Number of Flower Heads
Most of the tall varieties of sunflowers, such as "American Giant" and "Kong" have one flower head per stem. Other types of sunflowers bloom with multiple flower heads on each stem. Most of these sunflower plants are bushier in appearance, are usually dwarf varieties, and are good for cultivating in containers, according to the University of Minnesota Extension.
Single or Double
Although sunflowers technically have hundreds of flowers on each bloom, most gardeners classify the plants by the type of flower head, which can be single or double. A single sunflower means that each bloom has a single layer of petals, or ray flowers, surrounding the center. A double sunflower has two rows of ray flowers.
Re-Blooming
Sunflowers grown as annuals die after producing their flower heads go to seed. They do not grow and bloom again. These are usually the varieties cultivated for their large size, showy flower heads and edible seeds. A few types of sunflowers, however, can be grown as perennials, which means they will grow more flowers again the next season. Although most do not like hot, humid conditions, many are hardy in climates as warm as U.S. Department of Agriculture plant hardiness zone 9. Two of the more commonly grown sunflower perennials are H. salicifolius, which has long, thin, graceful leaves, and H. maximiliani, which is large for a perennial sunflower -- it can reach heights of 10 feet. Both H. salicifolius and H. maximiliani are hardy in USDA zones 4 through 9.
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