A host of factors influences the growth of mushrooms, and the exact reasons for their sudden appearance remain only partly known. Certainly the temperature is the most important factor. Mushrooms cannot grow at temperatures below the freezing point or above 40 degrees C. The second most important factor is humidity. Since water constitutes about 90 per cent of a mushroom, it needs a high level of humidity to flourish. That's why mushrooms are so abundant in rainy periods.
In southern Québec, the mushroom season stretches generally from mid-April to the end of October. In spring, only about 100 species can be found, including Mycenas and Ink caps. In a rainy summer, many species appear toward the middle of July, especially Boletes, Russulas and Amanitas. Many summer species appear only in hot and humid weather, and in a dry summer will just skip their turn and come out the following year.
Fall species reach their peak about mid-September. That's the bumper period: numerous can be found, including Milk caps, Cortinarii, Tricholomas and many others. The first frost puts an end to the mycological season, exept for a few tardy species.
It's as important to know the right place to look for mushrooms as it is to know the right time. One should know, for example, that at the beginning of the season, from mid-April to mid-May, very few species can be found in dense forests. They can be found instead at the edges of woods, under poplars and pines, in sandy soil. At that time of year, the mushrooms are mainly saprophytic. Later in the season, from mid-July to mid-August, the best hunting grounds are leafy forests where oak, beech and hickory predominate: many mycorrhizal species may be found there. Finally, in September mushrooms abound almost everywhere, in dense forests and open spaces: but the greatest yield is under evergreen trees, and especially spruce.