Microgreens, Mold & More

Microgreens love warmth and moisture; unfortunately so does mold. Whenever you have any growth medium holding water in a warm & humid environment, you risk the chance of also growing mold … but there are many tips & tricks to reduce the occurrence of mold on your grow mats.


Where does mold come from? 

Mold grows on microgreens, just like mold grows in any other environment. Mold requires moisture, warmth, lack of air flow, and bacteria to flourish and grow. 


Does mold affect microgreens?

Yes. If there is mold on your microgreens, they will not be safe to eat even though they may continue to grow as per usual. Discard your moldy crop and your growing medium as the mold spores will live on and very likely affect your next crop. 



How do I prevent mold on microgreens?

Thankfully, there are many things you can do to help prevent mold from forming on your crop:



Before you start growing, soaking your seeds or preparing your trays – it is very important to clean and sanitize all your equipment & seeds    thoroughly. 


Trays – hot, soapy water will do the trick but to take it one step further, you may choose to use white vinegar or food grade hydrogen peroxide. Either choice should be used very sparingly (about 3% solution with water). Bleach is not recommended but some do use it. 


Seeds – seeds are a common source of mold contamination and they should be thoroughly cleaned & rinsed before growing. Soak your seeds as per package recommendations and add a teaspoon of food grade hydrogen peroxide. Rinse several times when done soaking then proceed with sowing (ensuring to not sow seeds to close together! Follow seed density recommendations). 


Light and Warmth

Mold loves warm & dark not bright & light. You will be starting germination of your crop in the dark; however as soon as germination has occurred you should move your plants into the warm light. If a warm spot in direct sunlight isn’t an option, then use a full spectrum grow light.


Proper Air Flow

It is essential to ensure proper ventilation during each step of your grow. Mold doesn’t like moving air, it likes stagnant air. Stagnant air allows mold to multiply and breed; whereas moving air doesn’t allow the bacteria to settle. When you’re starting your seeds, they are generally in the dark and/or covered with a humidity dome – this is a time of high mold risk due to little air flow and dark, damp conditions. Simple fix! Add a couple of ventilation holes to the side of your humidity dome and/or tray and then place a small fan in the area. 


Control the Humidity 

Your microgreen crop needs water to survive, in fact moisture in the growing medium is essential. But darn it, mold loves this moisture too! Invest in a dehumidifier to remove humidity from the air (but make sure your grow tray is well saturated).


I’ve heard root hairs are not mold, what is the difference between root hairs & mold?

Root hairs. Most crops have hairs that form part of the root. These fuzzy little hairs stick out from only the root – this is key difference in determining mold or root hair – and allow your seeds to absorb additional water. 

Mold. Mold often looks like a spider-web spreading all over your crop (not just the root, but everywhere). Mold may also be slimy … it is just gross overall. In rare instances, you may see black mold or other colours. 


I’ve got mold starting, now what do I do? 

There are a few things you can do:

  1. Carefully remove the moldy plant or affected part of the tray. This should remove the problem area and may prevent any more mold from spreading. Unfortunately, mold is not easy to see, especially when just starting to grow, so this may not fix the issue. 
  2. Make a spray bottle with a mixture of water, white vinegar and/or hydrogen peroxide. The ratio should not be more than 80/20 (any stronger and you’ll burn the leaves) and spray this all over your crop. It should kill the mold without harming your crop. 
  3. Direct sunlight.  There is nothing better than a hot, sunny day to kill mold. But remember, the drying effect of the sunlight will also quickly dry out your growth medium. Keep your tray well watered and keep a close eye on your crop.

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