The wild origin of our modern lettuce, Lactuca serriola , can still be seen all over Europe and the more temperate parts of Asia. It is likely that it originated on the Mediterranean rim on rocky wasteland or woodland clearings. This ancient wild relative of the modern lettuce contains a narcotic similar to opium. The Romans took advantage of this property eating lettuce at the end of a meal to induce sleep.
In earlier times the Egyptians held a similar view of the lettuce. However as well as a hypnotic or an aid to sleep, the plant was also linked with male virility. As any vegetable gardener will know the lettuce can bolt or serge vertically upwards. This combined with a milky substance they can exude when cut could have been seen as a symbol of the male phallus ejaculating. It is thought these Egyptian plants were closely linked with the modern day cos variety and could have originated on the Turkish coast on the island of Kos.
With the vast number of lettuce varieties in existence it is near impossible to pin-point their exact origins. Certainly both the Roman and Egyptian lettuce continued to be eaten long after the two great civilisations started to decline. Many may have hybridised with the wild type serriola to make our modern for sativa .
It is certain that these ancient civilisations saw the plant as both an appetite stimulant and an aid to sleep. In ancient Greece this led to confusion whether to eat the plant at the beginning or the end of a meal. An ancient dietician known as Galen from Pergamon would eat the plant to allow restful sleep and allow him to study without 'mental 'churnings' the following day. Somewhat contrary to this 100 years and also in ancient Greece earlier Rufus of Ephesos declared the opposite claming lettuce, 'fogged the memory and prevented clear thought'.
One of the earliest records of the modern European lettuce was in a piece by Lucas van Valkenborch who showed clear depictions of modern butterhead lettuces in his piece 'Allegory of Summer'. Although it is certain that this type existed well before the artist's death in 1597.
It is advisable not to buy the pre-packed lettuce leaves that can often be found in supermarkets. This is as once they are picked, cut, washed, packaged, exposed to light and then sat on a supermarket shelf for a couple of days there is little of nutritional value in them.
A fresh picked, organic or decent shop bought lettuce however should contain good levels of plant derived Vitamin A, Vitamin C, Folic Acid (B9), and potassium. In addition it is source of iron, especially when taken with food or drink containing vitamin C such as orange juice, a source of calcium and copper.
I used to plant lettuces in situ (straight in the ground) and never had good results. The snails and slugs would always beat me to the scene and I'd be left with nice healthy lettuce stalks with no fresh leaves.
I soon found it much easier to grow them first as seedlings before replanting them into a partially shady spot of my plot or garden.
They require a temperature of around 10°C so in the UK and temperate parts of the Northern hemisphere between April and October are usually ideal. For the southern hemisphere in warmer places such as Australia and South Africa they generally grow well but can have a tendency to bolt. It is perhaps better to invest in bolt resistant varieties in these countries or plant them in partial shade.
To avoid a glut you can space the seedlings out by sowing a few seeds every ten days or so.
They do best in rich soils but are fairly shallow rooted so if your soil is lacking in nutrients it may be an idea to add a little compost or well rotted manure.
You can plant in the winter months in cooler countries under a cloche, cold-frame or in a Green house. They will, however, grow a lot more slowly than in the summer months.
Lettuce generally grow quite quickly and therefore are good catch crop and can be sown in between slower growing vegetables such as parsnips.