Microgreens & Wheatgrass: Control the Moisture, Control the Mold

By Jordan Freytag

Updated July 5, 2023

Growing Microgreens and Wheatgrass can be some of the most rewarding small-scale gardening because your crop is done so quickly—and frankly, because it tastes so good! However, since growing Wheatgrass and Microgreens require a substantial amount of moisture, mold growth becomes a common occurrence. This causes many folks to become frustrated and even quit, unknown to them the simple steps that one can take to treat and prevent mold. It may sound easier than you think: control the moisture, control the mold.

Mold spores are everywhere! Even though we can’t see them, they are constantly wafting through the air—even as you read this. There is no way to “get rid” of mold spores. But no worries! Mold spores themselves are not inherently bad unless they find the ideal conditions to grow.

Not all mold spores are the same, either. Some grow on wood, food, carpet, and other various places. It is when the spores land on a damp surface to their liking and are exposed to continual humidity that they grow into the familiar spider web-like growth. It is also not uncommon to mistake the micro hairs attached to the roots as mold, but they are actually signs of healthy growth. Understanding this and the role moisture plays in getting mold spores started will give you all the knowledge on how to keep mold spores under control.

Healthy Root Hair Growth

Steps to Control Mold Growth on Microgreens

1. Know your climate. Is it dry? Or is it humid? Sometimes you may need to adjust your care slightly based on where you live and whether you are using soil methods or hydroponic methods of growing. For example, higher humidity areas will absolutely require ventilation or a substantial amount of airflow. Whereas in dry climates, you may get away with less airflow. But, in dry climates, watering may be required more frequently rather than in humid areas. Basically, the trick is to judge what your tray needs based on what the soil or hydroponic growth pad looks and feels like.
2. Check your growing medium. Your soil or hydroponic pad should be moist, not soggy! Gently press your finger into it. Whether it is a pad or soil, the goal is to provide just what the plants need. Not too little or too much, but just right. When checking your soil or pad, it should be spongy—not muddy. You should be able to feel the moisture within the hydroponic pad or soil. It should not be secreted out. Water should not collect on the surface of your tray; it is the ideal environment for mold spores to land and spread. To avoid surface saturation, try bottom watering.

• How to Bottom Water: After your seeds have taken root, pour water into the bottom of the tray so the root hairs will soak it up. This will provide essential moisture to your tray without saturating the top. We recommend nestling a tray with holes inside one without holes to make this process a breeze.

3. Keep the air moving. Keeping your air moving and ventilated is of the utmost importance because (a) it keeps the mold spores moving, giving them less of a chance to settle. (b) it helps keep the air from becoming stagnate and developing increased humidity. Open a window nearby during the day, and or keep a fan going on low in your growing space. Without proper airflow, your flat may appear dewy or give off a pungent scent.

How to Get Rid of Mold on Microgreens

If you find that your trays have already started growing mold, don’t panic. Just try all of the above tips to control the humidity and airflow of your growing space. Then, mix either a few drops of hydrogen peroxide or grapefruit extract into a spray bottle and mist your flat.

• Hydrogen Peroxide Mold Treatment: Mix about 2 Tablespoons of Hydrogen Peroxide with 1 liter of water. Spray over your sprouting microgreens at the first sight of mold. If covering for a blackout period, be sure to check for mold as the dark and wet environment of newly planted seeds during a blackout period are ideal for mold growth to start developing. Early treatment will save your microgreen or wheatgrass crop.
• Grapefruit Extract Treatment: Mix up to 5-10 drops with a cup of water. Spray the affected area.

Soil may be a better option for high-humidity areas because it acts as a great regulator. Hydroponic pads tend to need more care as they don’t hold water as well as soil. So, try both and see which medium suits you and your growing style best!