Tomato care measures in greenhouses

15.07.2026

Masat e përkujdesit ndaj domateve në serra

Pollination and fruit setting – When we have good climatic conditions, tomato self-pollination is satisfactory and does not require human intervention. However, at low temperatures and high air humidity, as well as at high temperatures, self-pollination of plants becomes difficult, which consequently results in poor fruit set. To improve fruiting, producers usually treat flowers with chemical formulas containing auxins. However, due to unprofessional use, this technique often results in low-quality fruits (voids, pale color, sensitivity to botrytis, etc.). Another part of the producers try to improve pollination by applying plant vibrations/oscillations. However, there is no doubt that the best results come from using pollinating beetles (Bombus terresris), which are very efficient in pollinating flowers. For their maximum activity, greenhouse conditions need to be within normal limits, and usually colonies with beetles are placed in the shade of plants inside the greenhouse so that they do not expend too much energy maintaining the required temperature inside the hive. A normal hive covers 2000-2500 m² of tomatoes, while the lifespan of a hive is 8-12 weeks, depending on the climate and pesticides used in the greenhouse.

Watering - It is one of the most important services for tomatoes in the greenhouse. Plants react relatively quickly to a lack or excess of water, while symptoms are easily noticed, which facilitates intervention. Before entering the drying phase, plants lacking water take on a dark green color and become firm. In contrast, plants that have a lot of water in the root zone have a lighter than normal green color and partially yellowing of their lower leaves, which is a consequence of their inability to absorb nitrogen from the soil.

It has been calculated that for a tomato plant (90 cm tall) with a fully developed leaf mass, during the fruiting phase (excluding water loss in the soil), depending on external climatic conditions, the water doses required are as shown in the following table.

Climatic conditions	Amount of water per plant (liter)
Time with lots of clouds	0.14-0.28
Cloudy for most of the day	0.28-0.42
With relative clouds	0.71-0.85
Sunny with slight variations	1.1-1.2
With sunshine	1.5-1.8

For a 22-week vegetation period (with a weekly requirement of 9 liters), it can be estimated that one plant needs about 200 liters of water.

Simply put, tomato watering should be organized as follows:

a) After preparing the soil for planting, the soil should be irrigated until it is fully capable of being fielded.

b) After transplanting the seedlings, watering is done for occupation. After this, a dry period must be ensured, the length of which will depend on the cultivation cycle, soil conditions, etc., and continues until the first and second blooms have well formed and become visible

the third and fourth blooms.

c) After this, the required amounts of water are given at regular intervals until the end of production. Their frequency should depend on the climate, soil, development stage, and method.

d) Under no circumstances is plant wilting allowed.

Nutrition - To ensure high and quality productivity, it is necessary that plants have sufficient amounts of nutrients around the root zone, which are easily utilized. Tomatoes respond differently to a number of nutrients, but depending on their dose, the plant exhibits different behaviors related to vegetation/reproduction ratio, the speed of transition through different phenological stages, susceptibility to diseases and pests, or the speed of onset of various physiological disorders.

Reaction to nitrogen - As nitrogen doses increase, plant vitality usually also improves, such as their height, number of leaves, and the number of flowers formed. Similarly, plant production increases in parallel with the increase in nitrogen doses, as they remain at moderate levels. However, very high doses of nitrogen reduce the production achieved by plants. It is clear that plants' reaction to nitrogen does not depend only on the dose at which it is used, but also on the nitrogen content in the soil and the intensity of its mobilization, mineralization, or denitrification during the plant's life cycle.

Reaction to phosphorus - Phosphorus deficiency limits the growth and development of plants, but at the same time reduces the number of flower buds formed and delays their flowering. Meanwhile, high doses of phosphorus can limit plant production and increase the quantity of ripe fruits unevenly or those with gaps.

Reaction to potassium - Plants grown in environments with insufficient potassium levels produce fruits of poor quality, with voids, deformities, and poor taste, all due to the lack of organic acids. Increasing potassium nutrition improves all the quality components of the fruits, as well as their shape and stability.

Reaction to calcium and magnesium - Calcium deficiency reduces plant height and the number of formed leaves, while magnesium deficiency decreases plant growth and production. Adding magnesium to the soil improves the shape and quality of the fruits. Meanwhile, magnesium deficiency is one of the most common nutritional disorders in tomatoes. This phenomenon occurs most often under conditions of abundant nitrogen and potassium fertilization. For example, production losses due to magnesium deficiency can reach 5% under low-dose nitrogen fertilization but increase up to 10% if nitrogen doses are high.

Tomato fertilization techniques in greenhouses - To determine the plants' fertilizer needs, soil analyses are first conducted, which are taken at least once a year before the base fertilization. Meanwhile, particular importance in determining the daily fertilization doses is knowing the daily rates of assimilation of key nutrients by the plants, as this fact allows for determining the daily doses of fertilizers to be used to supplement them, as well as the ratios between the main nutrient elements at different stages of plant development. Tomato fertilization in greenhouses is carried out through the following fertilization methods: a) Basic fertilization, companion fertilization, and supplementary fertilization.

a) Basic fertilization of plants - It is done with organic and mineral fertilizers, aiming for the soil at the time of planting to have a pH of 6-6.5, sufficient phosphorus reserves throughout the entire growth cycle, a sufficient amount of nitrogen for the first growth phase but not in excess, as it stimulates excessive plant growth. Also, this fertilization ensures sufficient potassium reserves, which guarantee good fruit quality in the early stages of production.

The amount of fertilizers that can be used in base fertilization depends on the fertility of the soil. The distribution of base fertilizers is carried out before soil tillage (organic fertilizers and some of those containing phosphorus and potassium) and before the final preparatory tillage of the planting bed. With the latter, pesticides necessary for disinfecting the soil from fungal diseases, or for controlling soil insects and nematodes can also be applied.

The following table presents the indicative fertilization rate for the basic tomato fertilization:

Soil fertility level	Recommended amounts (kg active ingredient/100 m²)
Soil fertility level	N	P	K	mg
Low	3.5	2.5	5.5	2.8
Average	2.8	1.5	4.4	2.0
High	2.0	0.5	3.2	1.2
Very high	1.2	0	1.9	0.4

b) Companion fertilizations - These aim to promote the rapid adhesion of plants to the soil and its rapid growth immediately after planting in their permanent location. These fertilizers are carried out shortly before planting the seedlings in their permanent location or alongside their planting. Companion fertilizations are usually done through nutrient solutions poor in nitrogen and potassium, but rich in phosphorus. Their purpose is to stimulate the immediate activation of the root system and the quick attachment of plants to the soil. Such fertilizers are necessary in early plantings when, due to low soil temperatures, the rate of phosphorus assimilation from the plants' root system is very low.

c) Supplementary fertilizations - They should be such that they ensure the establishment and maintenance of normal relationships between the vegetative and reproductive growth of the plants. When determining fertilizer dosages, it should be taken into account that plants' requirements for certain nutrients vary at different stages of their phenology. Plant requirements increase in parallel with their growth, thus reaching their peak during the intensive fruit growth phase. This phase should also correspond to the maximum doses of supplementary fertilizers. Rigorous tomato fertilization must respect: 1) the biological requirements of the plants during their specific biological periods, 2) the projected yield, 3) the state of soil fertility, 4) the utilization coefficients of nutrients from the soil and fertilizers, etc.

The following table presents the indicative rates for supplementary fertilization of tomatoes in greenhouses, expressed in kg/day/1000 m²:

Phenological phase	N	P₂O₅	_K2O
Transplanting - the first flower	0.10	0.10	0.10
The first flower - flower formation 5	0.20-0.40	0.12-0.24	0.30-0.50
The fifth flower - the beginning of the harvest	0.50-0.80	0.30-0.50	0.75-1.20
Harvest period	0.60-0.80	0.40-0.45	0.90-1.20
6 weeks before the last harvest	0.20-0.30	0.12-0.18	0.30-0.45

Another very important element in tomato fertilization is respecting the requirements for optimal ratios between the basic elements, phosphorus nitrogen and potassium, in accordance with the phenological stages of the plants. These ratios vary from 1:2:1 immediately after transplanting to 1:1:1 during the vegetative growth phase of the plants, and 2:1:3-4 during intensive fruit growth and ripening.

The garbage is dispersed along with the water in two different ways:

1) Quantitative methods and

2) The proportional method.

With the quantitative method, fertilizers are mixed with irrigation water, using a 'by-after' tank for this purpose. In this case, the factor controlling tomato growers is the total amount of fertilizer used. The recommended amounts of fertilizers with this method are 2-5 kg/ha/day in the first 2-3 weeks after plant transplantation and 10-20 kg/ha/day during the intensive growth and fruiting phase.

With the proportional method, the concentration of fertilizers in the nutrient solution is adjusted throughout the entire fertilization period. In this case, venturi injectors or hydraulic pumps are used to mix fertilizers with water. The proportional method allows full control of fertilizer concentration in the soil, making it highly recommended in light and sandy soils, poor soils with low absorption capacity. The recommended concentrations of fertilizers with this method are 0.1-0.2 g/liter in the first weeks after transplantation and 0.3-0.5 g/liter during the later stages. If fertilization is applied once every 2 or 3 waterings, the fertilizer concentration increases by the same amount, but with continuous attention paid to avoiding salinization in the soil.

Harvesting tomato fruits - The ripening time of tomato fruits mainly depends on the air temperature and the position on the rooster. Raising the air temperature (within optimal limits) accelerates the ripening of the tomato. Fruits in the last flowering position have a longer growing period than the first fruits. The average growth period of tomato fruits is 45-60 days.

Considering the distance of the market where the production is planned to be offered, it is necessary to determine the harvest time so that the fruits reach their final destination in full touch, with an attractive appearance and the best possible quality.

Harvesting should be done during dry and cool weather, after dew or before evening. After sunset, harvesting should be avoided, but also during rainy periods, because the fruits will absorb moisture, which spoils more easily. Fruits and other plant parts must not be damaged during harvesting (damaged products spoil quickly, rot, and pose a risk to healthy crops they come into contact with), and quick and convenient transport to the warehouse or collection station must be ensured, where in case of prolonged storage, the produce must be placed under ventilation conditions, dark and cold conditions, and similar conditions.

Optimal conditions for storing/preserving tomato fruits for 3-4 weeks, in the refrigerator and cooling environments, should ensure a temperature of -1 to +1 ^°C and relative air humidity of 90%.

It should be mentioned that vegetable fruits continue their vital functions even after harvesting (respiration, ripening), so due to the loss of heat and water, drying, wilting, rotting, changes in taste, aroma, and color occur. These factors must be taken into account when planning transport and the contracted quantity that must reach the market.

During the sorting and packaging of fresh vegetables, the main principles can be the general rules for placing vegetables into circulation (marketing), which require these six (6) main conditions to be met: 1) the vegetable fruits must be ripe and fresh, 2) they must not be contaminated, 3) they must not be wet or rotten, 4) they must not contain residues from plant protection products in amounts that could be harmful to health, 5) they must not have an unknown and indetectable smell or taste and must not contain mechanical mixtures, 6) they must not have cracks, holes, insect damage, diseases, freezing, or other mechanical damages, nor other deficiencies that could worsen quality