With the advent of consistently warmer to hot weather in much of Southern California, many of the cool season leafy green vegetables, such as lettuce, will have flowered and gone to seed, or bolted. Those gardeners who live in Southern California areas with significant coastal influence may still be able to grow these leafy green vegetables throughout the summer.
Lettuce often bolts as temperatures rise. GardenZeus recommends using shadecloth or providing shade to lettuce when daytime temperatures rise above about 78° F. For specific information on shading, see GardenZeus Tips for Shading Vegetables During Hot Weather. At 85° F to 90° F temperatures and above, virtually all varieties of lettuce will suffer, become bitter, or bolt in from a few days to 2 to 3 weeks. There is nothing that can be done to reverse or stop bolting once it begins.
Leaves may begin to turn bitter as soon as lettuce starts to flower. GardenZeus recommends tasting leaves for quality and if still reasonable, harvesting the majority of leaves or whole plants at the first sign of bolting, unless you want to save seeds. As lettuce plants bolt or begin to grow bitter, soak plants or leaves in cool water overnight to draw out white sap that is produced in leaves and stems as plants prepare to set seeds and which causes bitter flavor.
Treat other greens such as arugula, parsley, mache and spinach in the same manner: harvest the majority of leaves or whole plants at the first sign of bolting, unless you want to save seeds.
Gardeners with bolting leafy greens can use this as anopportunity to engage in sustainable gardening practices.
Sustainable Landscaping Tip 1: when your parsley begins to bolt, leave the parsley in place. Flowering parsley provides food for many beneficial insects, so bolting might not be a problem in the larger plans of an insect-friendly gardener.
Sustainable Landscaping Tip 2: when your arugula begins to bolt, leave the arugula in place. Arugula will naturalize in many parts of California and you may be rewarded next year with effortless supply.
To view customized information for growing lettuce, arugula, spinach and mache, go to GardenZeus and then to the appropriate plant.