Pruning is required to maintain blueberry plant vigor and productivity, to aid in disease and insect management, to maintain large fruit size and quality, and to develop an appropriate growth habit for harvesting.
Proper pruning balances the production of strong, new wood while maintaining good fruit production. When plants are pruned too lightly, they become dense, with weak, twiggy growth, and fail to develop strong new wood for future fruit production. Severe pruning leads to the production of fewer, larger berries and more new wood. Experience is the best guide on how much to prune.
The best time to prune is from January to mid-March, during the dormant period. However, blueberries can be pruned any time from the end of harvest to bud break the following spring. There is some evidence that early pruning (mid-September) delays bloom the following spring. By pruning in late winter, one can identify and remove winter-injured wood. Also, carbohydrates produced in late autumn will have had sufficient time to move into the roots and crown for storage.
Annual pruning is essential for consistent production of high quality fruit. If bushes are pruned only occasionally, then many young canes will be produced the year after the heavy pruning. These canes will age together, and become unproductive at the same time. After several years, if one would want to prune out the unproductive canes, nearly the entire bush would have to be removed. In addition, no young growth would be present to replace the lost fruiting wood.
Irregular pruning results in erratic yields from year to year, and very large bushes with individual canes competing for light. Research has shown that annual, moderate pruning results in bushes with the fewest canes, but with the greatest yields.
Pruning equipment consists of high quality pruners and loppers. Gloved hands may be used to strip flower buds off young plants and to break twigs. Disinfect loppers and pruners between bushes by using a solution of one part bleach to nine parts water or shellac thinner. The bleach solution may cause pruners to rust quickly. Some growers use hydraulic or pneumatic pruners to increase speed.
Pruning 2-year-old plants at the time of planting is limited to removing the older twiggy growth from the base of the plants, leaving the strong new growth. Strip blossoms off young plants the first year or two in the field. Permitting young plants to set fruit slows growth. Long-run production will be best if, during the first 2 years after planting, plant top and root growth, rather than berry production, is emphasized.
In subsequent years, while plants are still immature, prune lightly. Remove injured, weak, or diseased wood, and any twisted or low-growing canes, to promote new growth. If more than two new canes were produced the previous year, remove all but the two healthiest at crown level. When plants are about 7 years old they should have from 10 to 20 canes of different ages.
Pruning established mature plants consists of cutting out, or cutting back, old canes that have weak new wood, and eliminating the weak, twiggy growth in the top or outer areas of the bushes. Weak, twiggy wood generally has few flower buds and produces small berries.
Following a series of steps may systematize your pruning job and make it easier. The first-year canes are not branched and will not produce much fruit during the coming season, but they are essential to crops in succeeding years. The second- and third-year canes have laterals with good vigor and many strong fruit buds. They are the best fruiting wood.
Fourth-year and older wood with small, weak laterals and few fruit buds is not productive. It crowds and weakens young wood and should be removed. Cut canes back to the ground or a strong new side shoot. If one or two old canes are removed each year, and one or two new ones produced, none will be over 4 to 6 years old a good goal to work for.
The following is a summary of the steps to take in pruning:
- Remove the low growth that would touch the ground when loaded with fruit. Cut out short, soft, new shoots that developed from the base of the plant late in the season.
- Remove canes and twigs damaged by winter injury, mechanical causes, diseases, or insects.
- Cut out weak, twiggy wood from the top and outer parts of the plant. Remove enough from the top to let light down into the plant center.
- If necessary, cut out some (usually one or two) older canes. Cut out the weakest canes. Sometimes it is better to cut the cane back to a strong new side branch, rather than pruning it back to the ground.
- If your plants tend to overbear, thin the fruit buds by tipping back some of the small shoots carrying a heavy load of flower buds. Blueberry flower buds are near the tips of the past season’s growth (see The Highbush Blueberry Plant).
Pruning severity may need to be adjusted to balance the production of a good, quality crop with adequate growth for subsequent years’ crops. Experience is the best guide for proper pruning.
Weak bushes require more pruning than vigorous bushes because pruning stimulates vegetative growth. Special consideration must be given to cultivars with spreading habits. Sprawling canes should be removed, but care should be taken to leave sufficient canes for fruiting.
When rejuvenating an old planting, remove one of every 5 or 6 canes. In following years, remove up to 20 percent of the wood until new cane growth occurs. Select 2 or 3 new canes and continue to remove up to 20 percent of the oldest canes. Eventually, the bush will become more productive.
In old, poorly maintained plantings, some growers have had success cutting all the canes to ground level; harvest begins 3 years later. Others find that summer hedging immediately after harvest, coupled with selective dormant cane removal, works well.
Plants to be machine harvested should be pruned to a more upright habit with a narrow crown to allow close fitting of catcher plates and minimize fruit loss. Remove low growth that dropping below the height of catcher plates when loaded with fruit.
For hand harvest, keep bushes within easy picking height and remove low-fruiting branches or canes. Rake prunings out of the field and burn them or use a flail mower to pulverize the canes.
The Oregon State University Extension Service video, VTP 002, “Pruning Highbush Blueberries…A Grower’s Guide” (see Bibliography), may be used as a guide or to train pruning crews.
This fact sheet is adapted from Oregon State University Extension Publication PNW215, Highbush Blueberry Production. The authors of Highbush Blueberry Production are – Oregon State University: Bernadine Strik, Glenn Fisher, John Hart, Russ Ingham, Diane Kaufman, Ross Penhallegon, Jay Pscheidt and Ray William; Washington State University: Charles Brun, M. Ahmedullah, Art Antonelli, Leonard Askham, Peter Bristow, Dyvon Havens, Bill Scheer, and Carl Shanks; University of Idaho: Dan Barney. PNW215, Highbush Blueberry Production can be purchased from the Department of Extension & Experiment Station Communications, Oregon State University. How to Order