Alfalfa: Although alfalfa is almost always grown for forage in Ohio, a few growers occasionally harvest seed. Before pollination can take place, the sexual column containing the stamens (filament and pollen carrying anther) and pistil must be "tripped." The mechanism is tripped when a bee inserts its tongue into the corolla of the flower. When the sexual column is released, it strikes the underside of the bee's head and deposits pollen. Pollen from a previous flower is then transferred to this flower.
Honeybees "learn" that the sexual column will strike them and soon learn to enter the corolla from the side of the flower, failing to pollinate the flower. However, some bees intentionally trip the flowers to obtain pollen.
Strains of honeybees that have been selected and bred for increased alfalfa pollen collection are being tested for increased alfalfa pollination and improvement of alfalfa seed production.
In California and Arizona, 2 to 3 colonies of honeybees are rented per acre. Considering the difficulties of attracting honeybees to alfalfa in Ohio, an even greater rate may be needed. However, the precise pollination requirements are unknown for Ohio conditions, and in light of the competition, alfalfa seed production is probably impractical in Ohio.
Red Clover: Red clover is an important seed crop in Ohio. The flower tube varies in length and is sometimes too long for nectar gathering honeybees. Two or more colonies of honeybees are required per acre for maximum seed yields.
Other Legumes: Alsike, white, crimson and sweet clovers; trefoils; and vetches, all require bee pollination and are attractive enough to bees to produce a honey crop. One to 2 colonies per acre is advisable for seed production. Crown vetch, grown extensively for soil conservation uses, produces little or no nectar and is unattractive to bees.