With the recent rains, the reproductive caps of soul fungi are popping up in area lawns and gardens.  Almost all are highly poisonous and should not be eaten by people or pets.

Anytime the weather turns warm and humid it is common to see a toadstool or two poke up from our lawns, gardens and even bare ground.

Our recent rounds of rain have triggered all kinds of interesting phenomenon including the emergence of fungal mushroom structures, sometimes called toadstools. When they appear, questions abound. “What causes their growth?” “Are they poisonous?” “What should be done with them?”

Mushrooms are the reproductive, spore-producing structures of specific types of fungi that live in the ground. These fungi are beneficial because they break down organic matter in the soil and release nutrients that are necessary for plant growth. They are dangerous in that almost all of them are highly poisonous, even fatal if eaten.  

Sometimes pets and possibly children get sick from taking a bite out of a mushroom. For that reason, it is a good idea to promptly remove them if there is any question. However, if they are in a place where they are not likely to cause a problem, it is perfectly okay to leave them so that they can complete their important ecological function.

There are many fungi that show up this time of year. In addition to the common mushrooms that we often see in our lawns, we can sometimes find the less familiar puffballs and slime molds. I usually see the puffballs out in the desert or sometimes on bare ground. I found a slime mold growing around the base of one of an iris plant the other day. None of these cause harm to other plants. They simply decompose dead plant matter in the soil, a really important job.  

The mushrooms show up during the summer rainy season because the spores, the “seeds” of the fungus, germinate best when the temperatures are warm, the humidity is high and the soil slightly moist. The dry, hot month of June would not help the fungus achieve effective reproduction so we do not often see them then. The warm temperatures, the high humidity and the rainfall all work to initiate the reproductive cycle of these fungi. When conditions are right, up they pop to do their thing.

There are many different types of fungi in the world. Some are one-celled and microscopic. Examples of these would be the fungi that cause root diseases in over-wet soils. Others, like the mushrooms, are larger and quite complex.

A few fungi are plant or animal pathogenic; that is, they cause diseases in living plants and animals. The vast majority, however, are simply silent partners as they go about their business of quietly breaking down dead plant materials into their component parts.

The mushroom that we commonly see in our lawns and gardens is really interesting in that it has a quite unique structure. Basically, it consists of three pieces: a bulb-shaped base down at the surface of the soil, a stalk emerging from the base and an umbrella-like cap which sits on the top of the stalk. The top of the mature cap is usually whitish tan to yellow brown in color. The nearly white stalk can be between 4 and 8 inches tall.

The cap is where the actual reproductive work is done. Tiny seed-like spores are produced in the gills, the groves that are on the bottom side of the cap. When the spores are released from these gills, they easily blow away in the wind to be ready to germinate and grow when conditions are right.

Upon germination, the new fungus sends out long, thin threadlike growths called hyphae. These strands are the everyday workhorse part of the fungus and their thing is to decompose wood, fallen leaves, lawn thatch and other organic matter in the soil. As they break down their food sources, they absorb a portion of the released nutrients from the decomposed plant material.

A single strand of hyphae is usually too small to see without a magnifying glass, but during times of reproduction, the individual hyphae strands begin to grow together in the soil to form masses called mycelium. When the mycelium has developed sufficiently, mushrooms are produced. The mushroom-producing fungi can live in the soil for years and produce mushrooms whenever the weather is favorable.

Is there a way to prevent them from growing in our yards? There are no chemicals currently that are effective in controlling or preventing the growth of mushroom-producing fungi. Insecticides, weed killers and even fungicides are not effective. To stop the mushrooms, we have to eliminate the material upon which they grow. That can be pretty tough to do because you never know where they are going to pop up next.

In Southern Arizona, we generally see mushrooms growing on excessive lawn thatch, the matted dead layer laying on the surface of the soil or where dead leaves have accumulated over time. The best thing to do in this case is to de-thatch the lawn or remove the dead leaves. Since de-thatching removes the fungi’s food source, the number and frequency of the mushrooms should decline or stop altogether.   

The easiest solution, since their emergence is so erratic and hard to predict, is to simply watch for them out in the yard and then remove them before letting the pets or children out into the yard. Some people simply use the toe of their shoe to gently kick them loose and them put them into a trash bag. A better way might be to use a garden digging tool and cut the mushroom loose as close to the ground as possible. This ensures that the base as well as the cap and stalk are removed.

The common mushroom or toadstool growing in our lawns and gardens, along with their many relatives, are all members of the fungi group. While most are poisonous, they rarely cause plant diseases or injury. As they decompose existing soil organic matter, they perform a valuable role in the ecology of the desert. If they pose a possible health problem to pets or children, they can be easily removed and discarded into a safe place.

If you have questions, you can reach one of the Master Gardener volunteers at the Cooperative Extension office, 820 E. Cottonwood Lane, Building C, in Casa Grande. The telephone is 520-836-5221, ext. 204.

Rick Gibson is an agricultural extension agent and the director of the Cooperative Extension in Pinal County. He can be reached at 520-836-5221 ext. 227 .