Microgreens are the quickest and most intensive crop that we grow. Parsnips take 120 days from seeding to harvest, heads of lettuce can be grown in about 60 days, while radishes and arugula, our quickest crops in the field, can be harvested as soon as 3 weeks after planting during the height of the summer. Microgreens can be sown and then harvested within a week to a week and a half, making them a fantastic crop to get us through the short days of winter when everything grows super-slowly. And while you might think that they are only useful as a fancy little garnish, they pack a real wallop in terms of both flavor and the phytonutrients that are the reason your mom told you to eat your greens! One study found that microgreen seedlings of red cabbage, cilantro, and radish had up to 40 times concentration of the vitamin E, C, K, lutein, and beta-carotene of their mature counterparts!
So how do we grow these tasty little treats in the winter? I often like to think of our protected structures in terms of a pyramid from the least protected structures, which are cheaper and so we can cover more ground with them (right now the caterpillars where we are harvesting kale are the bottom floor of the pyramid) up to the most protected zones. Microgreens come from the very top of the pyramid, the heated bench in our main greenhouse. We have a wood pellet boiler that produces hot water used to power a radiator that keeps that main greenhouse just above freezing all winter long. The main body of the greenhouse is a great place for the salad mix, lettuce mix, chard, arugula, and pea shoots that grow during the balmy but short days and then hang out for the long but not-quite freezing winter nights. That hot water is also circulated through tubes in two 5′ X 30′ benches that we use to start seedlings for transplanting out into other greenhouses, and eventually into the field. We also use that heat to start microgreens. The seeds for the microgreens are thickly sown in flats, and then lightly covered with vermiculite. With some nice heat from underneath, they pop up and are ready for harvest lickety-split! You can just barely see the germinating seedlings in the picture below, a day and a half after planting: