Seedlings can be grown in seedbeds or containers, with container cultivation being more popular due to its numerous advantages.
Advantages of Container-Grown Seedlings
Seedlings grown in containers have a uniform and consistent growing space, which ensures even plant growth and high uniformity of the seedlings.
Ready-made substrates with good water-air balance, high water retention, and sufficient nutrients for complete seedling development are used for growing seedlings. These substrates are sterilized and free of pathogens, pests, and weed seeds, which are often present in natural soil.
Transplanting is facilitated with the substrate adhering to the roots, which the well-developed seedlings completely fill. Transplanting seedlings with a clump of substrate minimizes transplant shock compared to bare-root seedlings, allowing continuous growth. These seedlings establish more quickly and easily, reducing the need for replanting. Unlike bare-root seedlings, container-grown seedlings can be transplanted even into soil that is not at optimal moisture levels, and planting can be done throughout the day, allowing for better utilization of existing planting equipment and planting on larger areas within the optimal time frame.
Container-grown seedlings mature earlier for harvesting and generally yield more than bare-root seedlings grown in seedbeds.
The container method is especially suitable for producing hybrid vegetables, where it is crucial to obtain a high-quality seedling from each seed due to the high cost of seeds.
Ready-made substrates with good water-air balance, high water retention, and sufficient nutrients for complete seedling development are used for sowing in containers. These substrates are sterilized and free of pathogens, pests, and weed seeds.
Sowing can be done manually or with a pneumatic seeder.
Tomatoes are typically transplanted after developing the first true leaf, which is why they are sown densely in seedbeds or boxes without partitions, or in containers designed for sowing plants to be transplanted later. Such containers, measuring 60 x 40 cm, have 400 – 450 planting cells. Seedlings from these cells are transplanted with clumps of substrate, ensuring a 100% survival rate and speeding up and simplifying the process compared to transplanting seedlings from seedbeds or boxes. Mechanized transplanting of seedlings from small cells is also possible.
Transplanting young seedlings (pricking out) is done when the first true leaf appears. Pricking out involves transplanting seedlings from smaller cells into larger ones (35 – 50 cm³). During this process, poorly developed or damaged plants are removed, optimizing the use of growing space by filling all planting cells with healthy plants.
Pricked seedlings are of higher quality, enter the generative phase earlier, and typically produce larger fruits, resulting in higher yields. Pricking out can be done manually or mechanically, but in both cases, the substrate must be optimally moistened to prevent damage to the seedlings during transplanting.
Microclimatic Conditions for Growing Seedlings
To ensure rapid seed germination, containers are placed in germination chambers where optimal temperatures (around 30°C) are maintained, along with complete air saturation using micro-sprinklers that create a mist.
Containers remain in the germination chambers for several days until the seeds germinate. They are then moved to heated protected spaces where a consistent optimal temperature is maintained day and night until the seeds have fully sprouted, with careful management of substrate moisture.
Once the young seedlings have sprouted and developed their first cotyledon leaves, the temperature in the protected space should be reduced to 20-25°C, with nighttime temperatures about 7°C lower than daytime, accompanied by regular ventilation and substrate moisture management.
This temperature regime, with ventilation and active airflow, is maintained until the seedlings develop 6-8 leaves and a visible flower cluster, indicating readiness for transplanting. If temperatures are too high after germination, the resulting seedlings may be elongated and fragile, with lower quality and productivity.
If adverse external conditions delay planting (e.g., low temperatures, overly wet soil, rain), seedlings can be stored for up to 2 weeks at temperatures between 1 – 2°C.
Seedling Cultivation and Care Before Planting
In protected spaces, containers should be elevated slightly off the ground, using bricks or stone blocks to support wire mesh or wooden slats.
This raised position allows for faster and better heating, while the air space beneath the containers prevents root growth through the drainage holes, ensuring the roots fully permeate the substrate, facilitating easier extraction during transplanting.
The substrate should be kept moderately moist throughout the seedling growth period. Due to the relatively small volume of the planting cells in containers, watering is essential in the morning, with humidity maintained throughout the day by misting. It is preferable that the plants remain dry in the evening and overnight.
For watering, it is best to use rainwater collected from buildings, water from private wells, or clean water from natural watercourses. Direct watering with tap water is not ideal as it is generally much colder, which can negatively affect seedling development. Seedling watering is done using automatic sprinkler systems with fine nozzles that create extremely fine droplets, preventing damage to young plants and avoiding soil compaction. If watering is done manually, watering cans with fine roses should be used. Automatic watering systems can also apply foliar fertilizers such as Fertina P, Profert Mara, Kristalon, and others. Foliar feeding is used when seedlings show signs of losing their dark green color, often occurring when seedlings must remain in containers longer than optimal due to delayed transplanting.
Using quality treated seeds and growing in sterilized substrates generally negates the need for disease protection in container-grown seedlings.
However, before transplanting, it is advisable to treat the seedlings preventively with a contact fungicide such as mancozeb at a concentration of 0.2%, or copper-based fungicides at a concentration of 0.2%.
A week before the planned transplanting date, protected spaces should be fully opened to expose the seedlings to direct sunlight, helping them acclimate to the full spectrum of sunlight they will encounter after transplanting into the field.
Before transplanting, the substrate should be moderately moistened to facilitate the easy extraction of seedlings with the substrate adhering to the roots. If the substrate is too wet, it may fall off the roots during planting, while if it is too dry, the plants may not establish well in the field.
