Microgreens are young seedlings of edible vegetables and herbs, typically harvested within one to three weeks after germination, before their first true leaves emerge. They are valued for their concentrated flavor and high nutritional content, often exceeding that of their mature counterparts. Growing these greens without soil (soilless or hydroponic cultivation) is popular because it offers a clean, efficient, and space-saving alternative to traditional gardening. This method eliminates mess and potential soil-borne pests, allowing for year-round production indoors.
Selecting Seeds and Substrate
Soilless microgreen growing starts with selecting appropriate seeds and a substrate. Brassica seeds, such as broccoli, radish, and kale, are excellent choices for beginners because they germinate reliably and grow quickly. Larger seeds like peas and sunflowers also thrive, though they often require pre-soaking to initiate germination.
The substrate replaces the soil and must retain moisture while providing aeration for root development. Two common soilless media are coco coir and hemp mats. Coco coir, derived from coconut husks, is a sustainable option that holds water well and provides a neutral pH environment. Hemp mats are a biodegradable alternative that absorbs up to ten times their weight in water, offering a clean, easy-to-handle option that simplifies harvesting.
Essential Equipment and Environmental Control
Setting up a controlled growing environment requires equipment for consistent, healthy microgreen development. The system uses two nested trays: a shallow tray with drainage holes to hold the substrate, and a solid tray underneath to act as a water reservoir. This setup facilitates the preferred bottom-watering technique.
Since microgreens grow indoors, an artificial light source is needed. Energy-efficient LED grow lights should be suspended 12 to 18 inches above the trays and run for 12 to 16 hours daily. A humidity dome or cover is temporarily required during initial germination to trap moisture and create a mini-greenhouse effect. Maintain the room temperature between 65 and 75 degrees Fahrenheit. Adequate air circulation, often provided by a small fan, is necessary to keep humidity between 40% and 60% and prevent fungal growth.
The Soilless Microgreen Cultivation Process
Cultivation begins by preparing the soilless substrate, soaking it until damp. For large seeds like peas, an eight-hour soak in clean water before planting improves germination rates. Once the substrate is prepared, spread seeds densely and evenly across the surface, avoiding thick clumps that restrict airflow.
After seeding, the tray is lightly misted and placed into the blackout phase for two to four days. This involves covering the tray or stacking a weighted tray on top, encouraging seedlings to grow tall while establishing roots in search of light. Once seedlings have visibly lifted the cover and developed a yellowish hue, move the tray under the grow lights.
The primary watering technique is bottom-watering, which introduces water into the reservoir tray beneath the growing media. The substrate wicks moisture upwards into the roots, keeping the surface dry to reduce the risk of mold and damping-off disease. Add water as needed, typically once or twice daily, to maintain consistent moisture without allowing roots to sit in stagnant water.
Troubleshooting and Harvesting
A common issue is the appearance of fine, white fuzz around the base of seedlings, often mistaken for mold. This is usually harmless root hair, which disappears when misted with water. True mold resembles spider webbing and will not change when misted. Mold results from high humidity or poor air circulation and is prevented by increasing airflow with a fan and using bottom-watering.
Uneven germination can be caused by low-quality or old seeds, or inconsistent moisture during the blackout period. Ensuring the substrate is uniformly moist before seeding and maintaining a stable temperature range promotes simultaneous sprouting. Microgreens are ready for harvest once they have developed their cotyledons (seed leaves) and before the first true leaves emerge. Harvesting is simple: cut the greens just above the substrate surface using a sharp knife or scissors. Store the harvested greens unwashed in an airtight container in the refrigerator to maintain freshness.