1. Water your plants properly. Fungus gnats love to find overly moist soil to lay eggs. Allow your soil to dry 1-2 inches from the top between watering. In young plants this can also help with root development where the roots grow further to reach new water.
2. Use a well aerated soil with perlite or vermiculite. Soils with too much peat or compost can retain moisture longer than needed inviting gnats find a home.
3. Keep air moving across the top of the soil with a fan. This will help dry the top of the soil to discourage adults from laying eggs.
3. Use hydrogen peroxide with your feeding schedule for preventative or as a drench to kill larvae. For bad infestations use a product like Root Cleaner and follow up after the initial application until they are gone. Sticky Traps hung above the pots or soil will help with adults.
Any other tips to share? There are a lot of other options that I didn't mention for organic and hydroponic gardens also. Let us know!
Paul Davis is the owner of Green Dragon Hydroponics, and an avid gardener with over 12 years experience in focused DIY indoor gardening, both soil and hydroponic applications.