Mold on Microgreens

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Mold on Sunflower Microgreens seeds

What is Mold

The purpose of mold is to break down dead matter. Mold is a spider-web like structure that builds up in warm, wet and dark environments. It feels slimy when touched and has a musty smell.


What is damping off

It is the death of young seedlings as a result of a fungal infection encouraged by damp conditions. Damping off typically happens during the first week of germination and can be detected if you see the stems turning brown or mushy.

Is it Mold or root hair?


Certain microgreens like amaranth have root hair on the roots to help uptake the nutrients. The root hair has a hairy fuzzy structure (not spider-web) and it is only on the roots so it is easy to detect if it's mold or just root hair. The mold makes your microgreens smelly (musty smell). The mold will generally be on small patch(es) while root hair will be throughout your tray.


If you are still confused if it is root hair or mold, just spray some water over it. If its root hair, it will disappear after the rinse, and come back in a few hours. If it does not disappear, its mold.

Check out this YouTube short on Mold.

Why mold occurs in microgreens


A combination of following things can build mold and fungi in microgreens:

  • Improper drainage or overwatering
  • Poor air circulation
  • Dark environment
  • High seed density leads to inefficient drainage and poor ventilation that leads to root rot. If the seeds are overlapping, the top seeds start to germinate, and the bottom seeds start to rot.
  • Mold loves humidity. If you have high humidity (more than 50%), the microgreens are going to get damp.

Where does mold grow on Microgreens

Mold grows on seed hulls, stems, or leaves of the microgreens. If it is only on the roots, it's very likely just root hairs and not mold.

How to prevent Mold in microgreens

Follow these steps to prevent mold in your microgreens:

  • Never let the tray become soaking wet. Overwatering leads to excess moisture which creates Mold
  • Water from the top during germination, water from the bottom during vegetation. It prevents mold and rot on foliage and stem.
  • Keep the room temperature between 68–75°F/20–24C° and humidity at 35% to 50%.
  • Use a fan to provide air flow, to keep the spore moving.
  • If you don’t have a fan, use shallow trays instead of deep ones so the base of the plant is closer to the top of the tray. This will encourage air flow across the base of the plant where most of the mold problems typically occur.
  • Use a dehumidifier to keep the humidity in the range of 40 to 60%.
  • Fill the tray with water to test if the drainage holes are not blocked.
  • Try seeding less densely than before.
  • If most of your seeds don’t germinate, that will cause mold as the purpose of mold is to break down dead matter. Use high quality seeds that have details about when the seed was harvested, the germination rate, lot no. (so that it is trackable) if something goes wrong with one batch of seeds.
  • Try using soilless growing medium like a combination of peat moss and perlite that provide better drainage.
  • During the blackout phase of seed development, only mist some water that is enough for germination. Overwatering while keeping the tray in the dark is the ideal condition and the most common time when you could see mold in your microgreens.
  • Weight your seeds before planting so you always keep the same seed density everytime you grow.

What to do when microgreens get mold

Just toss the tray that has been contaminated with mold. Some growers use 33% hydrogen peroxide (in a spray bottle diluted to 3%) or grapeseed oil to mitigate light mold. 


Instead of thinking about saving a molded microgreens crop, it is better to think of what modifications you need to make in your grow space and your seeds to prevent the mold in the first place.


Clean the tray and then disinfect the tray with H2O2 (hydrogen peroxide).


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