Bolting

• A plant that produces seed stalks has “bolted.” Once lettuce has bolted, the leaves of most varieties taste bitter. Heat causes cool-season lettuce varieties to bolt early, so it is important to choose cultivars with a high tolerance for warm weather.
  
  

Crisphead Lettuce

• Cultivars of crisphead lettuce, also known as iceberg and cabbagehead, that are slow to bolt include Ithaca and Great Lakes. Saladin, a light green lettuce, is both rot and bolt resistant. Webbs Wonderful, a dark green variety, is another good choice for warm-weather gardening. You can harvest the outer leaves of Summercrisp, a hybrid between crisphead and loose-leaf lettuce, early in its growth -- until the head forms.
  
  

Romaine Lettuce

• Colonists started growing Cimarron during the 1700s. The plant produces crisp, red leaves and is slow to bolt. Bronze Mignonette and Romulus, both green lettuce varieties, grow well during the summer months. Horticulturists developed Vista specifically for desert areas with hot weather and low humidity.
  
  

Butterhead Lettuce

• Butterhead lettuce, also called bibb, grows smaller heads than crisphead varieties. Sunshine turns the green leaves of Perella Red, an heirloom variety, to a reddish color. The parts of the leaves not exposed to sunlight remain green. Dolly, with light or medium green leaves, is bolt resistant during warm weather. Sangria has a yellow heart with rose-colored leaves. Ermosa and bibb are good choices for humid regions of the country, such as Florida.
  
  

Loose-Leaf Lettuce

• Loose-leaf varieties are an easy lettuce for the beginning vegetable gardener. You can harvest the leaves throughout the growing season, as this variety never forms a head. A good green leaf variety for a small shady garden is Oakleaf, which requires only four hours of sunshine daily. Red Sails is the slowest red leaf lettuce to bolt, but Red Fire, with its ruffled leaves, is replacing it.