What is the white growth found in the seedling soil and is it safe to plant in my garden?


I am a new gardener. I started all my garden plants indoors this year, from seed (about 3-400) and recently, a silvery white fungus or mold is appearing on the soil and spreading to the soil of all my starts. At times it looks like silver threads and other times just a lite silver hue. I have no idea what it is. I’m not sure if it will be safe to put these starts in my garden. And I’m not sure if it will hurt my plants or how to treat it. I’m have included several photos. I don’t want to introduce something dangerous into my garden soil. Could this possibly be a good thing? Is it Mycorrhizal Fungi?


Jonathan Foster, Home Horticulture Outreach Professional

Welcome to the world of gardening and seed starting.

The silvery growth you’re seeing on the soil surface is a common occurrence when seed starting and is typically an indicator of overly wet growing medium. In an of itself, it’s not necessarily a problem, but it does mean your seedlings are at risk for damping off. Your photos look reasonably healthy, so for now, I would adjust your watering regimen to let them dry out a bit more before watering, try to promote good air movement near the seedlings (e.g., space the trays out, place a fan nearby), and transplant them out into the garden as soon as it’s feasible. You can find good timetables for seed starting and seedling transplanting here and here . If you notice signs of damping off, it’s (tragically) often best to pull and destroy the seedlings, as they will not recover.

For next season, I recommend using a sterile, soil-less medium, watering judiciously, and setting up a fan nearby early on in order to promote good air circulation–all elements that will combat the conditions fungi rely on to grow. You can read more seed starting advice in our UMaine Cooperative Extension Bulletin #2751, Starting Seeds at Home.

Happy gardening.