Individual Potted Plants With White Fluffy Fungus On Seed Starting Soil
soil fungus
(Image credit: skurvits via Q&A)

Many people enjoy starting their own seeds. Not only is it enjoyable, but economical as well. Because starting seeds indoors is so popular, many people become frustrated if they run into problems. One of the more common seed starting problems is the development of a white, fluffy fungus (some people may mistake it for a mold) on the top of the seed starting soil that can eventually kill a seedling. Let's take a look at how you can stop this fungus from ruining your indoor seed starting.

How to Stop White Fungus on Soil

The number one reason that white, fluffy fungus grows on your seed starting soil is high humidity. Most seed growing tips will suggest that you keep the humidity high over the soil until the seeds have fully germinated. Your seedling planter probably has a lid or cover that helps with this, or you have covered your indoor seed starting container with plastic. Sometimes this raises the humidity to a level that is too high and encourages the growth of this white, fluffy fungus. Either prop open the lid of the seedling planter about an inch (2.5 cm.) or poke some holes in the plastic over the container you are starting seeds in. This will allow more air circulation and decrease the humidity some around the seed starting soil.

I Reduced Humidity but the Fungus Still Comes Back

If you have taken steps to increase the air circulation around your seedling planter and have decreased the humidity around the seed starting soil and the fungus is still growing, you'll need to take additional steps. Set up a small fan that can blow gently over your indoor seed starting setup. This will help to get the air moving, making it much harder for the fungus to grow. Be careful though, that you keep the fan at very low levels and only run the fan for a few hours each day. If the fan is running too high, this will damage your seedlings. Starting seeds indoors doesn't need to be tricky. Now that you can keep the fungus off your soil, you can grow healthy seedlings for your garden.

Heather Rhoades
Founder of Gardening Know How

Heather Rhoades founded Gardening Know How in 2007. She holds degrees from Cleveland State University and Northern Kentucky University. She is an avid gardener with a passion for community, and is a recipient of the Master Gardeners of Ohio Lifetime Achievement Award.