Most mushroom growing kits fruit best between 14 and 21°C, so a hot summer or a warm home can make this tricky. A hot growing environment can stall pinning, dry out the compost, and push your kit out of its comfort zone.
It is important to respect the temperature guidelines of each variety of mushroom growing kit we sell, whilst we can mitigate the affects of warm room, the best starting point is always to choose a variety suitable for your intended environment.

Pick a heat-tolerant species such as Summer Oyster, Pink Oyster, or Reishi, open windows overnight to drop the core temperature of the room, and during peak heat, move the kit into the fridge for a few hours to bring its internal temperature back down.

Why Heat Is the Number One Summer Problem

Mushrooms are not like vegetables. They do not enjoy long sunny days and warm afternoons. Most species you can grow at home evolved in shaded woodland or on cool, damp logs, so the temperature range that triggers fruiting is narrow and sits well below typical summer room temperatures in an insulated UK home.

There is a second problem that is easy to overlook. The compost block inside your kit is not inert. The mycelium is alive and metabolising, and that activity generates its own heat. A grow kit sat in a 23°C room can easily have a core temperature of 25 or 26°C, which is enough to stop pinning, encourage contamination, and cause early flushes to abort. You will find kits wait until conditions are suitable for pinning 

This is why we add temperature disclaimers to listings for heat-sensitive varieties and periods of high heat. If your house genuinely runs hot in summer, the kindest thing you can do for a mushroom growing kit is to wait until autumn. Due to heat you will find our range available fluctuates throughout the year, in summer we will have more pink oyster and summer oyster kits where as winter we will have cool favouring kits such as Enoki.

The Exothermic Compost Problem

A grow kit's core temperature is always warmer than the room it sits in.

Practically, this means you should treat the room temperature as a floor, not a ceiling. If the thermometer on your kitchen wall reads 22°C, assume the inside of the kit is closer to 25°C. Plan your cooling around that reality.

How to Cool a Grow Kit in Hot Weather

1. Open windows overnight

British summer nights usually drop several degrees below daytime peaks, even during a heatwave. Opening windows after sunset and leaving them open until early morning is the single most effective free cooling tool you have. It pulls the core temperature of the room down, and that drop is then absorbed by the compost block, giving the kit a cooler starting point for the day ahead.

If you can run a cross-breeze through two opposing windows, even better. This also helps with fresh air exchange, which mushrooms need in order to form proper fruiting bodies rather than long, leggy stemsm just be mindful of draughts.

2. Move the kit out of direct sun

A windowsill that catches afternoon sun can hit 30°C or more even when the rest of the room is comfortable. Move kits to a north-facing surface, an internal hallway, a tiled bathroom, or the floor of a cool cupboard with the door cracked open. Tiled and stone floors hold cool overnight and release that coolness slowly through the day. For more on choosing the right spot, see our guides on where to place your mushroom kit and where not to place it.

3. Use the fridge during peak heat

During a serious heatwave, the fridge is a legitimate tool. Placing a kit in the fridge for two to four hours during the hottest part of the afternoon brings the core temperature back down without harming the mycelium. This is particularly useful if the kit has already pinned, because pins are the most heat-sensitive stage of the whole grow.

4. Mist more often, in the cool of the day

Hot air is drying air. In summer you may need to mist twice or three times daily rather than the usual two, but always do it in the cool morning and evening rather than the middle of the day. Misting in midday heat can create a humid, warm pocket inside the bag that encourages bacterial blotch and contamination. For the full method, see our misting guide. Over watering is still possible and watering on the caps can be a bigger issue for evaporation, in high heat environments if you are spraying the caps, the evaporation itself is very drying.

Best Mushroom Varieties for Hot Homes

Not every mushroom struggles in summer. Some species are genuinely well suited to warmer indoor conditions, and choosing the right variety is the easiest fix of all.

Varieties to Avoid in a Hot Home

A few species really do prefer cooler conditions, and trying to push them through a heatwave usually ends in disappointment. Lion's Mane needs to stay below 20°C and is particularly prone to drying out and going pink at the tips when stressed by heat. Enoki prefers 10 to 18°C and is genuinely a winter-and-shoulder-season kit. 

If you have one of these kits and a heatwave hits, is to either delay the starting of the kit by a week in the fridge, or if already growing to make use of a few hours a day in the fridge to lower the core temperature.

When to Wait Until Autumn

There is no shame in delaying the purchase. If your home routinely sits above 24°C during the day in summer and the nights are not cool enough to bring it down, your results are likely not going to be as good as you would wish, through no fault of your own. You will get a small flush, lots of stress signs, and possibly contamination.

A Realistic Summer Routine

If you are growing through July and August in a typical British home, a workable daily rhythm looks something like this. First thing in the morning, before the day heats up, mist the kit thoroughly and check the pins. Ensure the kit is in the coolest spot in the house for the afternoon, ideally a tiled floor or a north-facing surface. If the room climbs above 23°C in the afternoon, give the kit a two-hour holiday in the fridge. Mist again in the evening as the temperature drops, and open windows overnight to reset the room temperature for the following day.

Done consistently, this routine will get you through all but the most extreme heatwaves, and it works particularly well with Summer Oyster and Pink Oyster.

Frequently Asked Questions

Published by Merryhill Mushrooms, a six-generation family mushroom growing business in Storrington, West Sussex.