There are hundreds of lettuce cultivars varying in color, leaf shape, texture and growth habit. Lettuces generally come in a spectrum of green or red, with several varieties having both green and red leaves. Lettuce leaves can be oblong, flat, frilly, delicate, scalloped or ornate like oak leaves. Most Americans are familiar with iceberg lettuce and romaine lettuce but there are several common cultivar groups: Looseleaf lettuces are grown for their small, immature leaves and are used in salad mixes. Butterhead, or Bibb, lettuces are grown to maturity, with a loose round head of tender, easily bruised leaves. Summercrisp lettuces tend to bolt (go to seed) slower than other types, which makes them ideal for warmer climates. Farmers growing looseleaf lettuces for salad mixes choose varieties with different textures in order to give the mix volume and colors to make them visually appealing.
Lettuce grows best in cool temperatures. It can often overwinter, but doesn’t grow rapidly until temperatures warm and daylight increases. With the exception of some summercrisp varieties, most lettuces will bolt when temperatures consistently reach 75 degrees. Once the plant begins the process of bolting, the leaves become filled with a milky substance, which makes them taste bitter. When bolting, the plant will shoot up a stem, which eventually results in dozens of dainty flowers. Once the flowers are pollinated they become feathery and, like dandelion seeds, the seeds can be spread easily by wind.
Buying lettuce from local farmers means it’s fresh. Unlike packaged bags of mixed greens at the grocery store, a bag of fresh, local lettuce can last up to 2 weeks in the refrigerator. Arizona grows nearly 30% of all lettuce for consumption in the United States. Most of this is grown near Yuma during the winter. Lettuce is an excellent source of vitamins K and A and good source of folate and iron. Darker lettuce greens contain more nutrients, while iceberg lettuce contains very few.