When in bloom, blackberries (Rubus fruticosus) attract bees and butterflies to the sweet nectar within the flowers. Blackberry bushes can be grown in gardens in U.S. Department of Agriculture plant hardiness zones 5 through 10, and they can often be seen growing wild along rural roads and in the woods.
Timing for blackberry blooms varies depending on the weather of the region where they're planted and the variety. In warm climates -- USDA zone 7 and south -- blackberries start blooming from mid-April to early May. In cooler climates north of zone 7, blackberries begin to bloom in late May.
For earlier harvests, look for early-blooming varieties such as Choctaw (Rubus fruticosus 'Choctaw'), which grows in USDA zones 8 to 9 and is vigorous but thorny.
Blackberries start ripening about 60 to 70 days after the blooms first open, depending on the variety. Some varieties, like the Arapaho thornless blackberry (Rubus fruticosus 'Arapaho,' USDA zones 5 to 10) produce ripe fruit about 11 days before the Navaho (Rubus fruticosus 'Navaho,' USDA zones 6 to 10), which is the world's first erect-growing thornless blackberry.
While blackberries are self-fertile -- they do not require a nearby male plant for pollination -- it's beneficial to grow several blackberry plants in the same area. Having several plants together provides more pollen for bees to collect and more blooms to pollinate. More blooms close together means better pollination for each plant. If you have only a small space to grow blackberries, a single plant will produce blooms by itself.
Different types of blackberries can cross-pollinate each other, as long as they are in bloom at the same time. Several different varieties can be grown in the same area and still get the benefit of cross pollination.