Microgreens are immature vegetable seedlings, and arugula is a particularly fast-growing and popular choice among them. These tiny greens are harvested just after the cotyledon leaves have fully opened, typically before the first true leaves appear. Arugula microgreens offer a concentrated, peppery flavor that is far more pungent than the mature plant. Their rapid life cycle, often from seed to harvest in under two weeks, makes them an excellent project for growing fresh produce indoors year-round.
Supplies and Preparation
Growing microgreens requires specific materials for a successful, dense crop. You will need two shallow trays: one with drainage holes for the growing medium, and one without holes for a water reservoir and blackout cover. Use a fine-textured, sterile medium like coco coir or a seed-starting potting mix.
Acquire seeds specifically intended for microgreens, as these are tested for high germination rates and cleanliness. A basic light source, such as a fluorescent fixture or an LED grow light, is also required. Before planting, fill the drainage tray with a level layer of moistened medium, about one to two inches deep, and gently tamp it down to create a smooth surface.
Seeding Density and Initial Germination
Arugula seeds do not require pre-soaking and are sown directly onto the prepared medium. The optimal seeding density is thick, aiming for an even, edge-to-edge spread across the entire tray surface. This high density encourages seedlings to grow tall and straight as they compete for light, which is a desirable trait for microgreens.
After distributing the seeds, lightly mist the surface with water to ensure good seed-to-medium contact, avoiding over-saturation. Next is the blackout phase: cover the tray with the second, solid tray and place it in complete darkness for two to four days. This encourages the seedlings to stretch and develop strong root systems.
Because arugula is prone to dampening off, placing a light weight (five to fifteen pounds) on the top tray during blackout is helpful. The pressure forces the germinating roots to anchor firmly into the medium. When the sprouts are ready, they will be about half an inch tall and appear yellow due to the lack of light.
Light, Watering, and Care
After the blackout period, move the tray immediately into the light, allowing the stems to green up rapidly. The seedlings require twelve to eighteen hours of light daily. Position the grow light close enough to prevent them from becoming overly leggy; keeping the light too far away causes excessive stretching and thin, weak stems.
Bottom-watering is the preferred method, performed by pouring water into the solid tray beneath the drainage tray. The medium draws water up via capillary action, keeping the cotyledons dry. This technique prevents wet foliage, which can quickly lead to fungal issues like mold or damping off in densely packed microgreens.
Maintain good air circulation with a small fan to control humidity and reduce the risk of mold. Water the plants only when the tray feels noticeably lighter, ensuring the medium remains consistently moist but never waterlogged.
Harvesting and Storage
Harvest arugula microgreens when the cotyledons are fully expanded and the plants are approximately one to three inches tall. Harvesting must occur before the first true leaves emerge, as the flavor intensifies significantly afterward. Once true leaves appear, the plant’s energy shifts, and the texture can become less tender.
Use sharp scissors or a clean knife to cut the stems just above the soil line. Cutting cleanly minimizes damage and prevents contamination. Do not wash the greens before storage, as excess moisture drastically reduces their shelf life.
Store the cut microgreens unwashed and dry in a loosely covered container, such as a plastic clamshell lined with a paper towel, in the refrigerator. Washing should only be done immediately before consumption.