Mold… or root hairs?

You have just uncovered your tray. What is that white stuff in your microgreens? Oh, no! Is it mold??

Chances are, you are seeing root hairs, not mold.

Root hairs are the part of the root system that reaches into the soil to suck in the nutrients and moisture needed for healthy plant growth. They are easy to identify- they grow directly out from the root. When looking from above, your tray may seem like it is filled with white stuff, but when you get closer, you see that the little masses of white each originate from a distinct root. Using a magnifying glass (or take a photo with your phone and blow up the photo) you will have a better idea of what you have in there.

Root hair on radish root — Root hair on radish microgreen

Mold looks like a cottony, webby mess.

Mold originates from the soil or from a bad seed- never from the roots of the seed. It grows in all directions like a Halloween spider web. It normally starts in the middle of the tray but depending on conditions may completely cover the tray.

a description of mold vs root hairs — A visual of mold and root hair in a tray of peas

The easy, definitive test

If you are still not sure whether you have mold or root hairs, the best test is with a spray bottle. Spray water over the area. If it is root hairs, they will seem to disappear completely when wet. Mold will not disappear, but will gather water droplets and lay against the soil and greens.

What do I do if I DO have mold?

If the mold is confined to a small area, carefully scoop out the nasty bit. Spray the area with hydrogen peroxide(H2O2)* to eliminate any mold spores on the soil, then place the tray in an area with bright light and good airflow. The trick is to dry out the top layer of soil as quickly as possible. Always bottom water, especially in areas with high humidity.

Root hairs vs mold on buckwheat microgreens — root hairs on the left mold on the right

If the whole tray is affected…

If the mold is systemic and the whole tray looks bad, be safe and just dump it into the compost and start again. Although you can sometimes harvest above the mold safely, there are some molds that are very unhealthy to consume. It is best to err on the safe side. Don’t worry-you will figure it out! Treat the tray as a valuable learning experience, throw it out, clean it up, and try again.

Here are a couple of tricks to be sure it does not happen again:

Make sure you are using only fresh soil- never reuse soil for microgreens (unless composted thoroughly).
Use coco coir, or a good quality potting mix that drains well.
Start with clean trays and equipment. All of our 5×5 planting trays are dishwasher safe so be sure they are squeaky clean.
Do not moisten the soil too much. If you squeeze a handful and drops come out, it is too wet.
If you have a frequent problem with mold, keep a fan running in the growing room, with plenty of fresh air moving around the room.
Check the humidity in the room- if it is continually over 35%, try running a dehumidifier that is big enough to reduce the humidity to between 30-40%.

*Hydrogen Peroxide is a safe treatment for mold

IMPORTANT: 3% H2O2 is approved and safe for use in organic gardening as it easily breaks down, or decomposes, into water and oxygen gas.

Exposure to mold causes the H2O2 to decompose as it destroys the mold molecules. Exposure to light also causes the decomposition of H2O2. What remains is pure water and air.

Spray moldy areas lightly with regular 3% H2O2 and allow to sit for an hour or so before placing it under bright light. You can also soak the seeds before planting, but if you are continually getting mold, it is best to determine the cause, not just treat the symptom.

When you spray the H2O2 on mold or dirty surfaces, listen carefully- you will hear it bubbling as it interacts with the mold and changes to its gas and water state.