If you've ever started microgreens, only to see them wither and die soon after germination, you’ve encountered “damping off.” "Damping off" is a common phrase for the affect that certain pathogens have on young plants. Plants suffering from damping off will see their stems wither and rot at the soil line. We’ll discuss what causes damping off, how to mitigate its presence, and what to do if it takes hold.
Definition and Causes
Damping off is a soil-borne fungal disease that affects seedlings, primarily during the germination and early growth stages. It's caused by several pathogens, including Pythium, Rhizoctonia, and Fusarium species. These pathogens thrive in wet, poorly drained, and overcrowded conditions. If these conditions sound familiar, it’s because they perfectly describe a germinating tray of microgreens. The pathogens that cause damping off often enter the farm because they’re dormant, but present, in your grow medium. They can also hitchhike on the surface of your seeds.
Symptoms of Damping Off
The two primary inputs to your farm are soil and seeds. Despite a company’s best efforts to sterilize their soil or test their seeds for pathogens, it’s impossible to consistently provide perfectly sterile inputs. Your best hope as a farmer is to buy seeds and soil from reputable sources. Don’t ever reuse soil. Don’t ever grow seeds that have fallen on the floor.
Cleaning means removing the organic matter, like stems and dirt, from a surface. Sanitizing means to dramatically reduce the presence of pathogens to a level deemed safe for food contact. We use a product called SaniDate 5.0 to sanitize our trays, harvest totes, knives, and table tops. Cleaning must always precede sanitizing. Do not reuse your 1020 trays without first cleaning and sanitizing each one. If damping off is present in the farm, cleaning and sanitizing all tools and trays will help stop it from spreading further.
Do not overwater during the planting step. Remember that damping off usually develops during germination because the conditions are perfect - wet, warm, dark, and without airflow. Your microgreens don’t need that much water to make it through germination because they’re likely stacked with a paver on top. This type of germination setup doesn’t allow for much airflow or evaporation. Water logging the tray during planting will push out all air pockets from the soil, which leads to anaerobic conditions.
Air circulation is good for trays in germination, as well as those growing under lights. You want to create a gentle breeze throughout the farm. You don’t want to blast your germinating trays with non-stop air. Too much airflow will dry out your germinating trays, leading to an even faster death than that caused by damping off.
Keep your germination area between 65-75F or 18-24C. The germination area, if possible, should be a few degrees colder than the rest of the farm.
Unfortunately, there isn’t much hope for your tray if it develops damping off. Your best option for an intervention is to scoop out the soil from the affected area and throw it away. Be sure to remove the affected area plus an extra inch in all directions. Spray the empty area with dilute hydrogen peroxide, Zerotol, or SaniDate. The damping off is likely to continue spreading, which is why prevention is better than intervention.
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