Vern Grubinger, University of Vermont Extension
Blueberries are a popular backyard fruit. Once established, they will provide lots of delicious, healthy berries for many decades with proper care.
To succeed with blueberries, plant winter-hardy varieties and maintain soil pH between 4.5 and 5.5. Mulch every few years with several inches of wood chips or sawdust. Apply a non-nitrate source of nitrogen fertilizer in early spring, irrigate as needed and use netting to exclude birds.
What’s also important, and frequently overlooked, is annual pruning. Late winter to early spring is a good time to prune.
Pruning is essential to maintain the vigor and yield of blueberry bushes. It promotes larger fruit, shapes the bush so it is easier to harvest and helps avoid insect and disease problems.
Pruning may be overlooked because the benefits are in the future. You don’t see them quickly. Another reason is that bushes with lots of leaves and quite a few berries may seem just fine, but without a well-pruned blueberry bush for comparison, it’s hard to see the benefits of pruning.
Early in life, blueberries don’t need much pruning. In years one and two, remove all flower buds by rubbing them off or cutting off the shoot tips. This directs the plant’s energy into cane growth.
Starting in year three, remove all twiggy or low-growing canes, and leave only two or three of the strongest, well-spaced new canes produced the previous year. In subsequent years, continue to remove all but two or three of the newest canes produced, leaving only upright, strong canes with space between them.
Different varieties produce different numbers of canes each year, so they vary in how much pruning they require. When a blueberry bush has reached full size in about eight years, it ideally will have 15 to 20 canes of all different ages.
Old bushes should not have a lot of old canes. These reduce yield because thick, older canes need more leaves to support fruit growth than they did when they were young. They also make it difficult for new canes to emerge and thrive, which is needed for sustained production.
If you don’t know the age of the canes, a rule of thumb is to remove canes before they reach one inch in diameter. These are usually gray with lichen growing on them.
If you’ve fallen behind in pruning, it’s time to remove several “dinosaur” canes per plant to create space for younger canes. Up to one fifth of all canes can be removed per year without yield loss. Berry numbers will be reduced, but fruit will be larger on younger canes and more space and light will benefit new canes that emerge.
Regardless of their age, it’s always good to remove dead, damaged or diseased canes, along with any that stick out too far sideways or grow very low to the ground. If two canes are growing very close together, one should be removed, so they don’t compete.
Try to open up the plant canopy. If it’s dense in the middle then air and light can’t get in, leading to high humidity. That promotes diseases and also provides comfort for the insect pest called spotted wing drosophila.
Use by-pass pruners to cut canes off as close to the ground as possible. High pruning cuts do not stimulate new canes to emerge from the crown. Instead, weaker side shoots will grow. Try not to leave any stubs.
Pruning every year, or every other year, really pays off in the long run. Your blueberry bushes will thank you — with plentiful berries.
(Vern Grubinger is a vegetable and berry specialist with the University of Vermont Extension.)