Tomato crop can be planted by in-field sowing or transplanting.
Transplanting requires growing seedlings in a seedbed, generally enclosed, to ensure temperature suitable for germination. It can be done by broadcast sowing on the seedbed, or placing single seed in containers (cell flats, biodegradable pots) or blocks of potting soil; in the first case the plants are transplanted with bare root, in the other cases together with the ball of soil.
Sowing in a seedbed guarantees various advantages: time-saving, faster growth, greater evenness, less seeds used.
Seedbed sowing is done at various periods according to the type of crop desired: autumn-begin of winter for greenhouse cultivations; winter for early maturing crops, temporarily protected; end of winter (February-March) for open air crops in full season; summer for cultivations on a late maturing cycle.
1 square metre of seedbed can produce 500-600 seedlings suitable for transplant, which are obtained from sowing 2-3 grams of seeds corresponding to 600-900 seeds per square metre. Each hectare of crop requires 60-80 square metres of seedbed, with placement density of 3500-4500 seedlings per hectare.
40-60 days after seed sowing the tomato seedlings reach the stage of having 4-5 leaves and the height of 100-150 mm: this is the best time for transplanting.
Transplant of processing tomato in open-field cultivations takes place from mid-April to mid-May. In open-field, double row planting is widely used and we will discuss it later in reference to direct seeding.
The transplant is done either by hand or with a machine; seedlings grown in cell flats with their ball of soil adapt well to the latter method.
Direct Seeding is expanding in open-field cultivation because of its benefit in reducing planting costs and yielding strong plants, especially in the root system, as they do not need to overcome the stress of transplant. Negative aspects are: higher quantities of seeds are used, the seedbed requires accurate preparation, a certain amount of thinning may be required, sowing cannot be done before the air temperature reaches the minimum level needed (about 12 °C) to ensure germination and reasonably quick sprouting.
Tomato can be sowed with extra seeds (1-1.5 Kg/ha) postponing the elimination of the plants in excess until the thinning out process; or 0.4-0.5 Kg/ha of seeds can be sowed using a precision seed driller, in which case thinning out can be omitted.
Placement of the plants, therefore the seeds, in the soil can be done in simple rows spaced at 1-1.5 m distance, but it is mostly done in double rows having 0.30-0.40 m between each rows and 1.3-1.5 m between the double row.
The double row presents various advantages:
- The leaves provide better shading for the berries;
- Less side-shoots and better simultaneous ripeness due to the strong competition among the plants in the double row;
- Lower cost for drip irrigation (quite common) due to the reduced length of driplines;
- Easier mechanical harvesting.
The investment varies from 3 plants every 2 m for simple row crops to 6-8 in case of double row.
Seeding depth cannot exceed 20-30mm given the small size of the seeds.
Use of the precision seed driller with pelleted seeds favours uniform sowing, as the seeds’ rough surface otherwise would tend to make them stick together.
Open-field tomato seeding is done in the spring: towards March in more mild Southern regions, and in April in the Central-Northern regions.
Transplanting always needs additional irrigation to ensure rooting. After seeding, soil rolling can enhance seeds moisture and germination.
Hoeing is recommended not only to control weeds, but also to air the soil and reduce evaporation.
In many cases, mulching with black plastic film is practised: in general associated with double row planting and drip irrigation. The dripline is placed at the centre of the double row, below the mulch sheeting. High costs are offset by great advantages in terms of agronomics and quality (clean products).
Installation of supports is needed for the greenhouse varieties or other open-air varieties (San Marzano) having undetermined growth. For these varieties certain special operations are performed, such as: pruning to eliminate axillary shoots and keep a single stem plant; topping, i.e. trimming the plant by leaving 3-6 trusses to enhance maturation of the fruit on the trusses left in place; treatments with growth regulators that in greenhouse cultivations favour fruit set and development of parthenocarpic fruit.
Irrigating increases and stabilises yields even though it does not always enhance the quality of the fruits. For salad tomatoes frequent and light irrigation is preferable; whereas less frequent and more abundant irrigations are more advisable for processing tomatoes, making sure to water well in advance of the harvest. In case of limited availability of water resources, some water savings can be achieved during the vegetative phase and during ripening, but water should not be lacking during the flowering phase. Poor water management can create damages in sensitive varieties such as blossom end rot, fruit cracking and scorching.
The sprinkler irrigation method is not free from drawbacks (it promotes fungal diseases and bacterial canker); the lateral infiltration method is one of the most frequently used, and drip irrigation is more and more used: both methods have the advantage of not wetting the plants.