Growing cherry tomatoes from seed indoors allows gardeners to bypass the short outdoor growing season. This practice ensures plants are robust and mature enough to thrive immediately after the last frost, leading to an earlier and more abundant harvest. Starting seeds inside provides complete control over the initial environment, establishing strong root systems and healthy growth. This guide outlines the steps necessary to transition seeds into vigorous seedlings ready for the garden.
Calculating Start Time and Gathering Supplies
The moment to sow cherry tomato seeds indoors is determined by the average date of the last expected frost in your area. A general guideline is to begin approximately six to eight weeks before this projected outdoor planting date. Starting seeds too early often results in leggy, overgrown plants that suffer from nutrient deficiencies and transplant shock when moved outside.
Success begins with gathering sterile materials to prevent fungal issues like damping off disease. Acquire a sterile, fine-textured seed starting mix, as regular garden soil is often too dense and may harbor pathogens. Select appropriate containers, such as small cell trays or biodegradable peat pots, ensuring they have adequate drainage holes. Finally, cherry tomato seeds and a clear plastic dome or wrap are needed to maintain high humidity for initial germination.
Planting the Seeds
Before planting, the seed starting mix must be thoroughly moistened until it feels like a wrung-out sponge, allowing for uniform moisture without becoming waterlogged. This pre-moistening is important because attempting to water dry soil after sowing can easily dislodge the tiny seeds and distribute them unevenly. The prepared mix is then gently filled into the chosen containers, leaving about a half-inch of space at the top of each cell.
Cherry tomato seeds should be sown at a shallow depth, typically about one-quarter of an inch below the soil surface. Planting deeper than this may prevent the delicate seedling from reaching the light and expending too much energy during emergence. To ensure at least one strong plant per cell, it is standard practice to plant one to two seeds in each container.
After sowing, the seeds are lightly covered with the remaining starting mix and the container is labeled with the variety and planting date. Trays must then be placed on a heat mat or in a warm location where temperatures consistently remain between 75°F and 85°F. This warmth is necessary to break dormancy and accelerates the germination process.
Maintaining Optimal Seedling Growth
Immediately upon germination, when the first two seed leaves, known as cotyledons, emerge, the trays must be moved under a dedicated light source. Seedlings require 14 to 16 hours of intense light daily to develop strong, stocky stems. Placing the light source, ideally a fluorescent or LED grow light, just two to four inches above the plant tops prevents them from stretching excessively, a phenomenon known as etiolation.
Consistent moisture is maintained by watering from the bottom, allowing the soil to wick up water from a tray placed beneath the containers. This method encourages deeper root growth and keeps the soil surface drier, discouraging fungal growth and gnats. The ideal temperature range for active growth is slightly cooler than germination, aiming for daytime temperatures around 70°F and nighttime temperatures near 65°F.
Once the true leaves, which look distinctly different from the initial cotyledons, have developed, thinning must occur to reduce competition for resources. If two seeds germinated in one cell, the weaker seedling is carefully snipped at the soil line with small scissors, leaving the strongest, most vigorous plant to continue growing. Pulling the weaker plant out is discouraged as it can damage the roots of the remaining seedling.
If the seedlings begin to outgrow their initial containers before the outdoor planting date, they should be transplanted into slightly larger pots, such as four-inch containers. This process, known as potting up, ensures the plants have adequate space and nutrients to continue vigorous growth indoors. When transplanting, bury the stem deeper than it was previously to encourage new root development.
Hardening Off and Transplanting Outdoors
The transition from the sheltered indoor environment to the variable outdoor conditions requires a gradual process called hardening off. This acclimation period, lasting seven to ten days, introduces the seedlings to direct sunlight, wind, and cooler temperatures. Initially, plants should be placed outside in a shaded, sheltered spot for just a few hours, then brought back inside.
Each subsequent day, the exposure time is increased, and the plants are moved into brighter light and cooler conditions. This process systematically thickens the cuticle layer on the leaves and strengthens the cell walls, preparing them to withstand the rigors of the garden without severe shock. Skipping this step can result in sunscald, leaf burn, or stunted growth.
Once the threat of the last spring frost has passed and nighttime temperatures consistently remain above 50°F, the seedlings are ready for their final planting spot. Cherry tomatoes benefit from deep planting: strip off the lower leaves and bury the stem deep into the garden soil. This technique promotes a robust root system, foundational for supporting a heavy fruit load throughout the growing season.