Pruning should focus on needs of the bush

LANGLEY – Pruning blueberry plants is all about balance.

In young plants, that means balancing vegetative growth with root growth. In fruiting bushes, it’s about balancing vegetative growth with yield and berry quality.

“You want to try to maximize your canopy growth,” says Lisa Wasko DeVetter, who leads the state-wide small fruit horticulture program at Washington State University in Mount Vernon, Washington. “We all do it a little different. I’m always thinking, what are the first good cuts I can make to improve the bush?”

Wasko DeVetter proceeded to show a cluster of growers her approach to pruning a bush in a field of Duke blueberries planted in 2021 at Driediger Farms in Langley, on February 1.

Nearby, Tom Stewart, production manager for the Pacific Northwest with Driscoll’s, was demonstrating his pruning techniques to another group of growers.

“It’s not the end of the world if canopies cross over a little bit,” he says, demonstrating that diversity in pruning techniques is not necessarily a bad thing.

Most important, pruning must reflect the needs of the plant.

Stewart said mature plants require separation to ensure proper air flow through the plants, something pruning that keeps the crown narrow with more upright branches facilitates. Pruning isn’t so much about shaping the bush as it is about creating a more efficient plant with the right kinds of growth.

“I would take this one down to three or four canes,” Stewart says of a Calypso bush planted last year. “Cut the other [whips or branches] down to the crown. You can really make these young plants just look like stubs. They will grow lots more back.”

When the plant is young, removing more canes to ensure the plant’s energy is focused in the roots as well as three to four remaining canes is important. Selecting and continuing with four to six canes is the standard for pruning upright branches once the plant matures. The canes with the largest diameter will produce the largest fruit.

Wasko DeVetter added that humic acid can be a helpful amendment that stimulates more root growth in plants up to about three years old. As a fertilizer, humic acid isn’t the be-all and end-all for young blueberries, but it can be especially helpful in sub-optimal soils.

Suwinder Kaur Jassal and her husband Baaz Singh Jassal own B&J Farms in Abbotsford with 2.5 acres of Duke and were among the 40 growers who attended the workshop.

“I came just to see how I’m pruning the right way or wrong way,” she says. “I guess I’m doing okay.”

Jassal and her husband do the pruning on their own. They’d hired the job out once in the past and the bushes were taken back so far there was no fruit that summer. She prefers to manage the task on her own now.

“Would you take that one out?” she asks Stewart, who agrees with her suggestion to cut off a branch sticking into the alley between rows of bushes.

Jassal explains that the need to keep the bush crowns narrow is about efficient picking – both by machine and by hand. If branches extend out from the crown and are more horizontal than vertical, the weight of the berries will pull the branch down and make it harder on pickers who would have to stoop lower. Those weighted branches may also leave berries resting on the mulch around the plants, which is undesirable, she says.

Additionally, as branches extend into the alley, they create resistance for the catching plates on mechanical harvesters. The plates can’t get close enough to the plant and berries subsequently fall through the wider gap onto the ground.

“You want to get rid of the stuff that’s growing out into the centre and break off the weak laterals that aren’t going to give you good fruit,” confirms Wasko DeVetter.

Wasko DeVetter adds that it’s important to remove any twiggy branches as these will limit plant growth and sap fruit production energy without providing returns. Duke in particular tends to produce a number of twiggy dead-end branches, but taking each one off uses up labour, so growers must know the best methods for their varieties and teach those to pruners if not doing the work themselves.

Wasko DeVetter says a plant can shift without annual pruning and some plants are more susceptible to changing their orientation than others.

While she’s been involved in berries for a number of years and is very aware of pruning practices, February’s event was her first pruning workshop.

Wasko DeVetter is succeeding Bernadine Strik, long considered Oregon’s berry goddess. Strik retired in 2021 and passed away in May 2023 after 34 years as a professor at Oregon State University and berry crop research program leader.

Strik led the way in grower education that changed the industry.

She suggested that annual pruning, always in the winter, made for better crops. Too little pruning would lead to small fruit and limited growth, while too much would result in large but fewer berries. She believed pruning too lightly was often where growers erred rather than over-pruning.

“You can certainly do more and try to make it perfect,” Wasko DeVetter says. “You can spend a lot of time on a bush, but focus on the most important things.”

She says it’s wise to cut low, less productive branches in order to encourage more upright growth. A general rule of thumb is to take about 30% of a mature fruiting plant’s branches in annual pruning to encourage root, shoot and fruit growth.

Pruning also helps ensure fruit set and seed set.

Removing the tip of fruiting branches can help increase fruit size. Leaving too many buds can delay fruit maturity and stretch yields over a longer season.