Lettuce
Lactuca sativa
Family: Asteraceae
One of the most popular salad vegetables, letÂtuce is also used in some European countries for soup. Originating from the Middle East and the Mediterranean, many cultivars have now been developed. Those most favored in the UK may be divided by shape into three groups: loose heads of cutting lettuce, head lettuce whose leaves fold inwards, and those with long, upright, spoon-shaped leaves (romaine or cos lettuce). There is now a great range of loose-leaved lettuces on the market, most grown hydroponically. Although naturally a cool weather plant, cultivars have also been deÂveloped to grow in warm weather, and types are now available to suit all seasonal conditions. It is best to buy cultivars which are sold in your region or country as then you will be sure they are suited to your climate.
Species
Lactuca sativa is an annual with large, roundish leaves forming a close head. The erect stem grows to 1 m (3 ft) and carries small, pale yellow flowers. Seed catalogues list many cultiÂvars of lettuce. There are cultivars specially bred for summer, autumn, winter or spring cropping. In cool and cold climates winter and spring crop-ping generally takes place in a cold or slightly heated greenhouse, depending on the particuÂlar cultivar. However, there are cultivars which will stand the winter outdoors.
Cultivation
Lettuce plants can be grown in a wide range of moderately rich, well-drained soils, preferably with a pH of 6 or more. Sow seed directly into drills 30 cm (12 in) apart, then cover with 1 cm (½ in) of fine soil and keep moist. 'Chin plants to 15-30 cm (6-12 in) apart, depending on the type, and provide plenty of moisture, but avoid wetting the leaves as much as possible. If using a liquid fertilizer to encourage growth, it should be high in nitro-gen. As lettuce is quick growing, sow succesÂsively every two weeks. Start sowing in early spring and continue through summer and into early autumn, choosing cultivars suited to the sowing and cropping seasons. Bear in mind that lettuce seed will not germinate in temperÂatures above 25°C (77°F).
Climate
Zone 6. Lettuce is grown as a seasonal annual in all climates. Ideal range is 10°-20°C (50°-68°F), but not above 25°C (77°F).
