OUR humble lettuce, Lactuca sativa is now so diverse, that it is difficult to imagine a clump of wild lettuce growing on a rocky hillside in the Mediterranean.
In their natural, wild forms, the various species of lettuce contain high levels of a narcotic drug called lactucarium that was known as lettuce opium.
It was in fact used as a sedative in the 18th century.
Lactuca serriola, L. canadensis and L.virosa are the main sources of this compound, made from the dried latex that exudes from the cut leaves.
It is from this that the plant gets its scientific name – lac is Latin for milk – the milky sap.
Enough of the science and history lessons – what about our modern lettuce in all its strange and diverse forms (its level of lactucarium are too low to consider).
Over recent years, we have seen a huge increase in the range of lettuces available to us – both in supermarkets and through our seed catalogues – with colour, texture and flavour varying considerably from one type to another.
There are six main groups to select from.
Broadly they are split into those that form a distinct heart and those that do not: Butterhead, much favoured on the continent, Chinese lettuce (sometimes labelled as Chinese cabbage), mini lettuce varieties, Crisphead or Iceberg types, leafy types and Cos or Romaine types.
In addition, seed suppliers are now selling mixed lettuce leaf packs that are ideal for pot culture.
These can be pulled as young plants, trimmed, washed and eaten in seconds, along with all the other salad leaf crops now available.
Due to the lettuce’s wild origins in poor, rocky and thin soils, it germinates and grows best in cooler climates and does not like very hot, dry conditions in which it tends to run to seed (bolting) very quickly.
It is only at this stage that you realise that lettuce belongs to the daisy family, Asteraceae (syn Compositae).
The growing of early and quick maturing varieties is therefore best and the use of successional sowings to get a continuous supply of young leaves is probably the best way to grow them.
There are one or two cultivars that can be over-wintered in polythene tunnels, cool glasshouses and even in cold frames if you want lettuce all year round.
Look out for Lobjoit’s Green Cos, Tom Thumb, Valdor and Clarion.
One of the nice developments over recent years is the red-leaved cultivars that add colour as well as flavour to a salad and they are often slug-resistant.
Look out for Lollo Rossa, Sioux, Giardina, Sangria, Sierra and Babylon.
The growing of lettuces has been experimented with by every gardener who ever existed but, to ensure a good start, the best way is to sow thinly in seed trays or cellular trays under glass.
Only transplant to their intended plot once they have reached the five or six true leaf stage.
Direct sowing outdoors exposes the germinating seedlings to slugs, pigeons, mice and bad weather and leaves you with a delayed start.
Whichever lettuce you intend to grow this summer, enjoy their crisp texture and slightly bitter flavour but do not expect any effects from the lactucarium.
Their Vitamins A and E, folic acid and the anti-oxidant benefits should be enough.