Microgreens are immature vegetable greens harvested shortly after the cotyledon leaves have fully developed, offering concentrated flavor and nutrition. Unlike sprouts, which are eaten root and all, microgreens are cut just above the medium. Cultivating these plants without traditional potting mix is known as soilless or hydroponic growing. This method provides a cleaner, more controlled environment for rapid development, making it highly effective for indoor setups.
Essential Supplies for Hydroponic Growing
Setting up a successful soilless microgreen system requires specialized equipment. Growers need two types of containers: a shallow, slotted tray to hold the medium and seeds, and a solid tray without holes to act as a reservoir for bottom watering. These trays should be paired with a clear humidity dome or cover, which maintains the high moisture levels necessary for initial germination.
High-quality microgreen seeds are necessary, as they must be planted at a much higher density than garden seeds. The final specialized item is a full-spectrum LED grow light, which provides the necessary photosynthetically active radiation (PAR) for healthy growth. These lights should be adjustable to maintain a distance of 6 to 12 inches above the developing greens.
Selecting the Soilless Medium
The choice of growing medium is central to soilless cultivation, serving as the substrate that anchors the roots and holds moisture. Natural fiber mats, such as those made from hemp, jute, or bamboo fibers, are a popular choice. They offer exceptional water retention and are easy to handle. Mats are often preferred for their cleanliness and simplicity, as they can be composted easily after harvesting and reduce the risk of debris contaminating the final product.
Coco coir, a byproduct made from the outer husk of coconuts, is another effective option. It provides excellent aeration and maintains a naturally pH-neutral environment. While coco coir must be hydrated thoroughly before use, its structure prevents compaction, allowing delicate microgreen roots to breathe effectively.
Inert substrates, including materials like perlite, vermiculite, or rockwool, are primarily used in larger commercial hydroponic setups. These materials require a diluted nutrient solution from the first day, as they provide no inherent nutrition. For the rapid 7- to 14-day growth cycle, fiber mats and coco coir are simpler for home growers because they retain enough moisture and initial nutrition for the plants to thrive.
Step-by-Step Soilless Cultivation
Starting the soilless cultivation process requires careful preparation of the chosen growing medium. If using a mat, thoroughly soak it in water and place it into the slotted tray, ensuring excess water has drained completely. Coco coir must also be fully saturated and then spread evenly across the tray to a depth of about a half-inch.
Once the medium is prepared, distribute the seeds densely and uniformly across the entire surface. Unlike garden planting, microgreen seeds should be touching or nearly touching to maximize the final yield. After sowing, most seeds do not require a layer of medium on top, but a light misting of water helps settle them onto the surface.
The next phase is the blackout or germination period, which lasts between two and four days depending on the seed type. During this time, the tray is placed in complete darkness, often with another tray placed on top to apply gentle pressure, known as “stacking.” This pressure encourages the seedlings to develop strong root systems and pushes them downward into the medium.
After the roots have anchored and the shoots are about an inch tall, move the trays into the light source for the growth phase. Seedlings require 12 to 18 hours of light per day, which encourages the development of chlorophyll and the greening of the cotyledons. Maintaining air circulation with a small fan helps prevent fungal growth.
Water delivery shifts once the trays are exposed to light. Microgreens must be watered from the bottom by pouring water directly into the solid reservoir tray, allowing the medium to wick up moisture through the drainage holes. This technique, known as bottom watering, keeps the leaves and stems dry, preventing mold and damping off disease. Because microgreens are harvested quickly, they rarely require supplemental nutrients, though varieties like peas or sunflowers may benefit from a diluted hydroponic solution after seven days of growth.
Harvesting and Troubleshooting Common Issues
Determining the ideal harvest time maximizes both flavor and nutrient content. Most microgreens are ready when the cotyledons are fully expanded, or just as the first set of true leaves begins to emerge, typically 7 to 14 days after planting. Harvest using a sharp knife or scissors, cutting the stems cleanly just above the medium surface to avoid collecting root material.
Soilless growing can be prone to two issues that require quick intervention. Mold or fungus appears as white, fuzzy growth on the stems or medium, usually caused by poor air circulation and high humidity. Increasing airflow with a small oscillating fan and ensuring the top surface of the medium dries slightly can resolve this problem. Damping off is a fungal disease that causes seedlings to collapse at the base. This is best prevented by using clean trays and strictly adhering to the bottom watering technique. Harvested microgreens should be consumed immediately or stored unwashed in a sealed container in the refrigerator for up to a week.