What makes a mushroom season?
By Daniel Butler, author and forager
This is a constant source of debate among foragers as they look forward to the annual autumn bonanza. What will it be like? Will there be lean pickings or a total glut?
Some factors such as temperature and rainfall over the previous months play important roles, but these alone cannot explain everything. As a result, every keen mushroom hunter has their pet ‘extra factor’.
When should I rush to the woods? When has it peaked? When is it over?
(Photo: author’s own)
But let’s start with the things everyone agrees on. Mushrooms have a very high moisture content (usually over 95%), so water availability is critical. Even minor droughts hit mycorrhizal species associated with shallow-rooted hosts badly. Field mushrooms really struggle to fruit in dry conditions and those that do emerge rapidly desiccate in hot weather. Chanterelles also need damp conditions in their woodland habitat. Yields will be poor if the leaf mould and soil are dry and hard.
Temperature is also clearly critical. In spring, as the soil begins to warm, morels and St George’s appear. A month later chicken of the woods erupts from tree trunks. Later, as things begin to cool in autumn, the widest range of fruiting species arrives. The timing of these events is driven mainly by rising or falling mercury.
After this, however, the obvious patterns begin to break down. For a start, despite our obsession with the British weather, in reality climatic conditions vary much less than we imagine. There is a strong element of self-absorption when we talk about weather. Humans might be all too aware of months of cloudy skies, but mycelia are buried beneath soil, bark or leaf mould: light levels and day length should be irrelevant.
Morel’s grow as happily in a Mediterranean Turkish spring as in damp Norfolk
(Photo: author’s own)
Another reason to downplay the relatively mild fluctuations in conditions from one British summer to another is that most of our edible species are found throughout Europe, thriving in conditions which vary from the scorching heat of the Mediterranean to the balmy cool of Scandinavia.
The complications of simply saying it all relies on temperature and rain are illustrated by the extraordinarily dry, hot, summer of 1976. The ‘Drought Year’ should have been a disastrous fungal year, but actually it saw record-breaking porcini yields here in Mid Wales.
Even within individual seasons, it is difficult to predict the emergence of generally abundant species. Yes, heavy rain in summer often prompts a flush of pastoral species and chanterelles, but whether these emerge days or a week later seems random. Similarly, porcini usually first emerge in September, but next they might begin to pop up in July for no discernible reason.
What is bad for humans might be good for mushrooms
(Photo: author’s own)
Thus in 2023 I hit a glut at the beginning of August, but after this promising start, things tailed off. On the other hand, the whole summer saw bumper loads of chanterelles – and yet there was almost no honey fungus in the autumn.
Do lunar cycles really influence mushrooms?
(Photo: author’s own)
Peter Jordan used to claim everything was linked to lunar cycles. Like many theories produced by this loveable raconteur, I think he rattled it out because it was a good story – not that it was based in any genuine science. He may have gleaned the idea from a popular East Anglian saying:
When the moon is at the full,
Mushrooms you may freely pull,
But when the moon is on the wane,
Wait ere you think to pluck again.
I am deeply sceptical and have certainly never having been able to link the emergence of mushrooms to the full moon, on the other hand I know and respect several foragers who share the theory.
My personal belief is that growing conditions for trees drive woodland mushroom fruiting. Their mycelia sheath their hosts’ roots while sending out hyphae to collect nutrients. They pump these into the tree in return for sugars and water.
Porcini harvest sugars and water by plumbing into the deep roots of their host
(Photo: author’s own)
All this means that unlike pastureland species, a cepe or chicken of the woods is plumbed into its host’s deep roots. This insulates them in dry spells. During the famous ‘Drought Year’, the trees produced abundant sugars in the cloudless conditions, but the water shortage meant they struggled to turn these into timber (lignins are much longer carbohydrate chains). The fungi wrapped around their roots harvested the sugars and when rain finally arrived, the timing was perfect for the mycelia to fruit.
Mycelia swathing the roots of a conifer seedling
(Photo: National Geographic)
Well, it sounds plausible, but in the end the truth is that no one really knows what makes mushrooms tick. It’s why we can’t cultivate the overwhelming majority.