CULTIVATION STRATEGY FOR
Lettuce is a vegetable that requires minimal care and is almost unaffected by pests, so it is considered very easy to grow. As it has a short production cycle, it can be planted together with other longer-cycle vegetables to make better use of space. Moreover, there are many varieties of this vegetable and by combining them it is possible to have a harvest all year round.
In recent years, lettuce cultivation has gained a lot of importance, both due to the large variety of lettuce types available and the increasing consumption of convenience foods. Pre-prepared convenience foods are vegetables that have undergone minimal processing (washing, chopping and packaging) and are ready to eat.
When planting lettuces, it is best to plant them on ridges or benches, at a height of about 25 cm, so that they do not come into direct contact with humidity and thus avoid diseases and rotting of the lettuce neck. However, we must also take into account a series of factors such as the following:
Generally, lettuces prefer light, sandy-loamy, nutrient-rich and well-drained soils. If planted in nutrient-poor soil, the addition of well-decomposed compost is recommended. The optimum soil pH for this plant should be between 6.7 and 7.4. It is also a drought-sensitive crop, but special care must be taken to keep the soil surface dry, otherwise lettuce neck rot may develop.
Lettuce prefers different soils depending on the variety to be sown:
- Spring varieties: sandy soils, as it warms up faster and harvests are earlier.
- Summer varieties: soils rich in organic matter, thus allowing a better use of water resources.
- Autumn varieties: loamy soils, as they cool down more slowly.
Lettuce adapts well to almost all climates, as it withstands a very wide temperature range (from -6oC to 30oC). However, below 6oC, growth is stunted, so in cold areas it is necessary to cover crops with protective plastic sheeting.
»Care requirements for lettuce
For lettuce cultivation, seeds are sown in seedbeds for 30-40 days. Once the plants are about 8 cm high and have 5-6 leaves, they are ready to be transplanted into the garden.
·Soil conditioning for lettuce cultivation
First of all, it is important to level the soil to prevent waterlogging, which is harmful to the lettuces. In addition, the necessary ridgeswill be formed on which the plants will be planted later.
Another characteristic of this crop is that it is recommended to grow it after legumes, cereals or fallow and not after crucifers or composites.
On the other hand, it is important to note that this is a short-cycle crop and very sensitive to chemicals, so chemical disinfection of the soil is not recommended (solarisation in summer is recommended).
Finally, during the winter, padding with black or transparent polyethylene sheeting is recommended. These sheets are also used with small lettuces and lettuces that do not form heads and whose leaves remain wide open, thus preventing them from getting dirty with soil.
For lettuce cultivation it is very important to control soil moisture and avoid waterlogging. Watering should therefore be frequent, but not very abundant.
Drip irrigation (in greenhouses) and drip tapes (outdoors) are the best irrigation systems for this type of crop because of their constant water transmission, but without waterlogging problems.
On long-leaved lettuces, such as Romana, blanching techniques are used. They consist of tying the leaves with a rubber band 5 to 7 days before harvesting. This is intended to make the inner leaves as white as possible instead of the typical dark green colour.
It is very important to eliminate weeds in lettuce crops, as they can create an environment conducive to the development of diseases.
»Fertilisers for lettuce cultivation
Leafy greens have basic nutritional needs, so they are easy to grow.
Lettuce, in particular, needs nitrogen to ensure productive leaf growth. Potassium and phosphate are also important nutrients for this crop. However, excessive fertilisation, especially nitrogen fertilisation, must be avoided in order to prevent possible phytotoxicity due to excess salts and to achieve quality leaves and ideal bud formation. Therefore, balanced fertilisers with equal parts of nitrogen, potassium and phosphate shall be applied.
With regard to potassium fertilisation, the supply of this element must be controlled, especially in cold periods, but it is also important to bear in mind that lettuces will absorb more magnesium as they consume more potassium. This will therefore have to be taken into account when balancing this potential shortfall.
On the other hand, the crop is quite demanding in terms of molybdenum during the early stages of development. The application of this element, both preventively and for the correction of possible deficiencies, is recommended via foliar application.
If organic lettuce cultivation is desired, compost, rotted manure, fish emulsions, etc. can be mixed into the soil before planting. This will give the plants the nutrients they need to maximise production.
Lettuce maturity is measured by the degree of compactness of the heads. A head is considered to be compact and therefore ready to be harvested when moderate manual force is required to compress it (without being extremely hard).