Tomato requires a relatively cool, dry climate for high yield and pre-mium quality. However, it is adapted to a wide range of climatic con-ditions from temperate to hot and humid tropical. The optimum tem-perature for most varieties lies between 21 and 24 °C. The plants can survive a range of temperatures, but the plant tissues are damaged be-low 10 °C and above 38 °C.
Tomato plants react to temperature variation during the growth cycle (see Table 1), for seed germination, seedling growth, flower and fruit set and fruit quality. If cool or hot weather spells persist during flower-ing, pollen production will be low. This will influence fruit formation. Frost will kill the plants. To avoid frost damage, it is best to wait until the winter is definitely over before sowing. It is possible to sow in-doors earlier (in pots or trays). Light intensity affects the colour of the leaves, fruit set and fruit colour.
In tropical lowlands, the minimum temperature at night is also important. Temperatures below 21 °C can cause fruit abortion.
Temperature requirements for different stages of tomato
|Stages||Temperature (° C)|
|Red colour development||10||20-24||30|
Water and humidity
A simple rule of thumb can be used to determine whether local water supplies are sufficient for growing tomato. If there are herbaceous plants (plants with many thin leaves) growing in the natural environ-ment, it will be possible to grow tomato. You should be able to count on at least three months of rain. Water stress and long dry periods will cause buds and flowers to drop off, and the fruits to split. However, if rains are too heavy and humidity is too high, the growth of mould will increase and the fruit will rot. Cloudy skies will slow down the ripen-ing of tomatoes. However, adapted cultivars are available. Seed com-panies have special tomato varieties for hot-humid climates.
Tomato grows well on most mineral soils that have proper water holding capacity and aeration, and are free of salt. It prefers deep, well-drained, sandy loam soils. The upper layer needs to be permeable. Soil depth of 15 to 20 cm is needed to grow a healthy crop. In heavy clay soils, deep ploughing allows better root penetration.
Tomato is moderately tolerant to a wide range of pH (level of acidity), but grows well in soils with a pH of 5.5 – 6.8 with adequate nutrient supply and availability. Addition of organic matter is, in general, favourable for good growth. Soils with very high organic matter content, like peat soils, are less suitable due to their high water holding capacity and nutrient deficiencies
Tomatoes are very sensitive to water logging and soil borne diseases and pests. It is therefore
necessary to test your soil first before planting. Check the following when you test:
- Soil type
- Presence or absence of soil borne pests and diseases.
Which variety to choose depends on local conditions and the purpose of growing . Local varieties and improved (or commercial) varieties can be distinguished. They are the result of a continuous process of selection of plants. Selection criteria are based on characteristics such as type of fruit, shape of plant, vitality and resistance to pests and diseases, but also on factors related to climate and management. Farmers in Kenya select varieties that perform best under the local conditions. Only fruits from the best plants must be selected and
Tomato breeding companies in Kenya have produced F1-hybrids. These grow from seeds that have been produced by controlled hand pollination of male and female parent lines. These hybrids combine high yield, disease resistance and other plant and fruit characteristics. When using hybrids, new seeds should be purchased each season. This may cost more money, but the resistance against diseases of hybrids means the tomato plants need less spraying with pesticides. The yields are also higher, creating more opportunity to bring tomatoes to the market.
Resistant varieties have an in-built resistance, which is carried in the seed. Resistance to a specific disease means that it is very difficult or impossible for a plant with this resistant characteristic to get that particular disease. Resistance can be a result of various plant characteristics. Leaves can be densely covered with hairs so that certain insects do not like sitting on them. Some colours can be unattractive to certain insects. Such characteristics are visible. Most characteristics that contribute to resistance to fungal and virus resistance cannot be seen. There are no varieties on the market that are resistant to all existing diseases and pests, but you can buy seed from plants that are resistant to one or several diseases.