Lettuce is an annual plant with a deep root system and few branches. In the first phase of the cycle, it forms a rosette of leaves with smooth, wavy or serrated edges, which varies in consistency according to the variety. This is the organ that will be used, before the plant reaches the second part of the cycle and the bud opens, promoting the growth and flowering of the plant's floral thalamus.
In Spain, the lettuce crop occupies some 33,000 hectares with a production of approximately 930,000 tons. Of the total Spanish production, 60-70% are of head lettuce. The other 30% are from romaine lettuce. The production is distributed among various provinces, with Toledo, Barcelona, Malaga and Murcia being the main producers of romaine lettuces and Tarragona, Almería, Alicante and Murcia the main producers of head lettuce.
It prefers soils with a loamy or sandy-loam texture, which retain moisture, but without drainage problems. It is not very tolerant to the acidity of the soil, with its growth optimum between 6.7 and 7.4 pH and moderately sensitive to salinity.
The optimum temperature is highly variable and depends on the cultivar, since there are some varieties more adapted to low temperatures. It is usually sensitive to frost and drying winds. Prefers temperate and humid climates. Its optimum growth temperature is between 15 and 20ºC. A higher temperature can cause premature flowering.
Lettuce is a plant with high watering needs, specially from mid-cycle to harvest. To maintain the turgor of its leaves, it needs to avoid periods of drought.
In Spain there are many varieties of lettuce, which we can divide into 3 types and at different times of harvest. There is the Roman type, Trocadero type and Iceberg type. Of Romana lettuce, the most consumed are the long red Romana, long green Romana, blond Romana, Tordesillas, Tres ojos verde, Tres ojos blanca or Romaverde. Of Trocadero lettuce, the best known are the Trocadero white seed, Trocadero semila negra, Reina de Maando, Verpia and Ofelia. Of the Iceberg type, the varieties Coolguard, anduma, Shogun, Salinas, Grandes Lagos 118, Montemar and Montereand are especially known.
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