Lettuce (Lactuca sativa L.) is the most commonly used salad vegetable, occurring in or under most salads. There are many types, varying in size, form, leaf shape, color and taste. All of these types may have evolved from a weedy form that was used in ancient Egypt as a source of cooking oil from pressed seeds.
Lettuce is grown worldwide, through the year. In warm climates lettuce farming is usually restricted to the spring and fall, when temperatures are more moderate than in summer or winter. Now it's time for winter sowing of lettuce. Like their summer counterparts, winter lettuces are available in a range of leaf types and can be sown now to get the autumn season off to a rewarding start. Sowing every few weeks through to November should ensure a leafy supply through to spring when less hardy varieties can be grown.
In the table below are listed countries with the biggest production of lettuce in EU and USA.
Winter lettuces are no different to summer ones in their requirements and in many ways starting them off later on in the season is easier as the heat and dry of the summer has passed. Lettuces are cool-season crops and hot weather can seriously hamper both germination and growth rates. Plants will not grow at all in very cold or frosty weather and a sunny position means frosted ground quickly thaws and growth soon resumes. Ideal if you have a polytunne or outdoors under a cloche or mini-tunnel.
From baby leaf lettuce to big, crisp heads, growing lettuce is easy in spring and fall, when the soil is cool. Leaf color and texture vary with variety. All types of lettuce managed best when the soil is kept constantly moist, and outside temperatures range between 45 and 75 degrees Fahrenheit. Lettuce doesn't like additional fertilizing. In fact, fertilizing too much causes the plants to produce very lush leaves that attract aphids. By avoiding fertilization, you can avoid most lettuce problems, including tip burn, bitterness and fungal disease.
Lettuce relates to human biology in several ways. The most obvious way is in its role as a food. As a green vegetable, lettuce contains many of the same nutrients found in other green vegetables, although mostly in lesser amounts. These include vitamins, minerals, water, fibers and others. Lettuce is a low to moderate source of vitamins and minerals. Among the various types of lettuce, Romaine and leaf varieties exceed crisphead and butter-head varieties for most of the common nutrients. In this table you can see nutritional values of lettuce.
Turning to nonfood uses, the stems and leaves of lettuce and its wild relatives contain a milky liquid called latex. The latex contains two substances called sesquiterpene lactones, which are the active ingredients in preparations used in some western European countries as a sedative and as a sleep inducer. In folk medicine additional uses for lettuce extracts include treatment for coughs, nervousness, tension, pain, rheumatism, and even insanity. The efficacy of these treatments is not well documented.
Another minor nonfood use is drying lettuce leaves for the production of cigarettes without tobacco. Actually leaves of a wild relative of lettuce produce a more tobacco-like appearance. These have been manufactured for use in several brands of cigarettes. Effects on health are not known.
The interesting fact is that in ancient Egypt lettuce had sexual symbolism. After completing its vegetative development with the formation of a head or a rosette of leaves, the plant goes into its reproductive phase with the formation of an erect seed stalk bearing flowers. The amount of latex in the plant increases and is under pressure, so if the top of the flowering stalk is cut off, the latex spurts out in a manner reminiscent of ejaculation. Consumption of lettuce may therefore have been thought to increase sexual prowess.
All about lettuce farming, including soil requirements and preparation, fertilizing, maintenance and other growing conditiones, you can find in Agrivi farm management software.