It can be tempting to prune your blackberry and raspberry bushes on the spur of the moment. The canes grow vigorously and without proper attention can easily take over more than their fair share of garden space. Pruning is not quite as simple as keeping brambles under control. Blackberries and raspberries require careful management for optimal production.
Know Your Canes
Before you prune, you need to know your canes. Both raspberries and blackberries produce two types of canes: primocanes and floricanes. These canes are biennial, meaning they have a two-year life cycle, whereas the roots and crown of the plant are perennial. Primocanes are berry canes in their first year, whereas floricanes are two-year-old canes. The floricanes provide the majority of the berry crop in both summer bearing and everbearing varieties. The primocanes of summer bearing varieties do not produce fruit. Everbearing varieties, on the other hand, produce a small fall crop from the buds towards the tip of the primocanes. The buds closer to the ground remain dormant until they become floricanes in turn.
Primocanes develop a thin, brown bark as winter approaches, preparing them for their second year. Your primocanes are now floricanes. The buds formed while the cane was a primocane grow into fruiting branches and bear fruit. How much fruit your plants yield depends on the variety and your location. Some plants produce a summer and a fall crop. Others give just one berry crop. Once the berries have all ripened, the floricanes die back as winter approaches.
The Pruning Process
Your job as a gardener is to prune your berry bushes to allow for optimal growth and to eliminate the dead canes that act as vectors for disease and pests. Berry bushes planted in rows are much easier to maintain than unruly patches. Rows allow you to control how many canes each plant puts out. This ensures each plant is spaced for optimal nutrient and light absorption. The majority of this pruning process consists of removing the spent floricanes.
It is easy to tell the old floricanes from the new floricanes. Spent floricanes have a peeling gray bark and brittle lateral branches. New floricanes lack these lateral, fruiting branches and the bark is brown. They put their branches out in the spring after you have already pruned. To prune the old floricanes, trim all dead floricanes as close to the ground as you can. Remove the dead canes to prevent any diseases from lingering and spreading to your plants.
Once the old floricanes are gone, you can focus on your rows. Keep your rows between 1 ½ to 2 feet in width. Limit the number of canes per foot to three to five. Trim back any new canes that attempt to expand beyond the row boundary. It pays to be a ruthless pruner. Eliminate any weak or sickly canes from within the row. Allow only the healthiest looking canes to grow. Sickly, weak plants attract pests and disease and do not produce the same quality or quantity of fruit.
Trellising your canes makes harvesting and future pruning easy. There are several different styles of trellis appropriate for blackberry and raspberry canes. Choose a trellis style that offers your canes support and allows for light penetration. Remember that while your row is only 1 ½ to 2 feet wide at the base, the canes branch out at the top. This branching is necessary for proper air circulation and light penetration. Air circulation is very important for disease prevention. Light penetration encourages new canes to grow within your row, instead of towards the outside.
The pruning process is broken into four easy steps:
- Removing old floricanes
- Maintaining your row width
- Thinning weak canes
- Trellising your canes
Following these steps gives you healthier plants with higher berry yields.
Best Time of Year to Prune
Resist the urge to pick up your nippers and trim back the briars today. Timing your pruning is very important for plant productivity. The best time to prune your blackberries and raspberries is late winter. Put on your jacket and a pair of thick gloves to protect your hands. Trim back last year's floricanes and remove them from the garden.
The benefit of winter pruning is that evidence put together by Cornell University suggests that the spent floricanes continue to send carbohydrates to the crown and roots throughout the winter. This helps the plant survive during its dormant stage. Unfortunately, late winter pruning is not practical for every climate, especially if your garden is usually snowbound until April. Snow and ice make it difficult to prune your canes down to the ground. Don't stress about getting to your berries in February if you live in an area with heavy snowfall. Prune your floricanes as soon as the snow melts enough for you to get to your berry beds.
You can also cut back your spent floricanes in the late fall. While carbohydrates are lost in this process, removing floricanes from the garden in the fall eliminates any risk of disease overwintering on the plant.
Thin your beds in early spring. Select the healthiest primocanes and floricanes and trim back the rest. Get rid of any canes damaged during the winter. Make sure you do not eliminate all the primocanes in favor of fruiting floricanes, as this will reduce your yield the following year. Early spring is a good time to top off your canes to a manageable height.
Blackberries vs. Raspberries
Blackberries and black raspberries differ from red raspberries in one important respect. The tip of the cane can form roots. This means that when the cane arches towards the ground, it can essentially replant itself. The good news is that you can easily propagate black raspberries. The bad news is that this growth habit quickly leads to overcrowding. Black raspberry and blackberry primocanes also put out side shoots, unlike the primocanes of red raspberries. Tip your black raspberries and blackberries by cutting off the last three inches or so of the primocane stem, once the canes are about thirty inches long. Not only does this prevent rooting, it also stimulates plant growth, providing you with more berries.