Healthy soil is much more than a collection of mineral particles of the right size and shape. And soil fertility is much more than proper pH or balance of NPK. There's a world of biology going on in fertile soil. Some of that biology is fungus. And a lot of that fungus is helpful, even essential, to plants. Fungus creates structure in soil, moves nutrients around, and works with other good soil critters and against some bad ones. That's impressive for something you've never noticed.
These cute red mushrooms indicate the presence of certain fungus. Leaf litter is a good fungal food source.
Mushrooms are a minor part of the fungus that inhabits your soil. The fungus was present before the mushroom formed, and was still there when the mushroom shriveled up. The real "body" of many soil fungi is made up of hairlike strands you've probably never noticed. You might think of fungus as an organism that's "all roots, occasional flowers (mushrooms) and no leaves." The microscopic rootlike portion of many fungi are called "hyphae" ( pronounced HIGH-fee).) Hyphae grow like incredibly thin roots, searching out organic matter to eat. You may HAVE seen fungal hyphae, when they multiply so thickly that they form a furry white mass on wood mulch or wads of brown leaves. Some fungi eat dead leaves and wood, others eat live things like nematodes (another unseen but often problematic soil life form.) There are fungi that live intimately with roots of green plants, helping both partners to thrive.
Healthy soil fungi do fantastic work in your garden
Soil fungi have multiple important roles in your garden. Those that break down organic matter are the "heavy lifters" in the compost pile and soil. Fungi do the hard work of chewing up tough wood fibers and cracking open protein-based insect shells. When a fungus grows, its hyphae reach out and capture nutrients from organic matter. The nutrients are moved around in the soil as they are conveyed throughout the fungal mass. The digestive action of fungus creates sticky substances that make soil hold together in "crumbs" instead of pasty mud. Some fungi grow intimately with plant roots. These mycorrhizal fungi are critical to helping many plants absorb nutrients. Some fungi actually trap and destroy nematodes. And individual soil fungi die, while others are growing. Death of a portion of soil fungus means the release of nutrients in its cells within the root zone of plants. And dead fungal hyphae leave tiny channels in soil. Those spaces form tiny cavities to shelter bacteria, or tiny tunnels that let air and water flow in the soil.
Soil fungus is great! How can we grow more of it?
Fungus is living in your garden soil already. With a little help, it will multiply, though you still may not see it. Healthy perennials, trees and shrubs, and crumbly, rich, woodsy smelling soil will all testify to the presence of good soil fungi.
Feed it mulch and compost - Fungus eats tough organic matter. Use organic mulches in the garden. Anything that comes from a tree is ideal for fostering fungi. Top your soil with pine straw, hardwood or bark mulches, fall leaves from deciduous trees, or compost made with plenty of these items.
Stop mechanically tilling - Power tilling puts soil and fungus into a 'food processor" and creates a mushy puree of pulverized fungi and soil particles. Use hand tools to turn soil and mix fungal food sources into it. Compost and mulch on the surface is available to fungi below. Fungi will grow up into the surface, digest that organic material, and bring those nutrients down into the root zone. After all, nobody tills the forest, and its fungus rich layer of leaf litter supports massive trees and a huge variety of understory shrubs and plants.
Buy mycorrhizal fungi, if appropriate - Shop for mycorrhizal fungi products, checking the label for recommendations for your specific types of plants (there are several kinds of these fungi, different plants use different kinds, and a few plants really don't use them at all.) Also use the products according to directions.
Stop or minimize use of chemical fungicides - Here's a no brainer: using chemical fungicides anywhere in your garden can harm soil fungi. Use them carefully or try alternatives.
Use cover crops and crop rotation - Bare soil means no plant roots, no plant roots means a period of famine for mycorrhizal fungi. Grass and legume cover crops do more than capture nitrogen. They provide a winter haven for many soil fungi. Come spring, the soil has a lively group of fungi and plentiful organic matter to keep them in the pink (white?) In vegetable gardens, crops of the onion, bean and corn families are good partners to soil fungi. Crop rotation moves these plants around year to year. Good soil fungi are kept happy throughout the vegetable garden.