Lettuce is the name given to a group of green leafy vegetables most commonly used in salads. There are many varieties of lettuce including iceberg lettuce, which is the most popular and common type of lettuce in the United States. Lettuce was first cultivated in Egypt and slowly spread around the world. Today, it is grown in many countries of the world and the largest producers of this vegetable are China (12.5 million tonnes), the United States (4 million tonnes), India (1 million tonnes), Italy and Spain (both about 800,000 tonnes). Let’s take a look at how those green leaves in your salad grow.
How are lettuces grown?
Lettuces are grown commercially in large farms and they are commonly grown in greenhouses where conditions can be kept constant. The seeds are either planted directly into the soil or in a special mixture designed to promote growth and they are then later replanted when they become seedlings. The lettuces are placed about 20 – 36 cm (8 to 14 in) apart to ensure they all receive adequate sunlight. Most varieties of lettuce require nitrogen rich soil, full sunlight, and temperatures under 24 °C (75 °F). Once the lettuce is ready it is harvested and immediately stored at low temperatures and high humidity. It should never be stored near ripening fruit because it will degrade quickly.
Did you know?
The soil for growing lettuce not only needs to contain nitrogen, but other nutrients such as boron, calcium, phosphorus, copper and molybdenum are also important to the proper development of a lettuce.
Lettuce is very attractive to a number of insects and other pests. It has been discovered that many varieties have developed natural pest repellent compounds. Genetic engineering and selective breeding is being used to develop more pest resistant varieties of lettuce.