Lettuce (Latuca sativa)
Another vegetable that has been cultivated for thousands of years, lettuce was grown by the Sumerians in the area that is modern-day Iraq. Lettuce is recorded in ancient Egypt, described in carvings at a temple in Karnak, and was thought to be an aphrodisiac. It was also grown in Asia for at least as long. The Latin name Latuca is derived from lac, meaning “milk,” a reference to the milky juice that appears when it is cut. Curiously, the milky juice that gave lettuce its name contains a substance called Lactucarium, which is similar in properties to opium, though much milder. All lettuce varieties contain this chemical, and all are soporific. It may be the salad that sends you to sleep after Christmas dinner, and not the turkey.
Agustus Caesar is said to have commissioned a great statue of Romaine lettuce because he felt that he had been cured of a grave illness by eating its leaves. The “Caesar salad,” however, was invented in Tijuana, Mexico, by Italian immigrant Caesar Cardini in 1924.
Eventually, under Roman influence, lettuce came to be grown in France, first appearing at the papal court of Avignon. Until the reign of Louis XVI, lettuce had primarily been eaten as a hot dish, not raw. A French nobleman known as Chevalier d’Albignac introduced lettuce salads to London in the mid-18th century. According to the culinary writer Brillat-Savarin, this French salad enthusiast made something of a small fortune for himself, visiting hotels and restaurants equipped with a set of dressings that included flavoured oils and vinegars, caviar, soy sauce, anchovies, and meat juices.
Lettuce is an annual (occasionally biennial) member of the sunflower family, Asteracea. The succulent leaves grow in a rosette form, and eventually send up a tall flower spike that, in turn, forms seeds not unlike those of the dandelion. This typically happens in periods of warm weather, and is referred to as “bolting.” Because of its tendency to bolt in summer, lettuce is grown as a cool season crop in early spring and again in the fall. By employing tricks like shade cloth in summer, “bolt-resistant” varieties, and cloche cover in cold weather, lettuce can be grown in mild climates 12 months of the year.
There are four main types of lettuce. Round lettuces are sometimes called butterheads or Bibb lettuce, and tend to have relatively open, soft, delicate leaves. Crisphead lettuces have an entirely more crisp texture, and include the tightly packed heads of iceberg lettuce, as well as the more open, flattish Batavian types. Romaine lettuce (popularly known as “cos” in the UK), grows in a more upright fashion, with wide leaves and firm, crisp petioles. Finally, there are the loose-leaf lettuces with their completely open growth and leaves sprawling out from the centre.
Lettuce, with its fast growth cycle and easy cultivation, is particularly well suited for breeding and crossing. Nearly all varieties are open pollinated (there are very few hybrids), and a great many varieties exist. The Roman writer Pliny described nine varieties in the 1st century AD, and Thomas Jefferson grew 19 different lettuces in his retirement at Monticello. All this breeding has resulted in hundreds of varieties, with a wide range of textures, colours, and flavours. Iceberg lettuce was bred to have nearly no bitterness, while others have a flavour similar to sharp arugula. Finding a handful of favourites is largely a matter of trial and error, and personal taste.
How to Grow Lettuce:
Difficulty: Easy. Lettuces are well suited to containers over 4” deep.
Timing: Lettuce grows best in cool weather in the spring and fall. Sow in April and plant every 2-3 weeks for a continual harvest. Using a cloche or cold frame over mid-late August plantings can extend harvests into winter.
Sowing: Either direct seed or start indoors and transplant. Plant seeds on the surface and gently tamp them down. Seeds sprout in 2-15 days depending on soil temperature. Seeds don’t sprout easily when the soil temperature is over 21°C (70°F) in July and August. Get around this by sprouting them indoors in a cool area, or pre-sprout by sprinkling seeds on a damp paper towel, placing it in a plastic bag in the fridge for a few days. One gram of seed sows at least 10m (35’) of row so don‘t plant the whole package at once! In hot weather, lettuce goes to seed quickly, so have new plantings ready to go. Direct seed 2.5 (1”) apart in short rows 30-45cm (12-18”) apart.
Soil: Soil with lots of organic matter than drains well works best. Add compost and lime 3 weeks before planting. 1 cup of complete organic fertilizer per 3m (10’) of row will give adequate nutrition. Aim for a pH level of 6.0-7.0.
Growing: Seedlings should be hardened off by reducing water and putting the plants outdoors 2-3 days before transplanting. Thin or transplant loose-leaf types to 20-25cm (8-10”) apart. Heading types should stand 30cm (18”) apart. Regular watering is essential to prevent leaves from getting bitter.
Harvest: Pick individual leaves from the outside of the plant or wait and harvest full heads. Summer lettuce stays in prime eating condition only a short time, so harvest promptly and keep planting. In fall and winter the plants stay in good condition longer.
Storage: The trick is to always have fresh on hand so storage is unnecessary. Lettuce will keep in the refrigerator for several days. Store it in the vegetable crisper inside a loose plastic bag.
Seed info: In optimum growing conditions at least 80% of seeds will germinate. Soil temperature for germination: 10-22°C (50-72°F). Usual seed life: 3 years.
Growing for seed: Stagger plantings so that different varieties flower at different times throughout the summer. Otherwise, isolate varieties by 10m (30’) if growing for seed.Pests & Disease: Crop rotation is good for disease prevention. Tipburn (tips of leaves turn brown) is caused by a calcium deficiency, but if you have limed and added fertilizer, tipburn is likely due to lack of moisture. Slugs are a problem in early and late plantings.