Several dozen superior black walnut cultivars have been identified and propagated over the last 100 years. Cultivars have generally been selected for their high-quality, thin-shelled nuts and high productivity. Other characteristics such as disease resistance, precocity, and annual bearing may have also influenced cultivar selection. The Southwest Center maintains a collection of 50 of these named black walnut cultivars (listed elsewhere in this report).

As black walnut is being domesticated and developed into a viable agricultural crop for Missouri, we need detailed phenological (life-cycle) information on these diverse cultivars to help us better plan our orchards for optimum pollination and freeze damage avoidance, but also to greatly advance the University of Missouri’s black walnut breeding program.

Black walnuts are wind pollinated and have separate male and female flowers in different locations on the same tree. Usually, the male and female flowers on one tree do not ripen at the same time, which promotes cross-pollination and avoids in-breeding among trees. Little is known about the male and female flowering cycles, spring bud-break timing, or nut ripening patterns among the various cultivars. Thus an attempt at documenting these characteristics on the most promising cultivars began in 2003 at the Southwest Center. Similar phenological data are also being collected at the University of Missouri’s Horticulture and Agroforestry Research Center at New Franklin, and at Kansas State University’s Pecan Experiment Field at Chetopa. A number of mature nut-bearing trees in our main walnut block are selected each year for observation and visited several days per week to document flower development. For spring bud break data, we are using young grafted trees planted in 2001. Some early, interesting results from these observations are presented below.

Black Walnut Cultivars at Southwest Center Sorted by Mean Bud-break Date

Black Walnut Cultivars at Southwest Center, Mt. Vernon, MO Sorted by Order of Mean Peak MALE Bloom Date

Black Walnut Cultivars at Southwest Center, Mt. Vernon, MO Sorted by Order of Mean Peak FEMALE Bloom Date