Spread enough moist potting mix in an open flat with drainage to fill it about 1 inch full. With your hands or a board, press gently so you have a smooth surface.
For this particular case, measure 2-2.5 tablespoons of Cherry Belle Radish seed*. and with a fluid motion, shake it gently to cover the soil surface uniformly. Gently press down evenly again over the surface to embed your seeds in the soil.
Take paper towels and cover the surface of your flat with a single layer, making sure to get the paper towels into the corners. (This acts as soil would, but has the added benefit of keeping the plants much cleaner, and easier to maintain.) Put the seeded flat into the open flat with no drainage. Water and then cap with a propagation dome, and put them in your seed starting station, preferably on a heat mat.
Monitor your trays closely. When the paper towel starts to get dry spots, it is time to water again. They should germinate in a few days. When they do, remove them from the heat mat, if you are using one.
Once the seeds have started to lift the paper towel up off the surface, and when the towel is moist (but not wet) gently check to see if you can pull the towel off without pulling the plants with it. If they come up too, it isn’t quite time. Just tuck them back into the flat and leave them for one more day. Once you remove the towel, watch your micro-greens grow!
Keep their soil moist, and ensure that they are getting enough light (they can get leggy if they aren’t) and when they have their first true leaf, it is time to harvest. Although, if you just can’t wait, you can harvest them when they only have their cotyledons.
* Keep in mind that the amount of seed needed can vary significantly. For most other brassicas, I would suggest trying 1 tablespoon of seed per flat to start. You want the flats flush with greens, but over-seeding can cause uneven growth and stunted micro-greens. You’ll get a better sense of the amounts you need after you grow a couple flats
To harvest, take your sharp scissors, gently grasp a handful of micro-greens in a corner, and snip them toward the base of the plant, but high enough not to bring soil into the mix. If they are leggy, you will want cut a little higher.