Blackberry Summer

New selections have lost the thorn and extended the growing season.

By Linda Askey

New thornless varieties make harvesting easier.

New thornless varieties make harvesting easier.

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Blackberries are the essence of the season. The wild patches we frequented as kids offered juicy, sweet summertime treats. The pleasure, however, came with a price—plenty of scratches where thorny canes met bare arms and legs. Now garden-grown blackberries are bigger, sweeter and, best of all, thornless.

Most of the big-fruited, thornless selections had their beginnings in the research plots of the University of Arkansas, currently directed by Dr. John Clark, who has been working on these blackberries for 35 years. “Our blackberry program has impacts all around the world,” observes Clark. Thanks to decades of work, a wayside berry has turned into a crop worthy of a garden, a farm or, more importantly, your table.

A Year in the Life

Unlike shrubs or trees, blackberries are perennials that renew from the ground. They have vegetative canes called primocanes that, for most selections, become fruiting floricanes. No cane lives longer than two seasons. When an established plant breaks dormancy in spring, floricanes put out leaves, bloom and begin developing fruit. Meanwhile, the new shoots called primocanes begin to emerge just at or below soil level. As soon as the berries ripen and are picked, it is recommended that the spent floricanes be removed by cutting them to the ground. The primocanes will continue to grow for the next season, becoming floricanes.

Not only is picking easier when plants are thornless, but so is pruning. Once you decide to grow the thornless ones, there are no bad choices. By growing several selections, you can extend your harvest to about five weeks. Below are a few selections Clark recommends.

Cold Hardiness

Varieties and chilling periods. Click to enlarge.

Varieties and chilling periods. Click to enlarge.

Blackberries are almost a sure bet in USDA zones 7, 8 and 9, with good possibilities in Zone 6. Where plants are marginal, some growers are using a trellis that can be collapsed and then sheltered with a row cover.

When considering his thornless selections, Clark recommends, “Ouachita is best, based on last winter,” meaning that Ouachita tolerated the cold better than others. On the other hand, continues, Clark, “Chester Thornless is not an Arkansas development, but it is likely the hardiest of the thornless. It is a high-chill, semi-erect, USDA development. It is very productive, but tart.”

Always check the chilling requirements for the different selections and choose the best match for your climate. Also check with your local Extension Service to learn what has worked and what has not.


Clark recalls, “About 15-18 years ago, we discovered the first primocane fruiting plants in our breeding program.” The significance for both gardeners and growers is huge—the entire patch can be bush-hogged in the fall. Then, the next spring, the canes emerge, flower and fruit. Repeat.

The first primocane selections were released for gardeners in 2005 called Prime-Jim® and Prime-Jan®, but they are not recommended for farmers because they would not ship. However, the thornless ‘Prime-Ark® Freedom’ was released as an innovation for gardeners and growers alike.

Because primocanes fruit later in the season, these plants have the potential to greatly extend the crop for late summer and fall berries. Although more research and trials need to be performed before we know for sure, there’s also the possibility that these selections can be grown in zones where floricane varieties cannot.

“Not needing to overwinter the canes is promising,” says Clark. In other words, those varieties that can simply be mowed down do better in colder climates.

If the gardener can mulch [the plants] substantially, says Clark, “that would be like snow cover to help get the plants through the winter.” However, notes Clark, “there’s not a lot known yet. When you get to the upper Midwest, the floricane fruiters are not going to survive. They are not hardy enough.”


Want to learn more? Check out the following:

Blackberry Production in the Home Garden:

New Arkansas Blackberry Production Characteristics:

Prime-Ark® Freedom Thornless Primocane-Fruiting Blackberry

Rotating Cross-Arm (RCA®) Trellis System: