Microgreens grow best in bright sites indoors. Young seedlings are vulnerable to heavy rain, wind and other extreme weather conditions, so grow microgreens in a greenhouse, conservatory or on a bright, south-facing windowsill. Most flat, plastic containers with drainage holes are fine for growing microgreens, and most soilless growing media can support the young plants, including a folded sheet of burlap, or a 3/4-inch layer of peat, coconut fiber, vermiculite or perlite. Fibrous seedling mats are made especially for growing microgreens and sprouts. Use pesticide-free seeds for microgreens. The time to harvest varies between plants, so usually just one variety is sown per container. Lettuce (Lactuca sativa), an annual plant, isn't suitable because its leaves are soft when young.
Moist growing sites promote fast, healthy growth in microgreens, but too much water encourages diseases. Microgreen seeds need water to germinate, but after the seeds have sprouted it's best to water from the base of the plants to avoid wetting the leaves. Stand the sprouted microgreens container in a sink or shallow bowl containing 1 inch of water every day. As soon as the water appears on the surface of the growing medium, lift the container out of the water and place it somewhere it can drain freely. In very hot weather, microgreens might need more frequent watering. Check the plants and water them whenever the growing medium surface is dry. Use only well or tap water for watering microgreens, because water from a pond or rain water barrel can contain disease-causing organisms.
Feeding Young Plants
Plants that take longer than most other microgreens to grow to harvest benefit from a weak fertilizer application. Most microgreen plants are harvested very young and don't require feeding, but carrots (Daucus carota var. sativus), dill (Anethum graveolens) and other slow-growing microgreens grow best with one light fertilizer application. When the second set of leaves emerge, dilute an 8-0-0 liquid fertilizer at a rate of 1/4 teaspoon per 6 cups of water, and float the microgreens container in the solution for 30 seconds. Lift out the container and allow it to drain. Manufacturer's instructions vary between products, so follow the instructions on the label, but double the dilution rate to create a weak solution.
Harvest time for microgreens is seven to 21 days after sowing, or when the plants are about 2 inches tall. Snip the leaves with scissors, or if the microgreens are growing on burlap or a seedling mat, hold the sheet up in one hand and run an electric knife down it with the other hand. For the freshest leaves, harvest microgreens just before eating them. Microgreens wilt quickly after cutting. The roots are exhausted by harvest time, and should be discarded.