Microgreens are the young seedlings of various vegetables, herbs, and other plants, harvested just after the cotyledon leaves have fully developed. This growth window typically lasts between 7 and 21 days, depending on the species being grown. Because of this short cultivation period, a common question arises about whether these tiny plants require external fertilization to thrive. The answer depends heavily on the specific stage of development and the medium used for growth.
Seed Power vs. External Feeding
The initial growth of a microgreen seedling is powered entirely by the energy and nutrients stored within the seed itself. This stored reserve, contained within the endosperm or the cotyledons, acts as the plant’s first food source. These internal stores provide all the necessary macronutrients, such as nitrogen, phosphorus, and potassium, required for germination and the rapid development of the first leaves.
For many microgreen varieties, harvested shortly after the cotyledons appear, this internal energy is often sufficient to complete the entire life cycle without added fertilizer. Introducing external nutrients during this initial phase is unnecessary and can even be counterproductive. High concentrations of fertilizer salts can lead to “nutrient burn,” which damages delicate root structures and stunts growth.
Timing the Nutrient Introduction
The need for external nutrients is directly linked to the plant’s transition from relying on seed reserves to performing full-scale photosynthesis. This transition is visually marked by the emergence of the first set of “true leaves,” which appear after the initial, rounded cotyledons. The appearance of these true leaves signals that the internal energy reserves from the seed are becoming depleted, and the plant is entering a period of rapid growth that requires external feeding.
For microgreens with longer harvest cycles, such as peas or sunflowers, reaching the true leaf stage means the plant needs supplemental feeding to maintain vigor and maximize yield. Failure to introduce nutrients can lead to visible signs of deficiency, such as general yellowing (chlorosis) or stunted growth. Yellowing starting at the lower leaves often indicates a nitrogen deficiency, as the plant mobilizes nutrients from older tissue to support new growth.
Nutrient Delivery Based on Growing Medium
The method of delivering external nutrients is determined by the choice of growing medium. When cultivated in a soil-based substrate, such as a peat or coir-based potting mix, supplemental feeding is rarely required for the microgreen’s short life cycle. These mixes typically contain enough residual organic matter and buffered nutrients to sustain the plants until harvest. The soil itself acts as a reservoir, slowly releasing nutrients to the developing roots.
In contrast, soilless methods, including hydroponic mats, coco coir, or rockwool, are inert and contain no inherent nutritional value. For these setups, external nutrients must be provided entirely through the irrigation water once the true leaf stage is reached. Growers typically use a balanced, water-soluble fertilizer formulated for leafy greens, diluted to one-quarter or one-half the strength recommended for mature plants. This diluted solution ensures the plants receive necessary macro and micronutrients without the risk of high salt buildup. Monitoring the electrical conductivity (EC) and pH is necessary in soilless systems to ensure optimal nutrient uptake and prevent toxicity.