Pruning Red Raspberries

Photo/Illustration: Darlene White

Left unpruned, red raspberries are their own worst weed. When canes get overcrowded, they compete for sunlight, causing the shaded leaves and buds on the lower half of the plant to die. Without those buds, you’ll have fewer fruiting branches and a much smaller crop. Crowded canes also compete for nutrients and water, which leads to small, poor-tasting fruit. And the shady, moist conditions around a dense thicket are a magnet for fungal diseases, such as gray mold, spur blight, and anthracnose.

 Pruning is the most effective way to avoid these headaches. A yearly thinning allows plenty of sunlight and air to penetrate the bramble, which means you’ll have bigger, healthier crops and a much easier time picking those sweet red berries.

Before you start, know your primocanes from your floricanes

Red raspberry plants, after pruning. Photo/Illustration: Ann Stratton

To prune any plant properly, you need to understand its growth cycle. In the case of red raspberry, the roots and crown are perennial but the canes are biennial (they live for only two years). The first year, they emerge as green primocanes and form fruiting buds. If you have a summer-bearing variety, these buds won’t flower until the following year. If you have an everbearing variety, the buds at the tips of your primocanes will give you a small fall crop, and the buds lower on the canes will remain dormant until next season. As winter nears, primocanes drop their leaves and develop a thin brown bark.

 In their second year, the canes are called floricanes. The previous year’s buds grow into fruiting branches and bear a summer crop. As their berries ripen, floricanes begin to senesce. Their leaves turn red or yellow, and they die as winter approaches. A big part of pruning a red raspberry is getting rid of these spent floricanes. To keep your plants from getting unruly during the growing season, cut back any new canes that emerge outside the desired row width of 2 feet; however, don’t touch the new green shoots growing within the prescribed row width. It’s not until late winter that you prune the entire plant.

 In fall, resist the temptation to cut out the dying flori­canes that fruited that summer. Research conducted at Cornell University indicates that these canes send carbohydrates to the crown and roots well into early winter, helping the plant survive dormancy.

What about black raspberries?

The canes of black raspberry are biennial, just like those of red raspberry. But because black raspberry’s growth habit is different, this plant requires an extra pruning step.

 The canes of black raspberry tend to grow longer than those of red raspberry. The tips of the canes arch down to the ground and form their own roots, essentially creating new plants. While this makes black raspberry easy to propagate, it also leads to overcrowding. The other major difference is that the primocanes of black raspberry develop side shoots or branches, which only develop on the floricanes of the red variety. These shoots form buds that will bear fruit the following year. To encourage more fruit-bud development and prevent the cane tips from rooting, you should tip the primocanes of black raspberry in summer before they get too tall. When the canes reach about 30 inches long, simply cut off the top 2 to 3 inches of stem growth. This will encourage more side shoots and fruit buds as well as keep the canes at a more workable height. In late winter, prune the canes as you would for red raspberry. Note: Although you can train black raspberry on a V trellis, a single wire trellis will better accommodate the plant’s branching habit