How to Kill White Fuzzy Mold on Seedlings

Kill Seedling Mold in Your Garden

Mold and Mildew on Dahlia Leaves
Nancybelle Gonzaga Villarroya / Getty Images

I've gotten a few questions over the past week or two from readers who have noticed white, fuzzy mold growing on their seedlings. This is a fairly common issue for those who start their own plants from seeds. Most of us plant our seeds and take care to keep the seedlings moist, but that can cause the white fuzzy mold to appear on them.

There is good news for your seedlings--and your garden, too. The fungus itself is not going to hurt  your seedlings.

The bad news: that fungus is a sign that your soil is too wet. Soil that is too wet can result in having the delicate roots of your seedlings rot, which will eventually result in plant death.

How to Stop White Fuzzy Mold on Seedlings

Luckily, the mold is an easy thing to fix. Chances are, you are causing the mold by watering too much. Don't water your plants-to-be unless the seedlings really need it. It is easy to get into a routine of just giving them a quick water every day or so "just to be sure," but this can sometimes do more harm than good. Check the soil's moisture with your finger; only water if the soil is dry. That simple check can help you stop the white fuzzy mold from growing. 

Rethink how much you water when you do water. You may simply need to cut down the amount of water you put on each seedling--another way to reduce white fuzzy mold for healthier seedlings.

Another thing that can help kill off the mold and prevent it from growing is to increase the air flow around your seedlings.

You can do this by having a fan running nearby for at least a few hours a day. Not only does this help prohibit fungal growth, but it also results in sturdier seedlings.

Additionally, you may want to look at how much light the seedlings are getting. They need at least twelve hours of good, strong light per day to grow well.

That also helps the water to dissipate and not sit stagnant. Try not to place them in direct sunlight, either, because covered trays can get too hot and damage the seedlings. Check the temperature, too. The best photosynthesis occurs when the temperature stays between 77°F and 82°F).

Finally, if at all possible, consider a system that lets you water from the bottom of the seedling container. This not only encourages the roots to grow deeper. It also helps alleviate mold and fungus because the surface of the soil is not constantly moist, so it cannot grow.

Once you do one or all of those things, you can actually remove the white mold from your seedlings. Gently scrape it away with a knife or spoon.