If the thought of fighting thorny canes is the one thing between you and a summerlong source of homegrown blackberries, you’re in luck. Thornless blackberries first appeared with the 1911 introduction of Californian Walter Cory’s “Cory Thornless.” Now, multiple thornless cultivars supply months of gleaming, ebony fruit for preserves, baked goodies and eating straight away from the cane. Blackberries flourish in deep, mildly acidic, well-drained sandy loam. Cultivars demanding 200 to 800 hours of temperatures between 32 and 45 degrees Fahrenheit function nicely in Mediterranean climates.
Growth Habits
Thornless blackberries develop as erect, semi-erect or trailing plants. Of the three, only semi-erect plants require a trellis or other support. Erect thornless blackberries create canes in their roots and crowns; trailing and semi-erect cultivar canes sprout from the plants’ crowns. Called primocanes within their initial year and floricanes when they flower in their moment, the canes die back after creating berries.
High-Sugar Cultivars
“Navaho” (R. “Navaho”) brings high praise for its exceptionally sweet, late-June-to-August berries. A solitary, 4- to 5-foot “Navaho” plant bears from 8 to 10 quarts of 1-inch blue-black berries. The fruit 11.7 percent glucose content is the greatest among all University of Arkansas blackberry cultivars. Erect, heat-tolerant “Navaho” grows in full sun in U.S. Department of Agriculture plant hardiness zones 6 through 10. Apache” (R. “Apache”) produces hefty, gleaming-black berries on 5, 5- to 8-foot canes. Averaging 10.7 percent sugar solids, the fruit ripens over five weeks starting at mid-June, after its whitened, early-summer flowers open against medium-green, compound foliage. Up to 8-feet broad, “Apache” requires a sunny spot with room to spread. It’s hardy to USDA zones 5 through 9.
Medium-Sweet Cultivars
“Arapaho” (Rubus “Arapaho”), an erect thornless blackberry, produces white spring flowers and deep-green foliage. Its 8 to 10 quarts of 1- to 2-inch berries, desired because of their extremely tiny seeds, are ready for harvesting in ancient to mid-June. Spreading from 3 to 5 feet using canes of variable heights, self-pollinating “Arapaho” does well in partial to full sun. Its strawberries average 9.6 percent glucose content, marginally higher than the bigger, 9.5-percent fruit in “Natchez” (R. “Natchez”), another ancient blackberry. Introduced in 2007, semi-erect “Natchez” stands 4- to 5-feet benefits and high from trellis support. The white-flowering tree enjoys full sun, but does best in cool-summer climates in USDA zones 6 through 8.
Pruning Erect Thornless Blackberries
Properly pruning erect thornless cultivars like “Arapaho,” “Apache” and “Navaho” encourages them to ship lateral branches. Trim each year’s primocanes back to 3 1/2 feet in late summer or early fall. The cut canes become thicker as laterals emerge from their lower divisions, so that they support the growing harvest without aid. Cutting the laterals back to 1 foot in late winter or before they begin flowering in early spring promotes bigger blackberries.