Microgreens, the young seedlings of edible vegetables and herbs, are popular for their concentrated nutrient profiles and simple cultivation. While traditionally grown in soil, soilless methods offer a cleaner, more controlled, and efficient alternative for indoor growers. This approach uses inert, sterile substrates, drawing on hydroponic principles to support the plant physically while water delivers moisture and nutrients. Eliminating soil mitigates the risk of soil-borne pathogens and simplifies harvesting, resulting in a cleaner final product.
Selecting the Best Soilless Growing Mediums
Choosing the correct substrate is important in soilless microgreen cultivation, as the medium serves primarily as an anchor and a water reservoir rather than a nutrient source. One widely adopted option is coconut coir, a byproduct of coconut processing, which boasts excellent water retention and aeration. Coco coir maintains moisture well without becoming waterlogged, a balance that is important for delicate microgreen roots. Its neutral pH and natural resistance to pests make it a sustainable choice for many indoor setups.
Another popular choice is the use of hydroponic grow mats, typically made from natural fibers like hemp or jute. Hemp mats are valued for their cleanliness, biodegradability, and fibrous structure that anchors the seeds firmly, promoting uniform growth. These mats are inert, providing no nutrients, which is acceptable since microgreens rely on the seed’s stored energy and water for their short life cycle. Specialized cellulose pads or rockwool are also used, offering a clean and sterile environment.
The Step-by-Step Soilless Cultivation Process
The soilless growing process begins by preparing the chosen medium, such as a hemp mat, by thoroughly hydrating it in a growing tray with drainage holes. The mat should be fully saturated but not submerged, allowing excess water to drain away. Larger seeds, like sunflower or pea, benefit from being pre-soaked for eight to twelve hours to accelerate germination, though many smaller seeds are sown dry.
The seeds are then densely and evenly broadcast across the surface of the wet mat, aiming for coverage where the seeds nearly touch without significant overlap. Overcrowding can inhibit airflow and increase the risk of fungal issues, making a calculated seeding rate important. After seeding, the tray should be lightly misted and immediately covered with a blackout dome or another tray to create a dark, humid environment that encourages uniform germination.
This blackout period, often lasting two to four days, allows the seedlings to establish root systems and grow taller in search of light (etiolation). Placing a small weight on the cover encourages stronger, thicker stems as the seedlings push against the resistance. Once the seedlings have visibly lifted the cover and their first embryonic leaves (cotyledons) have emerged, the tray is transitioned out of blackout and exposed to light. Watering should primarily be done from the bottom, pouring water into the base tray so the mat can wick up moisture. This bottom watering keeps the delicate seedlings dry and minimizes the risk of mold.
Troubleshooting and Maintaining Your Soilless Crop
Soilless environments, with their high-density planting and humidity, carry an increased risk of mold or fungal growth. The most common defense is maintaining strong air circulation, often by using a small oscillating fan to gently move air across the plant canopy. This airflow strengthens the stems and prevents stagnant moisture from settling, which triggers pathogens like Botrytis.
Controlling the environment’s temperature and humidity is important, aiming for a relative humidity between 50 and 65 percent and a temperature range of 65 to 75 degrees Fahrenheit after germination. If a fuzzy white growth appears, growers must distinguish between harmful mold and harmless root hairs. Root hairs can be identified by misting the area; true mold will not dissipate, while root hairs will temporarily collapse.
The greens require 12 to 16 hours of light daily, often supplied by full-spectrum LED grow lights. These lights should be positioned approximately 6 to 12 inches above the canopy to ensure adequate intensity and prevent stretching. When the microgreens reach two to four inches in height and have developed their first true leaves, they are ready for harvest. Harvesting is accomplished by cutting the stems just above the growing mat with a sharp, clean blade.