 Generally grown as a hardy annual , lettuce is easily cultivated , although it requires relatively low temperatures to prevent it from flowering quickly . It can be plagued with numerous nutrient deficiencies , as well as insect and mammal pests and fungal and bacterial diseases . L. sativa crosses easily within the species and with some other species within the Lactuca genus ; although this trait can be a problem to home gardeners who attempt to save seeds , biologists have used it to broaden the gene pool of cultivated lettuce varieties . World production of lettuce and chicory for calendar year 2010 stood at 23 @,@ 620 @,@ 000 metric tons ( 23 @,@ 250 @,@ 000 long tons ; 26 @,@ 040 @,@ 000 short tons ) , over half of which came from China . 
