Fruit Flies, and how to keep them away from your mushroom kit…
Mushroom growing is a joy - watching those first little pins emerge is nothing short of magic, but if you've ever noticed tiny flying visitors around your grow kit, you’re not alone.
Fruit flies and fungus gnats love the same warm, humid environments mushrooms do. Luckily, there are easy ways to prevent them from moving in and while these insects are more of a nuisance than a threat to your mushrooms, no one wants them hanging around.
Prevention is better than cure:
Here are some easy tips to discourage flying pests from setting up camp:
1. Choose the right spot
Place your mushroom kit in a bright, well-ventilated space - but away from fruit bowls, houseplants, compost bins or any other moist organic matter.
Kitchens are a great place to start growing, but if you have a few fruit flies already hanging around, a quiet corner away from these little pests is better than next to your ripening avocados.
2. Don’t overwater
Overwatering doesn’t just upset your mushrooms - it can attract gnats. Stick to 2–3 light mists per day and ensure your kit drains properly.
When watering your kit, keep the outer surface of the bag damp. You don’t need to peel back the plastic or water the substrate directly - pooled water inside the bag creates an inviting home for tiny intruders.
3. Use a mesh cover
If you're in a particularly fly-prone area, covering the open front of your kit loosely with a fine mesh or breathable fabric (like muslin) can help keep insects out, while still allowing airflow.
4. Catch early invaders
If you do spot some flies, a small apple cider vinegar trap (just a shallow cup with a few drops of washing-up liquid) nearby can lure and trap them before they settle in.
5. Old kits can attract new guests
If you’re growing a second or third flush of mushrooms from the same kit, be aware that older mycelium can become more attractive to flies. This is especially true if the kit has been sitting in a humid space for a while. Rest the kit properly between flushes and keep an eye out for signs of mould or decay - they’re a dinner bell for fungus gnats.
What if they’ve already moved in?
If you've noticed a few flies under or around the opening of your grow bag, don’t panic.
Remove any visible flies, give the area a deep clean and reduce moisture levels slightly - you can do this by draining any access water that’s built up inside your kit.
During the milder months, you can move your kit outdoors till your mushrooms are ready to harvest. Choose a sheltered, humid spot that’s out of direct sunlight and not too exposed to wind or temperature swings. Just be sure it’s somewhere you’ll remember it.
A rest period (as described in your second flush instructions) can also help break the cycle.
Mushrooms still thrive!
The good news - a few fruit flies or gnats won’t harm your mushrooms. With the right care, your crop will keep growing strong, and once you’ve harvested, you can rest and refresh your kit to try for a second flush - fly free.
Join the mushroom-growing movement -
Growing mushrooms at home is one of the most rewarding, sustainable and space-friendly ways to engage with food. Little hiccups like fruit flies are totally manageable - and we’re here to help you grow happy, healthy mushrooms all year round.
Ⓒ Caley Brothers 2025
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