Rain, drought and heat: how the weather affects your mushroom logs

An inoculated log asks for little, but it asks at moments you do not always expect. Not in winter, when everyone assumes the frost will finish it off, but in June and July, when it has not rained for three weeks and nobody is thinking about the logs. This piece walks through the weather the way a log experiences it, and says for each situation whether you need to act.

Drought: the only real danger

Mycelium is mostly water and only works in moist wood. If a log's moisture content drops too far, growth stops first, and then the mycelium dies back from the outside in. The first year after inoculation is the most vulnerable period, because the mycelium still sits just under the bark, exactly where the log dries fastest. A log lying in the shade with one side touching the ground holds out for weeks in normal weather. A log standing upright in the sun is in trouble after a week of heatwave.

The rule: if it has not rained for two weeks during the growing season, water the logs. Not a splash, but an hour under a dripping hose or a night in a tub. A log absorbs moisture slowly, and a quick watering can mostly runs off. If you have many logs, lay a soaker hose over the pile and leave it on for an evening.

Heat: worse than drought alone

In a heatwave two things combine: the wood dries and the temperature in the bark rises to levels where most cultivated species shut down. Above thirty degrees in the wood even an oyster mushroom goes into standby, and shiitake genuinely dislikes it. The remedy is shade and mass. Logs lying against each other keep each other cool, logs half under a layer of leaves or wood chips even better. A single log on a patio slab in the sun is the worst spot there is. Move it, temporarily if need be, to the north side.

Rain: almost always good news

A wet week is to a log what a warm shower is to you. Rain refills the wood, lowers the temperature and often triggers a flush on a colonised log. After a proper rainy spell in September or October it pays to walk past the logs daily: that is when the oyster mushrooms and shiitake appear. The only downside of rain is that slugs like it too, and they get there before you do. See our piece on protecting the harvest.

Too wet hardly exists for a log lying freely, by the way. A log sitting permanently in a puddle or in waterlogged soil can rot from below, but that is a matter of placement, not weather. Lay logs on a few thin branches or stones and the water drains away.

Frost: let it come

This is what people worry about most, and it is the least necessary. Mycelium in a log survives a north-west European winter without difficulty, even at minus ten. It pauses growth and picks up in spring where it left off. The only thing frost can damage is mushrooms that were mid-growth when it struck; those freeze and turn soft. So harvest whatever is standing when hard frost is forecast. The exception is velvet shank, which ignores frost entirely and keeps growing.

Wind: the silent dryer

Wind is often forgotten, yet a log in an open, windy spot dries twice as fast as the same log in shelter. That is why we always place logs behind a fence, hedge or dead hedge, and never in the middle of a lawn. If you have no shelter, screen a pile of logs on the windward side with a few planks or a roll of reed matting. It does not have to be pretty.

The calendar in weather terms

Spring: keep moist during the first dry spell after inoculation. Summer: water after two dry weeks, shade in heat. Autumn: do nothing, but check daily after rain. Winter: do nothing, only harvest young mushrooms before hard frost. Stick to that and the weather helps you more than it hinders.