For any fruit or nut tree to pollinate, the male flower has to produce pollen when the female flower is ready to receive it. Pecan trees produce flowers of both sexes, but the trees are dichogamous, meaning that the release of pollen by male flowers does not coincide with the ability of female flowers to receive it. Different cultivars of pecan trees with male and female flowers that perform their functions simultaneously are ordinarily necessary to ensure that pollination takes place.
Male and Female Flowers
The pecan tree produces pendulous green spikes of male flowers, called catkins, that produce pollen. Pecan catkins grow in groups of two or three laterally along wood that is a year old.
The smaller, green spikes of female flowers that receive pollen grow at the end of the current year's growth. Both male and female flowers are about 1/8 inch long. The flowers of both sexes lack sepals and petals.
Some pecan cultivars produce male flowers first; other cultivars produce female flowers first. Both kinds of trees are necessary for pollination to occur, although sometimes the male and female flowers send and receive pollen at the same time. An orchard should have a mix of male-flower-first, female-flower-first cultivars to ensure pollination.
If a pecan tree is protandrous, the male flower sheds pollen before the female flower is receptive. Cultivars of pecan trees that are protandrous include Barton, Brake, Caddo, Cape Fear, Clark, Desirable, GraCross, Moore, Oconee, Onliwon, Pawnee, Peruque, Riverside, San Saba improved, Starking, Success and Western.
If a pecan tree is protogynous, the female flower is receptive before the male flower sheds pollen. Cultivars of pecan trees that are protogynous include Brooks, Burkett, Candy, Choctaw, Elliot, GraPark, GraTex, Grazona, Hays, Ideal, Mahan, Kiowa, Moreland, Shawnee, Sumner, Tejas and Wichita.
Effect of Climate
Climate can affect when blossoms on a protandrous tree produces pollen or when the blossoms on a protogynous tree are ready to receive pollen. Horticulturalists at the University of Georgia report that the Barton cultivar sheds pollen three days before the female flowers are receptive in Las Cruces, New Mexico. In Brownsville, Texas, male Barton flowers shed pollen 10 days before the female flowers are ready. Barton is protogynous in Georgia; its female flowers are ready five days before the males shed pollen.