There's been a recent surge of interest in growing small fruits in the landscape. That's a good thing because many small fruits, such as blueberries, strawberries, and raspberries, are not only delicious harvested fresh from the garden, they are also easy to grow. Plus, these fruits work well in the landscape -- you can create an edible fence with brambles, use blueberries as foundation plants, grow a strawberry ground cover, and adorn a trellis with grapes.
In general, growing these small fruits is straightforward; however, pruning them can be a head-scratching proposition. This is especially true for brambles, such as raspberries, blackberries, and black raspberries. When do you prune? How do you prune? Let's go through the basics.
It's easy to remember how to prune brambles if you understand how they grow. The underground parts (the roots and crown) are perennial, but the canes (stems) that arise from the crown are biennial, meaning they live for two years. In its first year, a cane grows vigorously, develops a strong structure, and stores energy. In its second year it produces fruit. After fruiting, the cane declines and dies. (With one exception: The canes of "everbearing" raspberries and blackberries produce fruit late in their first season and again in their second year. More on that later.) Since a 2-year-old cane dies after producing fruit, the rule of thumb is to cut back 2-year old stems to the ground immediately after the harvest, pruning carefully to avoid damaging the crown or young shoots. However, each type of bramble has a slightly different growth and fruiting habit, and therefore pruning method. Here are specifics on how to prune each type.
Summer-bearing red and yellow raspberries produce tall, unbranched canes as well as root suckers (canes that arise from the roots rather than the crowns). That's why these are good choices for an edible fence -- they spread quickly to form a raspberry hedge. However, the suckers don't discriminate where they grow and left on their own they'll spread everywhere, including perennial beds or lawns. You must be diligent about weeding them out of unwanted areas or they'll take over.
Red raspberries need a strong trellis to keep the canes off the ground. Cut back canes in spring to force side branches and more fruit that summer.
To create a productive and manageable planting, prune raspberries in late winter or early spring before new growth begins. If growing in rows, remove canes until there are eight strong canes per 3 feet of row. If growing in a bed, thin until there are six to ten canes per square foot of row. Another way to measure is to leave 4 to 6 inches between canes. (Thinning canes to this spacing produces larger fruits.) After harvesting the fruits in summer, cut these fruiting canes back to the ground, leaving the first-year canes alone. The following spring as growth is beginning, prune back the tips of these canes (now in their second year) so they stand erect and about 4 to 5 feet high.
Despite being called everbearing, these raspberries actually produce two crops a year: one in summer and another in fall. Unlike summer-bearing raspberries, first-year everbearing raspberry canes produce a crop of berries on the tips in the fall of their first year. The cane survives the winter and produces fruits lower on the same cane the following summer. One way to prune is to remove the tip of the cane after the fall harvest. Then after the following summer's harvest cut these 2-year-old canes back to the ground.
Another way to prune everbearing raspberries is to mow the entire bed to the ground after fall fruiting is finished. This will sacrifice the summer crop, but will result in a larger fall crop. It also reduces pest problems.
Unlike their red and yellow cousins, black and purple raspberry canes branch vigorously and grow in a vase shape, producing few if any root suckers. If allowed to grow unpruned, the long canes will bend and those that come into contact with soil will form roots, giving rise to new plants. It's a good way to propagate more plants from your existing ones, but left unchecked can result in an impenetrable and unruly planting.
First year canes should be allowed to grow straight and strong. The healthier the first year canes, the more fruit they will produce the second year.
Here's how to create a productive, manageable planting: In spring, when first-year canes reach 18 to 20 inches tall, prune back the tips by 6 inches. This encourages strong side branching. The following spring, trim each of these side branches back to 8 to 12 inches. Thin canes, leaving five to ten canes per plant, depending on the soil fertility. The more fertile the soil, the more canes you can leave.
Blackberries are pruned in a similar fashion to raspberries, including the new everbearing blackberry types, such as 'Prime-Jim' and 'Prime Jan'. Most varieties form fruits on two-year-old canes and those canes are removed after fruiting. However, other pruning techniques depend on the type of blackberry you're growing. Upright blackberries, such as 'Cherokee', produce stiff, erect canes that stand on their own and form berries at the cane tips. Although they can be trellised, they don't require it. When the new first year canes are about hip high, pinch back the growing tip of each one by 2 inches. This encourages the canes to branch out during the rest of the season. The more branches, the more fruit next year.
On thornless trailing varieties, such as 'Hull', the fruits form all along the supple canes that need to be supported on a wire trellis. Since they form fruit all along the cane, the first year old canes don't need to be pinched to produce more fruits. However, in warm areas the trailing canes may get so long they should be pruned back in late winter to 7 feet long to keep them within bounds. This will also help them form side branches or laterals that can be pruned back to 1 to 2 feet in late spring.
At any time of year you can remove dead, damaged, or diseased canes on any bramble.