November 04, 2020 4 min read 0 Comments

This article is included in our brand new microgreen resource page.

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What Does Mold Look Like on Microgreens?

"Mold or root hairs?" has to be one of the most common questions new growers have when growing their first tray of microgreens.  There are, however, some distinct differences.

Root hairs are thin, featherlike cilia that grow out from the roots to increase the surface area of the new seedling to help with nutrient uptake. They will not have an odor and will only appear around the root of the sprout.

Mold on Microgreens

Mold, often appearing as spider-web like strands, can overtake a tray of microgreens when given the right conditions. Mold and fungi thrive without proper drainage, air circulation, and lighting.

Here are some key things to look for: 

  • offensive odor
  • grows above soil and directly on greens
  • slimy to the touch
  • will not disappear with rinsing
  • can appear as black, purple, blue spots on leaves

Trays can also fall flat due to mold, also referred to as damping-off.    

 Damping-off in Microgreens

When plants are not receiving proper airflow, soil-based fungi can cause a condition called damping-off. The wet microgreens create an anaerobic environment which usually results in the loss of the tray.

The mold begins to steal all of the nutrients from the microgreens and they fall at the base.  The fungi attack both the root and the stem. 

Top 10 Ways to Prevent Mold on Microgreens

1.  Plant in trays with drainage holes                                                   

2.  Use clean growing mediums that allow for drainage                     

3.  Control the humidity of your grow space

4.  Provide trays with proper air circulation with the use of fans

5.  Set up proper lighting conditions allowing for 6-10 hrs. daily

6.  Presoak and disinfect "dirty" seed varieties

7.  Avoid seeding too densely 

8.  Properly disinfect trays between plantings

9.  Disinfect flood trays regularly with H202 

10. Use the bottom watering method for microgreens

What Causes Mold in Microgreens? 

Mold and fungi multiply quickly if given the opportunity. Many times poor drainage is the culprit. Microgreens need frequent waterings to grow, but pooling moisture left on the bottom of containers are often breeding grounds for mold.

We recommend microgreen growing trays with holes to prevent this issue.

The same type of moisture collection can also occur if you are using a growing media that does not encourage efficient drainage.  We find that potting soils that include a good ratio of peat moss and perlite promote better air circulation and drainage. 

Learn more about growing mediumsBeginners Guide to Soil Mixes, Media, Amendments and Fertility

Moisture in the environment can also contribute to mold. The humidity level of your growing space should ideally be between 40-60 percent. Adding a dehumidifier to the space can help to regulate humidity levels.

Lack of proper lighting can also agitate the problem. Mold prefers warm and dark. A full spectrum light provides adequate lighting for the plants and disrupts the mold's life cycle.

Mold prefers stagnant air for breeding and multiplying. Installing proper air circulation is key. We recommend setting up circulation fans in your grow space.

Disinfecting Seeds

Many seed varieties require a pre-soak before planting.  t is a good idea to add H202 to the water during soaking. This can help prevent seed-borne diseases that could result in tray loss. Some seeds are notorious for being "dirty" seeds. 

A few varieties that benefit from sanitation are: sunflowers, cilantro, and peas. 

(Related:  Microgreens & Soaking Seeds- When & Why)

Seed Density for Microgreens

If seeds are planted too densely they are not able to breathe and drain.  The roots will mat up as they grow too closely, preventing efficient drainage. As the tray grows, it often becomes too thick to circulate air through.  This creates the perfect mold growing conditions. 

Seeds vary in weight and size depending on the type. Many growers determine seeding rate by measuring out the weight of the seeds.  This helps to keep the planting density consistent. 

We have compiled a guide, The Ultimate Microgreen Cheat Sheet, with many of the most common varieties and their recommended seeding rates in ounces.

Keep it Clean- Preventing Mold

When it comes to prevention, keeping a clean growing space and equipment is always best practice. We recommend frequent cleaning of grow racks, harvesting equipment, trays. Trays can be scrubbed with a basic soap, followed by a misting of diluted H202 water. 

It is best to allow the trays to thoroughly dry before stacking for storage.

(Related- How to Wash and Care for Seedling Trays)

Bottom-watering Microgreen Trays

Watering microgreens from the bottom ensures a more even coverage for the tray.  Water isn't able to oversaturate areas of the tray causing mold and rot. This also prevents damage to delicate microgreens that can occur during top-watering.

(Related-  Watering Microgreens- Which Method is Best?)

Photo Credit:  @floridamicrogreens

How Do You Remove Mold From Microgreens?

Not every tray is salvageable. Consuming microgreens with mold is not recommended. Even if a tray is only partially covered with mold, spores could be present throughout the tray. Some growers will use 33% food grade H202 (in a spray bottle diluted to 3%) or grapeseed oil to mitigate light mold. 

In our opinion, it isn't worth the risk.

We believe the focus should be on prevention.  Do that, and your likelihood of success goes way up.