Each mushroom species deals with rain differently
The Sportsman’s Report
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By Bill Hanson  September 20, 2013 12:00 am

One thing I’m often asked on mushroom forays by beginners is how much rain stimulates growth and how soon after a rainstorm do we find newly grown fungi. A mushroom is the fruiting body of an underground plant/animal called a mycelium. Think of an apple tree, the fruiting body is an apple, half of the apple tree lives above the ground, half below. 

Like a mushroom, some apples are better than others to eat. Unlike apples, some mushrooms are deadly poisonous and some are very tasty. Back to the rain, if the mycelium feels that conditions are right, it will flower and a mushroom is born.

How much rain does it take? Different species respond differently, as many desert mushrooms respond within a few days of rain, some within hours. In my opinion, it is dependent on the condition of the mycelium before the rain falls. If the mycelium is already about to fruit, then there will be a quick response. If still in slumber mode, then the rain will stimulate growth more slowly.

If a mycelium has already fruited and mushrooms are up with some fresh and some in the soggy, rotten end of their time, then the rains evoke a different response. In those already up, the rain will be absorbed and the mushroom will be water logged but can spring back to be solid and fresh. Those that are already past their prime turn into goo. New mushrooms sprout from the mycelium within a few days of a good rain if the mycelium is still in the fruiting mode. Yet, they might remain tiny little specimens for a while, a week or more, then unfold into a healthy, spore-bearing mushroom.

Different mycelium fruit at different times, depending on the time of year, surface temperature, conditions on/in the ground and other factors, including rainfall. Mushroom hunters know from experience when to look for different species at different times of the year. In the fall, when heavy rains come, the mycelium of several mushrooms wake up and send up their fruit/mushroom. One of the choice edibles we like to catch in the fall are the Boletus Edulis or ‘Porcini.’ It often looks like the British common name, ‘Penny Bun’ with a soft-brown cap and a heavy stem. So far, this mushroom has been resistant to commercial cultivation, so any time you see a packet of dried ‘Porcini’ it has been harvested in the wild, sold to a field agent, then to a broker, then to the processor to be cleaned and dried to a fragrant, dark and dry chip. Boletus grow in many countries, and in parts of Europe and Scandinavia, the Boletus Edulis are so robust that they are collected and sold for the commercial market.

For our area, the Boletus are stimulated by a few days of good, hard rain. It takes 10 days to two weeks for the little mushroom ‘buttons’ to push up through the forest floor, ‘Duff’ in mushroom speak, and are ready to harvest. Other myceliums are stimulated by the cold days of mid-winter, others by spring time weather.

I recommend you join a mushroom club. Just Google it to find the nearest group and tag along on club forays. Your first mushroom book should be, “All That the Rain Promises and More” by David Arora. It is the field guide companion to his much bigger book, “Mushrooms Demystified.” The book “Rain” is about $18, the big one in the $45 dollar range and a bit much for the beginner.


Bill Hanson is a Sonoma County native and a lifelong sportsman. He is the former president of the Sonoma County Mycological Association. Look for his column in The Community Voice each week.

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