You must have come across the term blackout period while reading articles about growing microgreens. Perhaps you have read the term in seed catalogs or product listings in online stores.
Blackout period is a vague term in that it’s talked about in passing but never fully explained. Many authors assume their readers are well-versed about it, not elaborating on it.
The microgreen blackout period is a phase in which trays of microgreens are either loaded or enclosed to prohibit light from reaching the seeds.
What Purpose Does the Blackout Period Serve?
The blackout period can be likened to placing soil over the top of your microgreen seeds the way you’d normally do when planting in a garden outside. There are a number of reasons soil, including soilless potting mixes, isn’t used as a covering for microgreen seeds. You can find the major reasons listed below:
- The seeds are sown so compactly that the developing leaves would “throw” soil everywhere when they germinate. This results in a reduction of soil support for the plants.
- The soil surrounding the young plants would increase the probability of fungal growth and disease.
- Soil would remain on the compactly growing plants, leading to a dirty crop.
- Following germination, the cover soil would be loose. Harvesting would become messy and dirty as a result.
The blackout equipment and methods that we use on newly planted microgreen seeds have supplementary purposes during the growing process. These purposes will be elaborated upon in the remainder of this article.
Materials for the Microgreen Blackout Period
When it comes to blackout materials, there are a lot of options available for you.
You can make use of the lid that came with the planting tray as the foundation. What this does is that is assists in keeping all of the seeds in contact with the planting medium.
If the configuration at the bottom is the same size as the top of the tray, you can also utilize a spare planting tray.
Yes, we do need to allow a period to keep the microgreen tray in the dark. Most tray lids allow light to penetrate or reach the seeds along the edges. To solve this, you can use tea towels to exclude all the light. Alternatively, you can cover the tray lids with a cardboard cutout to block out the light.
Using a dark plastic planting tray with similar sized top and bottoms work great. However, many of those types of trays are large, like ten by twenty inches, that is usually too large for use at homes. A smaller tray typically has a narrower bottom than the top. It is for this reason you should use the lid on top of the seeds and soil.
Is the Blackout Period Necessary?
This question is one that many microgreen growers have in their minds. The blackout period is extremely beneficial for optimal growth and germination, especially when considering radishes. You must have read that some microgreens, for instance, basil, don’t need a blackout period.
Dual Meaning for Microgreen Blackout Period
It is little-known that the blackout period is a bit more than keeping the seeds away from light. When planting more than one microgreen tray, you should stack them on top of each other, placing a weight of some kind on the stack.
Most microgreen seeds love the weight on top of them for the following reasons:
Apart from holding the blackout material on the trays, the weight also assists in keeping the seeds in constant contact with the moist planting media.
Moreover, the weight forces the tiny seedling to better anchor itself in the soil, resulting in a stronger and better-rooted plant.
If you are worried that the plants are not strong enough to deal with the weight, they can easily do it. There are weeds that may grow up through the asphalt. The plants may even shift the weight if left long enough.
The Length of the Blackout Period
There isn’t one correct answer to this. The microgreen blackout period can last as long as it is required for the seeds to germinate, root deeply, and mature to the point that they’re ready to commence photosynthesis. The variables you need to consider include:
- the variety of microgreens;
- air and soil temperature;
- and moisture level
Generally, you should check the seeds after forty-eight hours to observe how well they have germinated, and to gauge their stage of growth.
For some varieties, including radishes, turnips, mustards, broccoli, and kohlrabi, forty-eight is sufficient. For some other types such as borage, cilantro, celery, the blackout period may continue for four to six days.
Further Reasons for Covering Microgreen Trays
There are several reasons we use a blackout period when planting microgreens.
A plastic lid or tray bottom is utilized to keep the microgreen seeds in constant contact with the moist planting media.
The plastic lid or tray also assists in maintaining even pressure over the seeds and tray when the weight is added to the top of the tray.
When the weight is added to the tray, it forces the seeds to grow stronger and root deeper after they germinate.
The weight also ensures that the planting surface is compacted during and after germination; this process reduces loose soil during the harvest.
The Timestamps of the Microgreen Blackout Period
There are far too many variables to give a definite answer, but remember to check the seeds after forty-eight-hour to observe their condition.
You can place some varieties in the light following forty-eight hours. Other varieties may take a few more days in the blackout.
Typically, the seedlings should be pushing the top off the tray. Don’t be concerned if the microgreens appear yellowish or white because they will green up as soon as they are under the lights.
Now that you are equipped with the necessary tools and knowledge regarding the blackout period be mindful of this guide while growing microgreens.