Microgreens are the "child" stage of certain plants, usually quite tender and tasty, and possessing great nutritional value.
As awesome as these are for getting living greens and enzymes throughout the winter, it takes a metric assload of seeds to constantly supply microgreens, so there really aren't the most sustainable long-term solution.
Researchers at the USDA Agricultural Research Service have published, as of early 2014, several studies that identify the nutritional make-up and the shelf life of microgreens. Twenty-five varieties were tested, key nutrients measured were ascorbic acid (vitamin C), tocopherols (vitamin E), phylloquinone (vitamin K), and beta-carotene (a vitamin A precursor), plus other related carotenoids in the cotyledons.
Among the 25 microgreens tested, red cabbage, cilantro, garnet amaranth, and green daikon radish had the highest concentrations of vitamin C, carotenoids, vitamin K, and vitamin E, respectively. In general, microgreens contained considerably higher levels of vitamins and carotenoids—about five times greater—than their mature plant counterparts, an indication that microgreens may be worth the trouble of delivering them fresh during their short lives.
A nutritional study of microgreens was done in the summer of 2012 by the Department of Nutrition and Food Science, University of Maryland, indicating promising potential that microgreens may indeed have particularly high nutritional value compared to mature vegetables. Bhimu Patil, a professor of horticulture and director of the Vegetable and Fruit Improvement Center at Texas A&M University, agrees that microgreens may potentially have higher levels of nutrients than mature vegetables. But he says more studies are needed to compare the two side by side. "This is a very good start, but there can be a lot of variation in nutrients depending on where you grow it, when you harvest, and the soil medium," Patil says. When choosing a microgreen, researchers say to look for the most intensely colored ones, which will be the most nutritious. Results of the microgreens research project conducted by the University of Maryland and the USDA has garnered attention from several national media outlets including National Public Radio (NPR) and The Huffington Post.