Gardening and fungus go hand-in-hand. Whether you love fungi or hate them, our gardens and dishes just wouldn’t be the same without these bizarre and fascinating things around. They recycle the nutrients in our wild lands as well as our cultured spaces, make food from waste, and latch onto the root structures of around 90 percent of the world’s vascular plants, helping them absorb water and nutrients. There’s a whole lot more they can do for us, too, but this discussion will focus on just a few of the fungi we find in our gardens or on our plates.
Fungi are constituents of a vast kingdom with an astonishing variety of forms and functions. Some have large fruiting bodies (which we call mushrooms, also known as macrofungi) that are easy to see, while others (like mycorrhizae) stay hidden in the soil or remain dormant for years. Some fungal species are essential for the survival of certain plants, while others can wreak havoc on our gardens or cause sickness in people and animals.
The desert Southwest isn’t thought of as a place where fungi thrive. Compared to warm environments with ample moisture, where mushrooms and jelly-like things seem to grow on every available surface, the lowest elevations of Baja Arizona feel virtually fungus-free.
Despite all appearances, there are more than 2,200 species of fungi documented in Arizona, and some estimates suggest that there are at least several thousand more that haven’t been recorded yet. A greater variety can be found as you go up in elevation, and you’re more likely to see larger mushrooms as you get closer to the sky islands, but there’s more going on in the gardens of the low desert than you might have thought.
Mycorrhizae isn’t a new word in gardening vocabulary. From the Greek words for “fungus” and “root,” these fungus-roots live in the soil and form mutually beneficial relationships with the roots of living plants, taking some of the plant’s self-manufactured food in exchange for an upgrade in the plant’s ability to absorb nutrients and water.
It was just a few years ago that I first witnessed a gardener inoculating the soil with mycorrhizal fungi, but such a scene is almost common today. From pretreated seeds to dry mixes, dips, or water-soluble mixes, you don’t have to go far to find products aimed at instilling and nurturing these beneficial fungi, or gardeners eager to purchase them.
Ideally, you already have at least several kinds of mycorrhizal fungi living in your soil, but land development practices and standard garden activities like tilling can set them back. Reported benefits of good mycorrhizal activity include larger plant growth; better disease, pest, and drought resistance; improved soil structure (and thus water retention); and protection from some types of harmful fungi that might move in if the soil weren’t already occupied.
We’re still learning about the complex relationship between plants and mycorrhizal fungi, and scientists aren’t all in agreement about the benefits of using inoculants. Some plants appear to appreciate the effort more than others, and the different types of fungi found in available inoculants are not all equally effective in every garden. The most drastic positive impact from inoculant use is seen in severely nutrient-poor soils, while a well-mulched, compost-rich garden bed (where good fungi may already be thriving) might show little difference at all.
If you want to give it a try, look for an inoculant mix from a reputable dealer that contains endomycorrhizae, as this class of mycorrhizal fungi is more beneficial to fruits and veggies (ectomycorrhizae are more beneficial to woody plants like oak, pine, and eucalyptus). Unless you’re using reverse osmosis or well water, allow water for inoculant mixing to sit for a day to give any chlorine time to break down. Inoculate soil in spring or fall, when plant roots are actively growing, and use organic fertilizers that are low in phosphorus (the middle number on the fertilizer’s label) while your new fungal friends are getting established for at least 30 days.
Unfortunately, this is the group of fungi that gardeners in the low desert are probably the most familiar with. We’re lucky that our dry heat keeps many types of fungus in check for much of the year, but it can be hard to keep some of them from taking over when the conditions are right. Fungal outbreaks tend to occur when temperatures are relatively low and humidity is high. However, these pathogens are numerous and diverse, and they’ll quickly take any opportunity that presents itself if they have what they need to grow (a susceptible host, the right temperature, high humidity, and moisture).
There are some easy cultural practices that can help keep fungal infections from spreading, but it’s important to catch problems and deal with them early. Remove the affected plant if possible, or the affected leaves and/or branches. Consider doing some extra pruning or thinning in the area to increase light penetration and airflow. Lift sprawling plants off of the ground with cages or trellises to limit their contact with spores in the soil.
Soil-borne spores can also splash onto leaf surfaces when watering with a hose or even a watering can, so use an alternate watering method like drip irrigation or ollas when trying to get an outbreak under control. Keep beds as tidy as possible, especially through the winter; spores like to spend the colder months hiding out in the leaf debris at the base of your plants. Crop rotation is a good idea for many reasons, but it’s essential if you discover a soil-dwelling fungal infection in your garden. You’ll also want to stick with crop varieties that are resistant to fungi that you’ve had problems with, as parasitic fungi or their spores can stick around for a long time once they show up.
As a last resort, there are a number of fungicides at our disposal to treat a persistent outbreak, or use as a preventative treatment, but keep in mind that fungicidal treatments will likely affect the good fungi as well as the bad. In addition, a fungus that grows and spreads quickly can build up resistances to treatments that aren’t 100 percent effective, so it may be necessary to alternate your modes of attack by switching between two or more types of fungicide that are specified to treat the type of fungus you’ve got.
It turns out that you don’t have to go mushroom hunting on one of the sky islands to find good edible mushrooms in the desert. I talked with John Jacobs of the Sonoran Mushroom Company, who said that while operating a large-scale mushroom growing company is a complicated endeavor (especially in our climate), growing a few at home is fairly easy. They’ll grow year-round indoors, and don’t have to take up too much counter space.
Jacobs recommends starting with a mushroom growing kit if you’re interested in growing mushrooms at home. Packaged with everything you need for the “flavor” of your choice, all you have to do is follow the directions, spray with water when necessary, and harvest. The kits are easy to find locally and online for around $13-$30, depending on brand and flavor. If the first kit works out and you liked the experience, till the straw from the spent kit into your garden and try a different flavor the next time around. Oyster mushrooms seem to be the most commonly available, as they’re one of the easiest to grow, but kits with other mushrooms like shiitake or portobello are out there, too.
According to Jacobs, the real fun commences when you start experimenting with mushrooms you’ve never grown before and trying different types of substrates to grow them in (like straw, sawdust, or coffee grounds). Jacobs’ whole family, and especially the kids, love to see what each new variety will look and taste like, and how different substrates can affect growth and flavor. One of his personal favorites is the Italian oyster mushroom, which has a rich, buttery flavor, but he loves it when they have good luck with a crop of golden oyster mushrooms, which are more finicky but taste delicious.
Inoculants for a wide variety of species can be found online, but each type of mushroom comes with its own set of light, water, and substrate preferences, so it’s a good idea to do a little research before purchasing, and use a reputable dealer. Several sources have pointed me in the direction of Fungi Perfecti, which is a great informational resource as well as a premier source for spores.
If growing your own mushrooms at home sounds like too much effort, find mushrooms grown by the Sonoran Mushroom Company at Time Market and Rincon Market in Tucson, and at their booth at the St. Philip’s Plaza Farmers’ Market on Sunday. ✜
Amy Belk is a garden writer and photographer, a certified arborist, and a certified nursery professional who has been learning from her garden for 16 years. She and her husband homestead on a little piece of the desert in the heart of Tucson.