How to Prune Brambles
Of the many types of backyard brambles (Rubus), blackberries and raspberries are some of the tastiest and easiest fruits you can grow-but only if you prune the plants diligently and regularly. Pruning a bramble patch is not difficult, and nothing like the intricate combination of art and science needed to prune apple trees. Depending on the kind of bramble, it's just a simple three- or four-step procedure.
Why Prune Brambles?
Pruning brings air and sunlight to the stems (called canes) so they dry rapidly following dew or rain; quick drying prevents diseases. Left alone, brambles spread vigorously, and pruning also keeps them from taking over the rest of your garden. Pruning even makes harvesting the fruit less painful: rather than having to fight your way through a tangle of thorny canes, you can pick fruits splayed out for your convenience.
How Brambles Produce Fruit
Knowing how brambles grow and produce fruit can help you understand how to prune them. Although all kinds have perennial root systems, the canes are biennial: they die after their second year.
Brambles are grouped according to when they bear fruit:
Summerbearing brambles. Canes fruit only in the summer of their second year.
Everbearing brambles. A cane begins fruiting near its tip toward the end of its first season, then in the summer of its second season the cane finishes fruiting lower down. Because new canes grow from ground level each year, both kinds always have both 1- and 2-year-old canes, so the patch fruits every year.
When and How to Prune Brambles
Prune out old canes. The descriptions above offer clues to one step in the pruning process. When canes have finished bearing their summer crop, or sometime before your bramble patch wakes up again the following spring, cut to the ground any canes that have completed their second growing season.
How do you recognize those canes? Their old, cracking bark and the remains of fruit stalks make it easy to identify them. They look dead because they are, or nearly so.
Selectively prune excess new canes. Brambles send up so many new canes each year that they can become overcrowded, so you must also cut some of the new canes to the ground. Do this while the plants are dormant, ideally just as the leaf buds swell in spring, allowing you to see which, if any, canes suffered winter damage. First, go after new canes that have spread too far. Lop them to the ground to keep the row no wider than about 1 foot across.
Prune out unhealthy and crowding canes. Once you've narrowed the row, further reduce the number of canes. If your plants form a continuous row, prune so that the plants are at least 6 inches apart. If plants are spaced along the row-3 to 5 feet apart, for example-reduce each clump to 6 to 10 canes. As you lop, always spare the thickest and healthiest canes. Look for and remove all canes with gray disease splotches or swellings caused by borers. To prevent borers from spreading from pruned to healthy canes, dispose of prunings well away from the bramble patch, or burn them.
Prune to promote growth and make harvesting easier. I divide summerbearing brambles into three groups to describe the next pruning step.
Upright blackberries, black raspberries, and purple raspberries. These brambles bear fruit on branches growing from canes. Stimulate branch growth by pinching out the tip of any new cane when it's about 3 feet tall. Not all canes reach that height at once, so prune the patch a few times during the summer.
Sometime during the dormant season, prune the pinched canes again, shortening all the branches back to 4 to 18 inches. This allows sturdier branches to bear more fruit.
Trailing blackberries. Cut away old canes and reduce the number of new ones. During dormancy, shorten too-long canes to about 7 feet, then shorten the side shoots to 1 to 1 1/2 feet.
Trailing blackberries are usually trained to a trellis. After pruning, allow each season's new canes to trail on the ground, where they won't crowd fruiting canes.
Alternatively, train new canes on one wire or in one direction along the trellis, and train fruiting canes along the other wire or in the other direction.
Red and yellow raspberries. Fruit stalks grow on the canes, not on branches. Therefore, once the old canes and excess young canes have been cut to the ground, shorten the canes that remain (while plants are dormant). Longer canes produce more fruit.
Canes should be shortened for two reasons: to make harvesting easier and to prevent the canes from flopping around in the wind. How much to shorten them depends on your trellising method. You can surround the rows with two rows of wire strung between posts at each end of the row at 2 and 5 feet above the ground. Either tie the canes to the wires and shorten them to about 6 feet, or leave the canes nearly full length, then bend them along and around the upper wire.
Pruning Everbearing Brambles
Prune everbearing types of red and yellow raspberries as you would prune the summerbearing kind, with one difference. The year-old canes will have started fruiting at their ends late the previous year and will finish fruiting lower down the second year. Therefore, shorten those canes to just below where they stopped fruiting the previous year. Old fruit stalks hanging on the canes show you where to cut.
A simpler way to prune these raspberries is to cut the whole planting to the ground in autumn. By doing that, however, you lose the midsummer crop, harvesting only a late-summer or fall crop. The advantages are that pests cannot overwinter in the canes, and you don't need a trellis. Also, you needn't worry about damage from winter weather or browsing deer.
Three-Step Raspberry and Blackberry Pruning
Prune summerbearing red and yellow raspberries such as 'Canby', 'Latham', 'Titan', and 'Tulameen' like this:
1. After harvest and before new growth begins, identify and remove 2-year-old canes that have fruited.
2. Thin out 1-year-old canes growing beyond a 1-foot-wide row, and thin remaining canes to about 6 inches apart. Selectively remove those that are small, diseased, or broken.
3. The last step is to shorten remaining canes. If too long, they'll flop in the wind; too short, and you get less fruit. Tailor their length to your training system, leaving canes from 4 to 7 feet long.
Prune everbearing red and yellow raspberries such as 'Fall Gold' and 'Heritage' the same as summerbearing types until this third step. Everbearing raspberries fruit again in summer farther down their canes. Instead of shortening the canes to a convenient trellis height, shorten them to just below where they stopped fruiting the previous fall.
Prune summerbearing black and purple raspberries such as 'Bristol', 'Jewel', and 'Royalty', and upright blackberries such as 'Illini Hardy' and 'Navaho' like this:
1. In summer, pinch out the top 2 inches of growing canes that are approximately 18 to 36 inches tall. This stimulates growth of side branches that produce fruit the next season. Height is a matter of neatness and manageability. Pinch lower if you have no trellis, higher for trellis-trained plants.
2. Anytime after harvest and before spring growth, remove the canes that have produced berries, and remove excess 1-year-old canes.
3. Just before growth resumes in spring, remove damaged, diseased, or spindly canes. Shorten side branches (forced by summer's pinching) to between 4 and 18 inches. Leave the thickest ones longest.
The Fruiting Habit of Red or Yellow Everbearing Raspberries
1. In the canes' first summer and first fall, fruits grow at the tops of new shoots.
2. Early in the second season, fruits are borne low on last year's canes. But new canes are growing that will bear fruit in the fall.
3. Late in the second season, last year's canes are dead, and fruits come at the tops of new canes.
Lee Reich is a garden consultant and writer