Blackberry plants have perennial roots and biennial canes. The shoots (canes) of blackberries are strictly vegetative during the first growing season. These first year canes are referred to as primocanes. The following year, these same canes (now called floricanes) flower, produce fruit, and then die.
In Iowa, most blackberry varieties suffer extensive winter injury. As a result of this damage, plants produce little or no fruit. However, new primocane bearing blackberry cultivars may make it easier to successfully grow blackberries in Iowa and other northern states. The canes of primocane bearing blackberries don't need to survive the winter as they produce a crop in late summer/early fall on the current year's growth.
The new primocane bearing blackberries were introduced by the University of Arkansas in 2004. Prime-Jim™ and Prime-Jan™ are named after Dr. James Moore, founder of the University of Arkansas fruit breeding program, and his wife, Janita. Prime-Jim™ and Prime-Jan™ are erect, thorny plants. Plants exhibit good vigor and health. Fruit are medium-sized, conical, soft, good flavored with a glossy black color. Temperatures above 85°F in late summer and early fall can reduce fruit set, berry size, and fruit quality.
In Iowa, gardeners should prune the canes of Prime-Jim™ and Prime-Jan™ back to the ground in late winter. Additional information on growing blackberries in Iowa can be found in the June 29, 2005 issue of the Horticulture and Home Pest News.