GARDENING All about lettuce

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Served in dishes for the last 4500 years, the lettuce is one of the oldest cultivated vegetables.Lettuce

ettuces in their various forms are the most important salad crops, easily available at anytime of the year since the development of varieties which can be grown under glass in winter. The heavy, crisp iceberg lettuces are more popular in America, and were developed to survive transport from California to the markets in the east. Looser, softer cabbage lettuces are more popular in Northern Europe. Cos lettuces, at their best in spring, are much grown in the eastern Mediterranean. In China, the Celtuce, a variety with swollen crisp fleshy stalks, is widely grown for use sliced and stir-fried.

ORIGIN

All lettuces were developed from the wild species Lactuca serriola L. found wild in clearings in woods, rocky slopes and waste places from Asia and North Africa to northern Europe. It is a winter annual, germinating in autumn, and forming rosettes of leaves which become very conspicuous on roadsides when they begin to flower in late summer, the stems reaching 2m in height. The leaves are often spiny and usually held in a vertical position. They are either obovate and entire, or deeply lobed. The small flowers are pale yellow, and the seeds grayish green.

HISTORY

Lettuces were grown by the Romans, but are thought to have been cultivated first by the ancient Egyptians in around 4500BC. Wall paintings in some Egyptian tombs are thought to represent a narrowly pointed form of Cos lettuce, though there are suggestions that the plant was first cultivated for the edible oil in its seeds, rather than as a salad. The wild species is horribly bitter even when young, and the selection of less bitter forms would have been one of the first actions of the early cultivators of the crop as a salad. Bitterness is associated with the production of latex, the milky juice still found in the cultivated varieties when they bolt. Lettuce as a food plant was probably introduced to Britain by the Romans, who favoured the plant after it was said to have cured the Emperor Augustus. Their varieties needed blanching to make them less bitter. The earliest post-Roman mention in Britain is in Gerard’s Herball in 1597. He mentions eight varieties. Seeds were taken to America by the early settlers. Lettuces with firm hearts are only known with certainty from the sixteenth century onwards. Modern breeding has concentrated on resistance to disease and bolting in the common types, and on more fancy leaf shapes and colours such as red and curled. As readers of Beatrix Potter will know, lettuces are soporific. This property has been recognized since ancient times, and is mentioned by Hippocrates, who was born in Cos in 456 BC. The bitter latex was often used as a substitute for opium or laudanum. Dr A. Duncan of Edinburgh studied the effects of lettuce juice, which he called “lactucarium” and in 1809 published a paper entitled An account of a method of preparing a soporific medicine from inspissated white juice of the common garden lettuce.

CULTIVATION

Lettuce requires a rich but welldrained soil, kept continually moist during the growing season. Premature drying out causes the lettuces to go to seed early, before they have developed their full size. The ideal soil is one in which manure or compost has been incorporated the previous autumn, but failing that the plants can be watered with a nitrogen rich fertilizer. Seed requires cool conditions to germinate, and may become dormant above 200C. Early spring and autumn crops are best sown in boxes indoors and then planted out a spacings suited to the variety, but late spring and summer crops are best sown in the position and then thinned. This is probably because they produce deeper root systems and are more tolerant of drought.

PEST AND DISEASE

Apart from the usual danger of slugs and snails, lettuces are particularly attacked by aphids and by cutworms. The lettuce root aphid (pemphigus bursarius) is the worst danger. The fat pale brown aphids crowd around the tap root and the plant grows poorly, goes yellowish and collapses in dry warm weather. The aphid is spread by ants, and often infects weeds such a sow thistles, several

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ornamental daisies and perennial vegetables like globe artichokes. It is thought to survive the winter on populars, where it breeds in the young leaf stalks before flying to the lettuces and other hosts in June, making the worst months for attacks June, July, August and September. Other aphids affect the leaves, and the main danger is that they can carry virus diseases. Modern breeding has produced varieties resistant to root aphid, and where root aphid has proved to be a problem, the varieties “Avoncrisp” and “Avondefiance”, or the aphis-tolerant variety “Debbie” can be grown. Some strains of wild species Lactuca virosa have provided breeders with a useful source of resistance to these aphids. Cutworms, which are the caterpillers of various moths, can also be a nuisance. They eat into the root of the lettuce at ground level, and before they have been detected, the plant collapses, and the caterpillar has moved on. They are best controlled by going out with a torch at night and searching around the base of the plants. The cutworms are brownish or greenish, fat and juicy-looking and about 2cm long. A fierce watering in early June will also kill the young caterpillers, before they have been able to do any damage. Leatherjackets, the larvae of the daddy-long-legs or cranefly, are also sometimes troublesome. They can eat the roots but seldom kill the plants outright. Various mildews may also infect lettuces. The worst is grey mould or botrytis which affects plants outdoors in exceptionally wet and humid weather, and in winter lettuce grown under glass. Downy mildew, which affects the leaves, can also be a problem especially in the autumn, but again using a resistant variety will help. And although you can spray with a fungicide it is not usually worthwhile.

Mark O’Shaughnessy