Cilantro (Coriandrum sativum) is a popular herb prized for its distinct flavor profile. Starting seeds indoors offers a continuous, year-round supply, independent of seasonal weather changes. This approach provides greater control over the environment, which is necessary because cilantro requires specific, cool conditions to flourish and produce flavorful leaves. Successfully growing this herb involves managing its life cycle from the initial seed stage through to regular harvest.
Essential Supplies for Indoor Seed Starting
Selecting the correct materials sets the stage for healthy seedling development. Containers should be shallow, approximately 3 to 4 inches deep, as cilantro prefers well-drained conditions and does not develop an extensive root system initially. The growing medium must be sterile and formulated for seed starting, providing light aeration and excellent drainage to prevent fungal issues like damping off. Using fresh seeds is highly recommended, as cilantro seed viability decreases significantly after only a year.
The cilantro seed is botanically a schizocarp, a dried fruit containing two separate seeds encased in a hard husk. To improve germination, the seeds benefit from a preparatory soak. Placing them in room-temperature water for 12 to 24 hours helps soften the tough outer shell, allowing moisture to penetrate the embryo more quickly. This step can shave several days off the typical germination period.
Preparing and Sowing the Cilantro Seeds
Once the seeds are prepared, fill the containers with the sterile seed-starting mix. Gently tamp the surface of the growing medium to create a level, firm base without compacting the soil excessively. If the seeds were not pre-soaked, gently breaking the dried fruit husk can free the two seeds inside, though this must be done carefully to avoid damaging the inner embryos.
Cilantro seeds should be planted at a shallow depth, typically about one-quarter to one-half inch below the soil surface. Proper spacing is important to reduce competition for resources and light. Aim to place individual seeds or small clusters of two seeds approximately two inches apart within the container.
After the seeds are positioned, lightly cover them with the remaining growing medium and gently press the surface. Initial watering should not be done with a heavy stream, which can dislodge the shallowly planted seeds. Instead, mist the surface with a spray bottle, or use bottom watering by placing the container in a tray of water until moisture wicks up to the top layer of the soil. This provides uniform hydration without disturbing the seeds.
Creating the Ideal Germination Environment
Successful sprouting relies on a steady environment maintained around 70 to 75 degrees Fahrenheit. This temperature range encourages the metabolic activity within the seed embryo to break dormancy. If the ambient room temperature is cooler, a specialized seedling heat mat placed beneath the containers can provide the consistent warmth needed.
Maintaining high humidity is equally important during this phase to prevent the seeds from drying out. Covering the containers with a clear plastic dome or plastic wrap traps moisture and creates a miniature greenhouse effect. This dome should remain in place throughout the germination period.
During the initial sprouting phase, light is not strictly required because the seedling draws energy from stored resources within the seed. Consistent moisture and stable temperature are the primary factors driving successful germination. The plastic cover should be monitored daily, and a fine mist applied if the soil surface appears to be drying out.
Maintaining Indoor Growth and Preventing Early Bolting
Once the first sprouts emerge from the soil, the humidity dome or plastic cover must be promptly removed. The seedlings now require intense light to develop strong stems and proper leaf structure. Indoor cilantro necessitates the use of supplemental grow lights, such as full-spectrum LEDs or fluorescent fixtures, positioned close to the plants. The light should be provided for 14 to 16 hours daily.
The most common reason for indoor cilantro failure is premature bolting, which occurs when the plant shifts energy from leaf production to flower and seed production. This process is triggered primarily by heat stress. Maintain the surrounding air temperature below 70 degrees Fahrenheit, ideally between 60 and 68 degrees, as higher temperatures cause the plant to produce bitter-tasting compounds.
When the seedlings develop their second set of true leaves, they should be thinned to ensure proper air circulation and light penetration. Gently snip the weaker seedlings at the soil line, leaving the strongest plants spaced about four to six inches apart. Overcrowding contributes to stress and bolting.
Ongoing watering involves allowing the top half-inch of the soil to dry slightly between waterings, preventing root saturation while maintaining even moisture. For harvesting, use the “snip-and-come-again” technique: cut outer stems and leaves near the base, leaving the central growing point intact. This encourages the plant to produce new foliage continuously.