Microgreens are edible seedlings harvested shortly after the cotyledons have fully developed, but usually before the first true leaves appear. They are distinct from sprouts because they are grown in soil or a substrate, and only the stem and leaves are consumed. Growing microgreens in a soil medium is often preferred by home cultivators for its relative simplicity and the slightly richer flavor profile soil can impart. This guide focuses exclusively on the soil-based technique for growing these nutrient-dense greens indoors.
Essential Materials and Pre-Sowing Preparation
Successful microgreen cultivation begins with selecting the correct growing medium and container. Shallow trays, only one to two inches deep, are commonly used since microgreen root systems are shallow. Growers often utilize two types: one with drainage holes for growing, and a solid tray placed beneath it to act as a reservoir for bottom watering.
The choice of substrate directly influences seed germination and overall plant health. Growers should select a fine-textured, sterile, soilless potting mix or coco coir, avoiding heavy garden soil which can compact and harbor pathogens. A light, fluffy substrate provides the necessary aeration for root growth and ensures adequate drainage, preventing the environment from becoming overly saturated and anaerobic.
Selecting appropriate seeds is important, with popular choices including radish, broccoli, and sunflower, which offer quick growth and robust flavor. Larger seeds, such as sunflowers and peas, benefit significantly from a pre-soaking period of four to twelve hours. This initiates the imbibition process, softening the seed coat and accelerating germination rates. Smaller seeds like broccoli, kale, or radish should not be soaked, as they are prone to damage or rot if left submerged.
Sowing the Seeds and Initiating the Blackout Phase
Once materials are prepared, the growing medium must be properly conditioned in the tray. The soilless mix should be moistened thoroughly before seeding until it is uniformly damp, but not soggy. It should then be gently tamped down to create a level surface. This firming action eliminates air pockets and ensures that all seeds make consistent contact with the substrate, leading to uniform germination.
Seeds are then sown densely across the prepared surface, aiming for a single layer that completely covers the soil without significant overlapping. This high-density planting maximizes yield per square inch, but requires proper post-sowing management to prevent mold. The seeds are not covered with an additional layer of soil.
Immediately following seeding, the tray should be misted lightly one last time, and then the blackout phase begins. This involves covering the tray with a humidity dome or, more effectively, placing an identical tray directly on top and adding weight, such as a brick or ballast. Applying pressure encourages the seedlings to grow strong, fibrous root systems as they push against the resistance. The darkness stimulates etiolation, causing the stems to lengthen uniformly. This initial phase typically lasts between two and four days, maintained until the majority of the seedlings have germinated and visibly lift the weight of the cover.
Providing Light, Maintenance, and Harvesting
The transition to light exposure is signaled when emerging seedlings begin to push up the weighted cover, indicating established root systems and sufficient stem elongation. Removing the cover introduces light, which immediately halts etiolation and triggers chlorophyll production, turning the pale yellow stems vibrant green. While a south-facing window can provide adequate light, a dedicated grow light positioned a few inches above the canopy is often preferred. This ensures high-intensity illumination and prevents the seedlings from becoming “leggy.”
Watering technique shifts dramatically once the greens are exposed to light to prevent fungal diseases like “dampening off.” Misting is discontinued; water is instead added to the solid bottom tray, allowing the growing medium to absorb moisture via capillary action. Bottom watering keeps the delicate cotyledons and stems dry, which inhibits the growth of common molds that thrive on humid foliage. The roots will grow downward into the reservoir, efficiently managing their own water uptake.
Maintaining gentle airflow around the trays is a simple yet effective measure against fungal outbreaks. A small circulating fan set on a low speed mimics natural air movement, helping to evaporate moisture from the growing medium and the leaves. This constant air exchange is effective in maintaining a low-humidity environment directly surrounding the plant stems.
Determining the precise moment of harvest is based on the developmental stage of the plant, not a specific number of days. Microgreens are optimally harvested when the cotyledons are fully open and the stems are robust, just before or as the first set of true leaves begins to emerge. The appearance of true leaves often signals a decline in the concentrated nutrient profile and flavor intensity. The harvest window is typically a short period of only a few days for most varieties.
To harvest, use a sharp, clean knife or scissors to cut the stems just above the surface of the soil. This technique ensures that no soil or growing medium is included in the final product. While the remaining roots and stems will not regrow a second harvest, the careful harvest yields a concentrated, flavorful product ready for immediate consumption.