Fuzzy white mold is a common issue for seedlings, but the fungus itself does not hurt your growing plants. Fungus, however, is a sign that your soil is too wet. Soil that is too wet can cause the delicate roots of your seedlings to rot, which will eventually result in plant death.
Remove Mold Gently
Once you do one or all of those things, you can remove the white mold from your seedlings. Gently scrape it away with a knife or spoon.
Reduce the Amount of Water You Give Your Plants
Most seedling mold is a result of watering too much. Don't water your plants-to-be unless the seedlings need it. It is easy to get into a routine of just giving them a quick watering 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 before it starts.
Rethink how much you water you add when you do water your seedlings. You may need to cut down on the amount of water you put on each seedling—another way to reduce white fuzzy mold for healthier seedlings.
A second simple way to kill off mold or even prevent it from growing is to increase the airflow around your seedlings. You can do this by having a fan running nearby for at least a few hours a day, or, if your seedlings are in a covered tray, prop the top open to increase airflow. Not only does this help prohibit fungal growth, but it also results in sturdier seedlings.
Take a careful look at how much light the seedlings are getting. Most need many hours of good, strong, indirect light per day to grow well. That also helps the water to dissipate and not sit stagnantly. Avoid direct sunlight, because covered trays can get too hot and damage the seedlings.
Few seedlings will flourish in chilly or hot surroundings. The best photosynthesis occurs when the temperature stays between 77 and 82 F. If you are using a heating mat under your seedlings, turn it down or off to avoid overheating your plants.
Thin or Repot Crowded Seedlings
Most gardeners plant several seeds in the same seedling pot. If you're lucky, all of the seeds will sprout; once they start to really take root, though, they will start to crowd one another. Crowding can lead to fungus. To avoid this problem, simply thin out your plants by plucking out a few from each of your pots. Alternatively, gently remove and repot some of the plants to relieve crowding.
Consider a Bottom-Watering System
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.