Microgreens are young seedlings that provide a nutritious food source. Growing these sprouts at home is rewarding, but growers often encounter white, fuzzy growth. This growth can be either harmless root development or problematic mold. Mold, a type of fungus, thrives in the warm, stagnant, and humid conditions common in early microgreen cultivation, leading to “damping off.” Understanding how to identify this fuzz and implementing environmental controls is key to a successful harvest. This guide provides steps for identifying, treating, and preventing fungal outbreaks.
Distinguishing Mold from Root Hairs
The most common mistake new growers make is confusing beneficial root hairs with detrimental mold. Root hairs are naturally occurring, fine, white extensions that grow from the developing root to increase surface area for water and nutrient absorption. They appear shortly after germination, typically around the base of the stem or the root radicle, and look uniform and straight.
Mold is a fungus that often presents as a loose, cobweb-like, or cottony fuzz that can be grayish, bluish, or greenish. Unlike root hairs, mold is less uniform, growing in chaotic, patchy clumps across the soil surface. It sometimes climbs the stems and seed hulls.
A simple spray test confirms the identity of the growth: lightly mist the affected area with water. If the fuzz immediately collapses or disappears, it is a harmless root hair. If the fuzz remains standing or appears slimy, it is mold, and the tray should be addressed immediately.
Immediate Steps for Contaminated Trays
If testing confirms the presence of mold, immediately isolate the affected tray to prevent spores from spreading to healthy crops. Heavily contaminated microgreens, especially those with dark, widespread, or musty-smelling mold, should be discarded entirely, as they are not safe for consumption. For small, localized patches of mold, spot-treatment can be attempted to save the remaining crop.
A diluted solution of food-grade hydrogen peroxide can be used as a targeted spray treatment on the moldy area. A gentle ratio is 10 to 15 milliliters of 3% hydrogen peroxide mixed with 1 liter of water, applied directly to the mold. Hydrogen peroxide rapidly oxidizes the fungal spores. After spot-treating, immediately increase air movement over the tray to dry the surface. Stop all top-watering or misting until the surface of the growing medium is completely dry.
Comprehensive Prevention: Controlling the Growing Environment
Preventing mold requires controlling the environmental factors fungi need to thrive: moisture, warmth, and stagnant air. The most effective action is ensuring robust air circulation throughout the growing area. Stagnant, humid air pockets near the soil surface are a primary driver of mold growth.
Placing a small fan to gently move air across the microgreen canopy prevents moisture from settling and inhibits spore germination. The fan should not blow forcefully onto the plants, but create a light, continuous breeze to exchange the air around the trays. Controlling the moisture level within the growing medium is equally important, starting with the watering technique.
Transitioning to bottom watering prevents mold by keeping the stems and leaves dry. Instead of watering from above, place trays with drainage holes into a shallow reservoir of water. This allows the substrate to wick up moisture from the bottom. This technique ensures the roots are hydrated while minimizing surface humidity. Proper drainage holes are essential to ensure excess water does not pool and create a saturated environment.
Substrate and seed hygiene also play a major role in prevention, as spores can be introduced on contaminated materials. Always use a sterile, professional growing medium, as garden soil often contains fungal spores and pathogens. Over-seeding must be avoided, as dense planting restricts airflow between the seedlings, trapping moisture and creating the ideal microclimate for mold.
For seeds susceptible to mold, such as those requiring soaking, a pre-treatment protocol significantly reduces the risk. Soaking seeds for 10 to 15 minutes in a diluted solution of food-grade hydrogen peroxide eliminates surface fungal spores. After soaking, rinse the seeds with clean water before sowing. Maintaining a strict cleanliness protocol is essential. This involves sterilizing all trays and tools between uses with a diluted bleach, vinegar, or hydrogen peroxide solution to kill lingering spores.