After the rain: is a mushroom explosion coming, and what does it mean for your logs?

Anyone who has been in the woods over the past few days may already have seen it: after the first proper rain of late August, mushrooms are suddenly back. Dutch mycological researchers and the Netherlands Mycological Society wrote on 30 August that hopes are growing for a genuine mushroom explosion, after a summer in which the underground mycelium in soil, litter and wood was heavily stressed by drought. We are watching with the same suspense, because what applies to the forest applies to the logs in your garden. Here is what is happening now, and how to respond.

Why does rain after drought cause such an outburst?

Because mycelium does not die during drought, it waits, and builds reserves in the meantime. A fungus can stay in standby for weeks without water, and as soon as the wood or soil becomes moist again, two signals arrive at once: there is water, and the temperature is dropping. That is exactly the combination that makes a mushroom fruit. The mycologists point to something else too: plants under drought stress release compounds that actually increase fungal activity in the soil. Cooperation between trees and fungi is crucial in such a situation, and that can amplify the recovery after rain. At the nursery we see the same principle in miniature; it is the cold shower we give a grow kit to force a new flush. Nature is now doing it on a national scale.

Explosion or silence: it could still go either way

The mycologists are honest about it: it could be a mass appearance, or precisely the absence of one. That depends on how deeply the mycelium was damaged and on the coming weeks. A shower after months of drought does not reach into the wood straight away; it is the sum of rain, cooler nights and time that counts. If the next two weeks turn wet and mild, September will probably be one of the better mushroom months in years, precisely because everything wakes up at once. If it stays dry, the surge shifts to October or fails to appear. That is the suspense of this autumn, and the reason every mycologist in the country is walking into the woods every morning these weeks.

What does this mean for your logs?

The same, if you give the mycelium inside them the chance. A colonised log that survived the summer, see the piece on the summer, now gets the signal from the rain to fruit. But a bone-dry log does not absorb enough from a few showers to get going. Help it: give logs that feel light a night in water now, put them back in the shade, and watch the cut ends over the next two weeks. If white patches appear there, your log is joining in with the forest. Oyster mushrooms come first, often within two weeks of the turn; shiitake and the clustering species follow in October when the nights get colder.

And the wood chip beds?

A wine cap bed responds faster than anything. A bed that stalled in July but did not dry to dust can bud again within a week of the rain. Give it an extra watering can and a layer of fresh chips, and check every morning, because wine cap goes from button to oversized in three days, and the slugs are back after the rain too.

September is the month to start

Also for anyone who does not have a log yet. The nights are getting cooler, the air more humid, and that is the best time to start an indoor grow kit again after the summer break. Anyone who kept the cold-loving kits in the fridge, as we recommended in the summer piece, takes them out now: shiitake, lion's mane and maitake want exactly this weather. Outdoors it is the month for looking, not inoculating; that comes in February. But anyone wanting to arrange wood during pruning season can start asking around now, see where to find logs.

26 September: European Mushroom Day

Saturday 26 September is European Mushroom Day, with excursions and activities around fungi across the continent. If the surge holds, it will be a day when the woods show more than they have in years. Join an excursion by a local mycological group and take the knowledge home: anyone who learns in the forest how an oyster mushroom grows on a dead beech looks differently at the log in their own garden afterwards. And anyone who prefers to stay home can make a spore print that day from the first harvest of the season.

We will keep track of what the logs at the nursery do over the coming weeks, and we would love to hear what yours do. Send a photo when things get going. If it turns into an explosion, this is the year to have been there.