The lifespan of microgreen seeds is determined by a gradual loss of viability, which is the seed’s ability to germinate. Seeds are living organisms whose internal cell structures slowly degrade over time. For microgreen growers, the primary concern is whether a high percentage of a batch will sprout uniformly and vigorously enough to produce a dense, marketable crop. Successful microgreen production demands a much higher germination rate than traditional gardening, meaning seeds are often considered unusable long before a home gardener would discard them.
Baseline Viability of Microgreen Seeds
Under typical conditions, most microgreen seeds can maintain acceptable viability for one to five years, though this range varies significantly by species. Seeds from the Brassica family, such as broccoli, kale, and radish, are known for their relatively long shelf life, often remaining viable for four to five years. Conversely, seeds like onions, parsley, and certain herbs tend to be shorter-lived, sometimes only retaining good viability for one or two years. Seeds from legumes, like peas, generally fall in the middle of this range.
The requirement for a high-density crop makes the viability standard for microgreens particularly demanding. Microgreen growers typically aim for a germination rate of 85% or higher, whereas a traditional gardener might tolerate 60%. A lower rate results in patchy trays, wasted space, and inconsistent harvest yields. This means seeds become functionally “expired” for commercial purposes much sooner than their absolute biological limit, often necessitating a much higher seeding density to compensate for even a slight drop in germination percentage.
Critical Factors Governing Seed Storage
The longevity of microgreen seeds is primarily controlled by three environmental factors: temperature, moisture, and light, all of which a grower can actively manage. The central goal of proper storage is reducing the rate of metabolic degradation within the seed.
Temperature control is a powerful tool for extending seed life, with cooler environments significantly slowing down the aging process. Storing seeds in a refrigerator (around 40°F or 4°C) or even a freezer can extend their viability for many years beyond room temperature storage. When utilizing cold storage, it is important to ensure the seeds are completely dry before placing them in the cold to prevent moisture from condensing and causing damage.
Moisture content within the seed itself is the single biggest threat to long-term viability. High moisture levels accelerate the chemical reactions that cause aging and make the seeds susceptible to mold and fungal growth. The best practice is to store seeds in an airtight container to prevent them from absorbing ambient humidity. Adding a desiccant, such as silica gel or powdered milk wrapped in a tissue, inside the sealed container helps absorb residual moisture and maintain a low relative humidity environment.
Light exposure also contributes to the degradation of a seed’s internal components, so seeds should always be stored in a dark location. A sealed, opaque container stored inside a dark cabinet or a refrigerator is the ideal setup to protect against light, temperature fluctuations, and humidity. Combining low temperature and low moisture creates the most stable environment for preserving the high germination rate necessary for microgreen production.
Practical Methods for Assessing Seed Health
Before committing a large quantity of seed to a tray, especially older stock, a simple germination test can reliably assess the current seed health. The paper towel test is a straightforward method that mimics the ideal conditions for sprouting. A grower counts out a sample of seeds (typically 10, 20, 50, or 100) and places them between moist paper towels or on a paper coffee filter.
The moist paper is then placed inside a sealed plastic bag or container to maintain humidity and kept in a warm spot out of direct sunlight. After the typical germination period for that species, which is often three to seven days, the number of sprouted seeds is counted. The percentage of seeds that germinated successfully is the current germination rate for that seed lot.
A visual inspection is a quick, initial assessment that can complement the germination test. Healthy seeds should appear uniformly colored, plump, and free of discoloration, mold, or unusual smells. If the germination test yields a rate below 70%, the seeds are likely too degraded for efficient microgreen cultivation. Rates between 70% and 85% may require the grower to increase seeding density to compensate, while anything above 85% is considered excellent for production.