Roma tomatoes, often called paste or plum tomatoes, are favored by home gardeners for their dense, meaty flesh and low water content, making them perfect for sauces and canning. Successfully growing these productive plants begins with seed starting, which requires careful attention to initial planting density to ensure healthy plant establishment. Understanding the proper initial setup is the first step toward a bountiful harvest.
The Optimal Number of Seeds
Planting a single Roma tomato seed per spot is risky due to the inherent unpredictability of germination success. The standard practice for ensuring a successful start is to sow two or three seeds in each hole or seed cell. This slight overplanting accounts for seeds that may not be viable, which is common even with fresh, high-quality stock. This approach is standard across many small vegetable varieties to guarantee a high rate of successful emergence.
The goal is to select the strongest seedling from the group and discard the rest, aiming for one final plant per intended location. You should aim to place these seeds in a small depression, typically a quarter-inch deep. By planting two or three seeds, you create a built-in redundancy that maximizes the chance of at least one strong seedling emerging in every spot.
Understanding Germination and Why We Thin
The reason for planting multiple seeds is related to typical germination rates, which hover around 75 to 80 percent for many commercial varieties. Using two or three seeds per cell guarantees that the container will not be left empty, which saves time and resources for the gardener. Once the seeds sprout and the initial cotyledon leaves emerge, the process of selection and thinning must begin to prevent competition for light and nutrients. This step is performed when the tiny seedlings have developed their first set of true leaves.
Allowing all seedlings to grow past this point will stunt their development, as the roots will begin to fight for limited space and moisture below the surface. The correct method for thinning is to select the single, most robust seedling and carefully snip the others at the soil line using a small pair of scissors. It is important to snip rather than pull the unwanted seedlings, because pulling risks disturbing the fragile, intermingled root system of the chosen keeper plant. This action eliminates competition, allowing the single strongest plant to allocate all available energy toward healthy, unhindered growth.
Preparing the Seed Starting Environment
Before sowing, preparing the correct environment ensures the best chance of germination. A sterile, fine-textured seed-starting mix is preferred over heavier garden soil, as it provides a clean medium that prevents disease and offers superior drainage. The seeds should be placed about one-quarter inch below the surface of this mix, a shallow depth that allows the seedlings to emerge without expending too much stored energy. Maintaining a warm soil temperature encourages rapid and uniform sprouting.
The ideal temperature range for tomato seed germination is consistently around 75 to 85 degrees Fahrenheit, which often requires supplemental heat indoors. A specialized heat mat placed under the seed tray can help regulate this temperature and accelerate the process, which usually takes between five and ten days under optimal conditions. Starting the seeds indoors, typically six weeks before the last frost date, gives the young plants a substantial head start.
Transitioning Seedlings to the Garden
The successful, thinned seedling must be gradually prepared for the outdoor world through a process known as “hardening off.” This involves slowly introducing the plant to increasing periods of direct sunlight, wind, and cooler nighttime temperatures over a period of seven to ten days to prevent transplant shock. This acclimation strengthens the plant’s cell structure and thickens the stem. Once the threat of frost has passed and the garden soil temperature is reliably above 60 degrees Fahrenheit, the seedling is ready for its final location.
Roma tomatoes, which are generally determinate varieties, require a final in-ground spacing of 18 to 24 inches between plants to ensure proper air circulation and resource availability. When placing the plant into the garden soil, bury the stem deeply, up to the lowest set of true leaves, because tomatoes readily develop new roots along the buried portion of the stem. Due to the heavy, concentrated fruit production typical of Romas, installing a sturdy cage or stake at the time of planting is recommended to support the weight and keep the fruit off the soil.