Mushrooms are a welcome sign of a healthy garden
When mushrooms appear, smart gardeners welcome them. “It tells you that you have healthy soil,” said Stephanie Adams, a plant pathologist at The Morton Arboretum in Lisle.
Mushrooms are a sign that your soil has plenty of organic matter and a bustling community of underground organisms. Soil that supports many different forms of life is a good home for plants, a place where their roots will benefit from the nutrients and other services provided by fungi, bacteria, invertebrates, and many other inhabitants.
The mushrooms you see are the short-lived fruiting bodies of certain kinds of underground fungi. They only appear when conditions are right for the fungus to reproduce, usually when it’s moist. Autumn rains often bring mushrooms.
Though mushrooms are temporary, the fungus they grow from is there all the time as a large network of microscopically slender threads called mycelia growing through the soil. “Sometimes, if you pull back old mulch, you may see really fine white threads growing through it,” Adams said. “Those are mycelia.”
The network of mycelia does the work of the fungus, breaking down dead plants and other organic matter to enrich the soil and releasing their chemical components to nourish plants. “The fungi need organic matter to live, so the mushrooms are a sign that there is organic matter in your soil,” said Sharon Yiesla, plant knowledge specialist in the Arboretum’s Plant Clinic.
These soil fungi are nothing to be feared. “They aren’t the same fungi that cause plant diseases such as powdery mildew and cedar-apple rust,” Yiesla said. Instead, they are the major composters that populate soils all over the world, breaking down fallen leaves, stalks, dead branches, and other organic matter to improve soil.
Mushrooms are often seen growing in mulch. “The shredded wood or leaves that we use for mulch are food for fungi that are slowly consuming it,” Yiesla said. That slow decay is one of the benefits of mulch.
“You want that organic matter to break down for the future of your trees and plants,” Adams said. Gardeners can also add organic matter by top-dressing the soil with compost, by digging in compost when starting a new bed, and by leaving as many leaves as possible in autumn for soil fungi to consume.
What are mushrooms for? They are a fungus’ way of distributing its reproductive spores to colonize more areas of soil. Since the tiny spores can’t travel by themselves, they must fly on the wind — and to do that, they need to be in the open air. A mushroom that grows even an inch or two out of the soil lifts the spores high enough that a breeze might catch one and loft it away to fresh soil to start a new mycelium network.
Mushrooms last only long enough to release their spores and then quietly dry up or dissolve over a few days. They do no harm to any of the living plants in your garden, Yiesla said. “If mushrooms annoy you, you can rake them away,” she said. “Just don’t try to kill them with any kind of chemical. That would damage the fungi in your soil, and those fungi are good for your plants.”
Since a few species of mushrooms are toxic to eat, it’s not a good idea to pluck them for the kitchen.
“It’s hard for nonexperts to identify mushrooms with certainty,” she said. “To be on the safe side, get your mushrooms at the supermarket.”
The only time a mushroom might be a sign of trouble is if it is growing out of the trunk or roots of a living tree, or from the soil right around a tree. “That can be an indication that there is decay inside the wood of the trunk or roots,” Yiesla said. “Have a professional inspect and evaluate the condition of the tree.”
Yet most mushrooms are benign. They are happy messengers from the underground ecosystem. “You’re doing good work,” the mushrooms say. “Keep providing us with organic matter and we’ll keep feeding your plants.”