Tomatoes are valuable vegetables. They contain soluble sugars, organic acids, cellulose and pectin, proteins, fats, minerals (potassium, phosphorus, sulphur, magnesium, calcium, iron, copper, sodium), a large number of vitamins (B1, B2, B3, PP, C, A, I, H), and tomatine, an alkaloid which has phytocidal properties. The substance lycopene, which gives tomatoes their red colour, is particularly valuable. It inhibits oxidation processes in the body and neutralises harmful substances known as free radicals, which often cause oncological and cardiovascular diseases.
Varieties. Tomato hybrids differ in plant height, fruit size and colour, and ripening time. Indeterminate hybrids are tall, with unlimited growth. The first cluster forms above leaf 8-11, with a new inflorescence forming every three leaves. The most popular varieties are ‘Isabel F1’, ‘Rondelo F1’, ‘Erophily F1’, ‘Admiro F1’ and ‘Brooklyn F1’. They are best suited for growing in heated greenhouses. Determinate hybrids are limited in growth and usually have 4-6 or more flower clusters that are ready to grow. The first cluster forms above leaf 6-8, with new inflorescences forming every 1-2 leaves. The most popular varieties are ‘Magnus F1’, ‘Platus F1’, ‘Vulkanus F1’, ‘Celzus F1’. They are best grown in unheated polytunnels and glass greenhouses in peat substrate. Foreign seed companies sell heat-treated and chemically treated tomato seeds. Seed packaging indicates the letter initials showing the disease resistance.
Sowing. Tomatoes have a long growing season, so seedlings are grown in heated greenhouses and grow in 50-70 days from sowing. The timing of sowing depends on when the seedlings are to be planted in heated or springtime unheated greenhouses.
Tomato seeds are best sown on a clean, loose, high-quality, organically certified peat, fine-textured (0-5 mm) sowing substrate (pH 5.5-6.5; EC-1.2-1.8 mS/cm), with the right (optimum) levels of macro- and trace elements. Before sowing tomato seeds, the substrate must be aerated and additionally moistened. Plastic boxes or nurseries are disinfected with a 0.2 % (20 ml in 10 l of water) Previcur solution and then filled with the prepared substrate for sowing. The surface of the peat substrate is smoothed and lightly tamped down. Then, every 3 cm, grooves 1 cm deep are made in which to place the seeds and, after placing the seeds, a 3 mm layer of peat is applied. The use of this peat substrate for sowing ensures optimum conditions for germination and seedling production, which influence the quality of the seedlings and the future yield. The use of garden soil is not recommended, because there is a high probability of introducing pathogens and substances harmful to plants.
Seeds germinate at 24-28 °C in 4-6 days. Once the seedlings have emerged, any agro textile should be removed and the boxes should be moved for 3-4 days to a place as bright and cool as possible, where the temperature is between 12-15 °C during the day and 8-10 °C at night, in order to allow the roots of the plants to better develop. The optimum air temperature for tomato seedlings during growth is 20-22 °C, 15-17 °C at night, and the optimum substrate temperature is 16-18 °C.
When the seedlings have their first true leaf, they are transplanted into pots 10-12 cm in diameter with a peat substrate for sowing. They are planted deeper in the new pots than they were before. Only healthy, strong seedlings with a well-developed taproot should be transplanted. Before using the prepared peat substrate, it should be spread to aerate and be properly moistened. It is not advisable to mix compost or other garden soil into prepared peat substrates.
Growing seedlings. Tomato seedlings are grown in heated greenhouses, preferably on racks heated from below. The potted plants are placed on the racks at a density of 15 plants/m2 to prevent contact with the leaves, so that the tomato seedlings will grow sturdy, compact and not droop. The seedlings should be watered infrequently but abundantly with warm water. The peat substrate in the pot should be moist but not wet.
After 2-3 weeks, tomato seedlings should be fertilised with an additional 0.15% solution of Nutricomplex (14-11-25) complex fertiliser. At the beginning of the growth of the seedlings, the roots of the plants develop better at lower salt concentrations. Care should be taken when growing the seedlings to avoid deficiencies of individual elements. When an element is deficient, normal growth is immediately impaired. However, excessive application of fertiliser is also very harmful. The seedlings then grow with a highly developed above-ground part, with a weak root system and poorly-formed flower clusters.
Properly-grown tomato plants must be healthy, not overgrown, not drooping, with green leaves. Seedlings planted in greenhouses should have 10-12 leaves and in the outdoors should have 7-8 leaves and a welldeveloped root system. Before planting in their regular growing location, tomato seedlings should be prophylactically treated against root diseases by watering with a 0.15% solution of Previcur.