Does winter snow make shrooms grow?

By Ellen Jacobson, CMS Sociologist

Well, yes, maybe, sometimes, never, always, often, probably and only in even numbered years. If winter snow does not make mushrooms grow, exactly what does make mushrooms grow? In an article that I cannot find, I read that mycologists in Sweden had done a study on the appearance of mushrooms after rain and found that DEPENDING ON THE TEMPERATURE, mushrooms tend to appear about four to 10 days after a rainfall. Colorado is not Sweden, however, and what follows are my very scientific and personal observations on the relationship between rainfall, temperature, and the subsequent fruiting of several species of mushrooms.

In the spring, we all eagerly await the first fungi of the season, the almost sacred and definitely glorious golden morel. I see no relationship between the amount of winter snow and the growth of morels. I do find that April and early May rain followed by warm but NOT HOT weather encourages morels to grow. If the rain stops before mid-April or a heat spell arrives, the morels dwindle. If the rains continue, but the weather gets hot causing the soil temperature to rise, the morels dwindle. So, even if the ground is moist, if the soil temperature is too high, morels will stop fruiting. In most years, the smaller, early morels arrive right on time, but the really giant golds do not grow unless the moisture continues and the soil temperature stays down. Look for gold morels in riparian areas before the cottonwoods have leafed out and when the tulips are just opening in Denver. I SHOULD wait four to seven days after rain to go looking, but usually can\rquote t stand the suspense and rush right out the minute the rain stops falling.

Boletus edulis also doesn't care much about winter snow but isn't as fussy about soil temperature. In most years, there will be two flushes of Boletes. First, the "Creek" Boletes appear in late June and early July along rushing creek banks where the misty water has created a mini-climate and there is still so me moisture in the soil from the winter snow. Then the second and much larger flush happens in August in response to late July rain. For Boletes, moisture seems to be more important for fruiting than temperature, meaning that high temperatures only cause them to come up faster and doesn't affect the fruiting. If the weather is cool, they may come in five to seven days after rain. If the weather is warm, say 70 degrees or more at 8200 feet, they can come up in as little as three days. So, when you are deciding when to go, keep an eye on the rainfall patterns and the temperatures in great mushroom areas such as Fraser for Winter Park, Idaho Springs for Squaw Pass, and Frisco for Shrine Pass. With continued warmth and moisture, Boletes will keep on fruiting for an extended period of time, four to five weeks in the same area. Extreme cold resulting in very cold or frozen soil, baking heat, or excess dryness will put an end to their fruiting.

My theories about the fruiting patterns of chanterelles and matsutake are in their infancy, but I suspect that chanterelles require cool, but not-too-moist conditions while matsutake wait for moist and warm days. Last year's matsutake crop in Colorado rivaled that of the Pacific Northwest, but the chanterelles were disappointing as they have been for the last three years. I have also been curious about the effect of daylength on mushroom fruiting patterns, but have found no information on this subject. It seems logical to assume that mushrooms can be affected as much as plants are.

So, does winter snow make mushrooms grow? Who knows, but probably not. So far this year, the question has been academic, but I can now safely predict that until the weather cools down and the monsoon arrives, there will be very few mushrooms in Colorado. (Editor's note: This article was written before Colorado\rquote s recent rains.)

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