What do microgreen farmers mean when they “blackout” their microgreens? Blacking out is the process of depriving your plants of all light. Blacking out is possible at large scales in a dark room. On a smaller scale, farmers will place blackout domes over each tray. If a farmer adds a blackout step, it happens after germination but before using the grow lights.
Why include blackout at all? Plants need light to photosynthesize and survive. Plants can survive for a few days to a few weeks after germination using an internal energy reserve in its seed, called the endosperm. The plant wants to find a light source, regardless of the endosperm. When you deprive a plant of light after germination, it begins to panic. The ensuing process is called etiolation. Etiolation causes the plant to elongate its stem. You can think of it as the plant stretching its stem to “reach” as far as possible to seek out a light source.
Farmers will use a blackout step to stretch the stems, which makes the crop easier to harvest. Longer stems create more space between the lip of the tray and the crop canopy. Adding a blackout step is entirely unnecessary for most crops. Most varieties naturally develop a long enough stem that harvesting shouldn’t be a problem. A few notable exceptions would be basil and arugula. Depending on your preferred grow time for these crops, the short stems can make harvesting difficult. If you’re harvesting by hand, you have flexibility and control. You can angle your knife to reach lower on the stems. You can harvest slower to prevent damage to the crop or canopy. However, if you’re using a mechanized harvester, like the Quick Cut Greens Harvester (QCGH) from Farmers Friend, there’s less margin for error. When using the QCGH for microgreen harvesting, it’s often mounted to a table, which means the blade is fixed in position. You lose the flexibility to angle the blade below the lip of the tray. Also, implicit in using the QCGH is that the whole harvest process is moving much faster. You’re processing 10-50x as many trays per hour. In this context, you don’t want trays with short stems where the harvester is likely to mangle the canopy.
Blacking out is costly. It will cost you extra time, extra steps, extra space, extra equipment, and extra cleaning. It takes more time to take dozens or hundreds of trays from germination and put them into blackout before moving them again to the grow lights. It makes your operation more confusing when you add an extra step into the production process. It requires extra space to store trays while they sit in a blackout. It requires more money to buy blackout domes to cover each tray during a blackout. Don’t forget that you’ll need extra space to store the blackout domes when not in use. Lastly, it requires more labor and time to clean the blackout domes between uses to prevent disease transfer.
I believe we should avoid blacking out at all costs. Blacking out is an unnecessary step in producing microgreens. The costs far outweigh the benefits. If you need slightly longer stems to ease harvesting, try leaving your crops in germination for a day or two longer. Similarly, try putting the trays onto your grow racks, but keep the lights off for an extra day or two.
Caveat: This article is not relevant to crops that require blackout to grow properly. The only microgreen of which I know this is applicable would be popcorn shoots.
Stages of Production - Soak, Plant, Blackout, Humidity Dome, Lights, Harvest, Pack, etc.
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