Blackberries, black raspberries, and raspberries are different species of brambles, so their management can differ. Raspberries can have either red or yellow fruit, but they are the same species of plant and so they have the same management. Brambles also come in 2 groups: summer bearing (floricane) and everbearing (primocane). For the items described in this article, we assume you are growing summer-bearing (floricane) cultivars.
The bulk of the pruning of brambles is done in the winter, but some pruning is done in the summer. Generally, blackberries and black raspberries are pruned during the growing season in a practice called tipping. Tipping is the removal of the tip of a non-woody shoot (primocane) that emerged at the start of the growing season (Figure 1). The goal of tipping is to induce the primocanes to branch laterally. For blackberries and black raspberries, inducing lateral branches during the growing season increases the amount of fruiting buds that will grow from them the following season. In raspberries, this practice is not recommended, as they yield better when those fruiting buds originate from an unbranched cane.
The ideal tip height is generally around 2-4 feet, but this is subjective based on the height of your trellis. When tipping, remove around 3-6 inches of the tip of the shoot once the primocanes reach the desired height (Figure 2). In Iowa, blackberries are marginally hardy and some growers tip them when they are as short as 2 feet tall to increase the chances of the lateral canes being below the snow line for insulation during the winter.
What about purple raspberries? They are hybrids of raspberries and black raspberries. Some purple raspberry cultivars grow more like raspberries, and others grow more like black raspberries. Many of the more popular purple raspberry cultivars are grown like raspberries and are not tipped in the summer.
In summary
- Black-fruited brambles (blackberries and black raspberries) should be tipped in the summer to induce lateral branches.
- Red or yellow-fruited brambles (raspberries) should not be tipped in the summer.
- If your raspberry canes get taller than you want, you can prune them shorter when they are dormant in the winter. However, if you remove more than ¼ of the top, you severally reduce your yield
More information about pruning raspberries can be found in this publication: Pruning Raspberries
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