Microgreens are young, edible seedlings of various vegetables and herbs, typically harvested within 7 to 21 days after germination. They are celebrated for their concentrated flavors, vibrant colors, and high nutritional density, often containing higher levels of vitamins and antioxidants than their mature counterparts. The short, rapid growth cycle of microgreens is a defining characteristic, and this brief cultivation window dictates their unique nutritional needs.
The Core Principle: Seed Energy and Short Cycles
The majority of microgreens do not require supplemental fertilizer because they complete their life cycle using their own stored resources. Every seed is a self-contained nutritional package, loaded with complex carbohydrates, fats, and proteins. These substances are the plant’s initial fuel source, contained within the endosperm or the cotyledons.
The cotyledons, or “seed leaves,” are the first embryonic leaves to emerge, and they function as the nutrient battery for the seedling. They draw on the seed’s reserves to power the initial growth spurt, allowing the plant to develop a stem and unfurl its first pair of leaves. By the time microgreens are harvested—typically at the cotyledon stage or just as the first true leaves appear—they have not exhausted the seed’s original energy supply.
The Function of the Growing Medium
If external fertilizer is not typically needed, the growing medium serves a different, yet equally important, set of functions. The primary role of the medium is to provide stable structural support, anchoring the tiny root systems of the dense planting. This physical base allows the seedling to stand upright against the weight of the seed hull and gravity.
The medium acts as a reservoir for consistent hydration and aeration. Materials like coconut coir, peat-based mixes, and hemp mats are selected for their ability to retain moisture while simultaneously allowing oxygen to reach the roots. Traditional soil mixes used are often nutrient-poor and sterile, functioning primarily to manage water and air flow, not to feed the plant.
Scenarios Requiring Nutrient Supplementation
While many microgreens thrive without added nutrients, there are specific scenarios where supplementation becomes necessary. The need for fertilizer is dictated by the plant species and the growing method.
Extended Growth Cycles
Larger-seeded crops, such as peas and sunflowers, are often grown for a longer period, sometimes until their first set of true leaves develops. This extended growth cycle, lasting beyond the point where the seed’s reserves are sufficient, may benefit from a small nutrient boost to maximize yield and quality.
Hydroponic Systems
Any purely hydroponic setup, which uses inert substrates like hemp fiber mats, requires an external nutrient solution. Since these soilless mediums provide zero inherent nutrition, the water must be fortified to supply the essential macronutrients like nitrogen, phosphorus, and potassium (NPK), as well as various micronutrients. The solution used must be highly diluted compared to that used for mature plants, often mixed at a fraction of the recommended strength to prevent damage.
Risks and Application
Misapplication of fertilizer can lead to significant problems. Using a solution that is too concentrated can cause root damage, known as “nutrient burn,” due to excessive salt accumulation. High levels of nitrogen can sometimes contribute to the development of mold or fungal issues, especially in the high-density planting environment of a microgreen tray. A balanced NPK fertilizer is needed, typically applied only after the cotyledons have fully emerged and the plant has been exposed to light.