soil structure and release nutrients in a soluble form to feed plants right in the root system.
Then there are the soil dwelling insects, the microarthropods. This includes soil mites and springtails. There are quite a lot of these critters. Their job is to eat fungi or each other to release nutrients in a plant available form. They also help build soil structure.
To a large extent, plants control and select the microorganisms they need for proper growth. For the healthiest soil we need some members from each of these groups working with each other. Using heavy applications of fertilizers or weed killers can do a number on your soil populations of beneficial critters.
One good way to feed your soil is to use compost, beneficial organisms will thrive and help maintain aerobic conditions of the compost when you dig it into your garden. Compost piles are not noted for adding to the beauty of your yard. Hide them behind a shrub or a fence if you can.
A healthy compost pile will not smell. If yours stinks, you are doing it wrong! Be careful of the type of poop you add. No cat or dog droppings. Horse apples can be full of weeds and need a hot pile. Make it easy on yourself and get the commercial bagged stuff.