Harefoot mushroom (Coprinopsis lagopus) is typically found in wood chip mulch or duff. Layering compost or wood chips on top of garden beds is one of the best ways to improve your soil and support beneficial fungi.

Photo courtesy of Katherine Darrow

Barbara Faurot

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Fungi are at the heart of life in the garden. They are neither plants nor animals, but they are essential to all plant and animal life. 

Fungi were among the first complex, multicellular life forms on land, hundreds of millions of years ago. They provided essential minerals for land plants that enabled them to grow and spread. 

Mycologists estimate that there are more than 5 million species of fungi on earth. Their key function is to break down dead and decaying organic matter and release nutrients that are available to plants.

The vast majority of fungi in the garden are beneficial to plants. In fact, most trees, shrubs, grasses, annuals, and perennials depend on some type of fungal relationships. The fungi help create soil structure, enable nutrient exchange, support beneficial soil microorganisms, and break down certain pesticides in the soil. Some fungi even help control root knot nematodes and suppress soil-borne pathogens to protect plants from root diseases. 

Underground, fungi take the form of hyphae — thin, rootlike filaments that connect in a complex mycorrhizal network that mycologist Paul Stamets has called “the neurological network of nature.” The hyphae are shared between plants as they form relationships with roots in the soil. Fungal hyphae can multiply and create a thick mass that is often visible in soil, or on wood mulch or duff. 

Plants provide sugars and essential chemicals to the fungus, while the hyphae filaments burrow into the soil to pick up nutrients and water for the plants. The filaments attach to roots and reach far into the soil, expanding the surface area of plant roots up to a thousand times. This vast network helps plants survive drought and other stresses. 

Mushrooms are the above-ground fruiting bodies (the reproductive structures) of fungi that live in the soil. When environmental conditions are right — for example, periods of wet weather — the fungi will send up these fruiting structures to help them reproduce by dispersing windblown spores. The mushroom is actually formed of hyphae, but in a more dense configuration than the underground threads. 

As with the fungi overall, the vast majority of mushrooms are beneficial and do not damage lawns or gardens. Removing the mushrooms from a lawn, garden bed, or forest does not affect the fungi in the soil, but it will reduce the number of spores released to expand the mycorrhizal network.

Once spore dispersal is complete, the fungus no longer needs the fruiting body, and it disappears. The fungal mycelia, which are masses of hyphae, are still growing in the soil. The fungus will persist as long as there is plenty of organic matter to feed on. Layering compost, leaf litter, or coarse, organic mulch on top of the soil are great ways to feed your fungi. 

Many companies offer manufactured mycorrhizal inoculants, but research by WSU and others shows that there is no reason to purchase them. Garden soil already contains hundreds or thousands of fungus types. Manufactured mycorrhizae usually consists of only a few. They are often heat sensitive and, as a result, may have limited shelf life. 

It is also possible that the purchased inoculants include species from an area that is foreign to your soil. In special cases where you want to add mycorrhizae to sterile potting soil or bare soil that has no natural fungi, it is nearly always better to add compost, which contains several hundred species of local fungi, bacteria, and other microbes. 

On occasion, fungal diseases such as powdery mildew or leaf spots and blights can infect plants. The best overall mitigation approach is to remove affected branches, foliage, and debris. Clean and sterilize tools before and after pruning. Space plantings and prune them, if needed, to provide good air circulation. 

Avoid over-watering and over-fertilizing, which can damage beneficial soil fungi and also promote fungal disease. Widespread use of fungicides is not recommended, as they are largely ineffective and can damage soil fungi. If you do decide to use a fungicide, it should be targeted only to the specific plant problem. Useful information on fungal diseases and remedies can be found at hortsense.cahnrs.wsu.edu.

Above ground, decay fungi can affect wood strength in older or weaker trees. The decay may be hidden, unless a cavity, bark wound, or fruiting body is visible. Affected trunks and limbs can become a safety hazard, especially when stressed by wind or heavy rain. It’s a good idea to observe older trees for possible decay and, if needed, consult a certified arborist for mitigation options. 

In addition to its primary functions of nutrient cycling, the mycorrhizal network also stores vast amounts of carbon underground that would otherwise be released into the atmosphere as carbon dioxide. Creating a welcoming environment for your soil fungi can make a big difference — one garden at a time. 

Important note for mushroom foragers: It is, of course, essential to be certain of your ID before consuming, as many edible mushrooms have poisonous look-alikes. The Puget Sound Mycological Society is one resource for information and tools; psms.org.

The fourth of six educational talks in the Master Gardener Foundation’s Virtual Yard & Garden Lecture Series is from 10 a.m. to noon Saturday, March 11.

Del Brummet, head gardener at the Elisabeth C. Miller Botanical Garden, will cover “Plants for a Better Planet With Great Plant Picks.” Information on all speakers, topics, and tickets is available at jcmgf.org/yard-and-garden-series. 

Barbara Faurot is a Jefferson County Master Gardener and Master Pruner, working with other volunteers who serve as community educators in gardening and environmental stewardship.