Synonym for Lettuce is Lactuca sativa L.
Common names are Endive, Escarolle (Eng.); Chicore Frisde (Fr.); Escarola (Sp.); Krause Winter Endivie (Ger.); Krulandijvie (Neth.).
Cultivars are in India.
The Middle East, later spreading to Egypt by 4500 BC, Greece and many parts of the Mediterranean before being introduced to China by the seventh century AD. A recent introduction to the tropics. Possibly derived from L. serriola L. which is indigenous to western Asia.
Cultivated to a limited extent in the Caribbean, Malaysia, East and West Africa, mainly at high altitudes.
A perennial herb with fleshy rootstock, up to 2 m in height. Normally grown as an annual. Roots: fibrous. Tubers: formed from underground stolons; oval, irregular, skin colour red, purple or white; contain carbohydrate in the form of inulin which, on hydrolysis, forms fructose. Stems: hirsute, often grooved. Leaves: opposite or spirally arranged, simple, hirsute, 10-20 cm in length. Flowers: in large capitula, borne on flowering stems up to 2 m, 4-8 cm in diameter; bracts herbaceous; receptacle flat or conical; ray florets sterile, normally yellow; disc florets hermaphrodite, tubular, yellow, purple or brown.
Relatively tolerant to a wide range of climatic and soil conditions although well-drained sandy loams, with a pH of 6.0-6.8 are generally considered preferable. Cultivars which are specifically adapted to tropical environments have been hybridised or selected for many ecological regions. Many are tolerant to high day temperatures of up to 30C and short days, although the most suitable range for most cultivars is 15-20C. High temperatures often result in premature flowering, stunted leaf growth and bitter tasting leaves. At low elevations in high temperature areas, some cultivars do not form solid heads; they tend to flower precociously and seed without forming the normal number of rosette leaves. Cultivars have been selected which do not readily form flowering stems at high temperatures. Elevations above 1000 m provide good conditions for optimum growth. Seeds require a period of dry storage before sowing and some cultivars which have been stored at high temperatures have a requirement for exposure to light before dormancy is broken. The optimum germination temperature is 25C; above this temperature, germination percentage falls rapidly due to an inhibition of gaseous diffusion and a consequent shortage of oxygen. Gibberellic acid (GA3) has been found to overcome dormancy induced by high temperatures. Viability is rapidly lost in moist atmospheres at high temperatures. Daylength variation does not appear to affect development to any significant extent.
Propagation is by tubers; the size of the tuber planted is often related directly to the yield. Tubers, or portions of tuber (setts) with 2-3 buds, weighing approximately 56 g, are planted at a depth of 2.5-5 cm, usually on 300-500 kg/ha of tubers or setts are required. Beds are often mulched directly after planting to conserve soil moisture and plants are sometimes earthed up when tuber development begins. Supplementary applications of both nitrogen and potassium are likely to be required since the crop demand for these minerals is relatively high.
Plants normally mature within 70-85 days from transplanting, depending on factors such as soil fertility and irrigation efficiency. Yield: Yields in the region of 6-12 t/ha may be obtained. Seed production: Seed is rarely formed in the tropics, except at elevations above 1500 m. Most cultivars are almost completely self-pollinated. A 600 m isolation distance is sufficient unless hybrid seed is being produced, when 1000 m is more appropriate. The average seed yield is 200 kg/ha.
The leaves should be fresh and crisp, free of diseases or pests and either green or cream, if blanched. The central leaves should be healthy, with no discoloration. The heads are normally washed immediately after harvest. Wilting can be reduced by spraying with water but complete enclosure within plastic wrappers or bags should be avoided, the top should be left open. At 0C the storage life is about 20 days.
Normally used in the raw state in salads but also as a cooked vegetable, particularly in Southeast Asia. Loose-headed forms have a higher vitamin A content than heading cultivars.
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