In the Garden

with Kerry Heafner

Louisiana’s warm and humid climate sets the stage for an impressive array of mushrooms to be observed, and the roles they play in our gardens and both natural and cultivated landscapes cannot be underemphasized. So, this month, let’s look at some of our fleshy fungi.

What exactly is a mushroom? Any mushroom is simply the spore-producing structure of a fungus classified as a basidiomycete. This means the fungus produces its spores on microscopic structures called basidia. A single basidium with the spores on it looks rather like Jughead’s hat and if you get that reference, then you’re old. Mushrooms typically don’t last more than a few days. When certain environmental parameters like soil moisture and nighttime temperatures are right, mushrooms emerge, oftentimes in a matter of hours, throw their spores, then die away. The rest of the fungus is in the soil or potting medium, so we never see it. Out of sight, out of mind. Microscopic spores are carried away by air currents, land in a suitable habitat, and start a new mycelium in the soil. Spores of two mating types (+ and -) are required for mushroom, and therefore spore, production. Mushrooms that have gills on the underside of the cap are called agarics. If it has pores instead of gills, then it is called a bolete. Many fleshy fungi don’t resemble mushrooms at all. Some look like coral from the sea, blobs of jelly, brains, or even a slice of beef liver. There are even mushrooms that glow in the dark! 

Some gardeners freak out when they see a mushroom growing in a flowerpot or in a bed. But mushrooms themselves are harmless to most garden plants. Bracket fungi, or mushrooms growing out of live trees, are a concern, however. In fact, having fungi like that in your soil or potting medium is a good thing. Ecologically, fungi are important as decomposers. Imagine if all the leaves dropped by deciduous trees every fall never decomposed. Fungi help turn those dead leaves back into nutrient-rich soil. During decomposition, nutrients tied up in leaf tissue are made available once again to other plants. Fungi do the same thing in our gardens and especially in compost piles. All the straw, hay, grass clippings, wood chips, or dead leaves used as mulch this year will be soil in coming seasons thanks to fungi. 

Fungi do something else that is vitally important for plant health. Fungi form symbiotic relationships with roots and allow plants to take up nutrients, especially nitrogen and phosphorous, from soil more readily than they would otherwise be able to.  These beneficial associations are called “mycorrhizae,” which literally means “fungus root.”  Plants ranging from oak and pine trees to Bermuda and St. Augustine grass rely on mycorrhizal fungi for this exact purpose. This plant/fungus relationship was established when plants first colonized land and has remained a vital component of land plant evolution. This is one reason the species of mushrooms found in any given habitat, from lawns to woods, can be predicted. For example, the deadly “destroying angels,” Amanita virosa and related species, occur here in the ArkLaMiss under oak and pine trees with which they are mycorrhizal. They are solid white, even the gills (hence the “angel” part of their common name) and will have a ring around the stalk. They will also be sitting in a little fungal cup that occurs either at or just below soil level. While they are deadly poisonous to anyone or anything that ingests them, they are biologically beneficial to the trees under which they are growing. Other than being admired for their haunting beauty, they are best left alone. 

Several less dangerous fungal species that mimic Destroying Angels are to be found here in the ArkLaMiss. One is called “The Vomiter” (Chlorophyllum molybdites), a large, white mushroom occurring in lawns. The gills under the cap turn sea-green momentarily after being picked. While The Vomiter is a toxic species, it is not deadly poisonous. It will simply live up to its nickname. Another solid white mushroom that colonizes lawns is a close cousin of Destroying Angels, but information on its toxicity is ambiguous. I’ve photographed Saproamanita thiersii in Monroe’s Garden District in a grassy area off Stubbs Avenue. As the genus name suggests, this species is not mycorrhizal. Rather, it is saprophytic, meaning it decomposes dead thatch and the grass clippings that are left after the area is mowed. Its shaggy appearance is distinctive, but its solid white color is also a red flag. When in doubt, toss it out. 

Relatives of the grocery store mushroom, Agaricus bisporus, are also in Louisiana’s fungal flora. Agaricus species have gills that turn from salmon pink to chocolate brown after being picked or after the spores have been discharged. The next time you buy fresh mushrooms at the grocery store, look at the gills. They’re brown and this immediately separates them from the dangerous Amanita species.

Chanterelles are much sought after by foragers and fungal aficionados, and Louisiana has plentiful populations. One of the more oddball fungi is Bird’s Nest Fungus, genus Cyathus. The “eggs” in the nests are called peridioles and contain the spores. Bird’s Nest Fungus is another example of saprophytic life history. They break down organic matter into nutrient-rich compost from which our gardens and landscapes benefit.    

Of course, a lot of folks are interested in whether a mushroom is edible or not. Bottom line, never eat a mushroom you’re unfamiliar with or that you don’t have a positive identification for. As mycologist and author David Arora writes in Mushrooms Demystified (Ten Speed Press), some mushrooms are “better kicked than picked.”  But, before you punt that toadstool across your lawn, think about the fact that that fungus simply means you have healthy soil. Consider yourself lucky!