Features Production Research
Pruning for big cherries in B.C.

Consumer demand for the regular-sized sweet cherry has been changing
over the past few years, says Lindsay Hainstock.

Consumers are demanding larger-size cherries and the way to produce them is through variety selection, plus a little know-how with a pair of pruning shears, says Lindsay Hainstock, Oliver, B.C.

Consumer demand for the regular-sized sweet cherry has been changing over the past few years, says Lindsay Hainstock of Okanagan Tree Fruit Cooperative, Oliver, B.C. The market is now demanding big cherries, and B.C. growers have some of them the size of ping-pong balls.

Since 2003, nearly 89 per cent of the cherry trees planted in B.C. have originated from the Pacific Agriculture Research Centre’s Summerland breeding program, with the majority of orchards being planted with Lapins, Sweetheart and Staccato plus some early producing varieties.

While consumers are demanding bigger cherries, the larger varieties are also proving more profitable for growers to produce, particularly those using orchard management systems that produce nine and a half row sized fruit.

While variety selection is an important determinant in cherry size and shape, proper pruning is the deciding factor in just how big the cherries will be, says Hainstock. She advises growers and pruning crews to stand back and assess each tree before making the first cut. Choose three big cuts, removing big, older wood – the younger the wood, the larger the cherries – and start cutting at the top, shaping your way down, she adds. When pruning, growers might want to consider the “water flow” theory when making branch cuts, Hainstock says. According to this theory, water will flow to the biggest pipe first or, in the case of cherry trees, the biggest branch. She adds that growers in Washington state prune out what they call the “wood of mass domination.” Whichever way you want to think of it, “just try to balance out that flow throughout the tree,” says Hainstock.

Attention should be paid to obtaining and maintaining good branch crotch angles. A flat branch, jutting out at 90 degrees from the trunk, is more prone to break when laden with fruit than a branch with a slight upward, but not steep, angle, says Hainstock. She recommends using toothpicks or spreaders on young wood to help train and develop good crotch angles.

As for where to prune, Hainstock suggests cutting to the trunk if a branch is too strong or upright. Cutting to a stub will help to increase the number of fruiting branches, she says, adding that weaker tree branches can be strengthened by cutting the tips.

As for when to prune, Hainstock likes pruning during the late B.C. summer as a complement to regular winter pruning and knows of one grower who harvests his crop and then prunes afterward. “Consider the tree like a wound-up spring in winter just ready to pop,” she says, referring to the growth potential of the tree. “Consider it sprung in summer.” By pruning in the summer months, growers can help to control growth in vigorous plantings, says Hainstock, adding branches are usually softer and easier to prune in summer.

Summer pruning can also assist with light distribution within the tree canopy. Good sunlight distribution throughout the tree is very important and improves fruit quality, yield and bud quality. “You may have to change the shape around the main leader to keep light through to the centre,” Hainstock says, adding this can be accomplished by removing some of the tree’s inner branches, which will increase airflow and help to decrease pressure from disease. “Again, go with three cuts … and don’t get greedy for crop. You don’t want a tree overloaded with fruit,” she says.

Managing crop load is another goal that can be achieved by pruning, says Hainstock. Growers can reduce fruit load by pruning out branches but can also thin out the blossoms and the fruit if needed, something that may be necessary with new dwarfing rootstocks. “We are finding that we need to prune much more aggressively in trees on the new Gisela dwarfing rootstocks compared to trees on the standard rootstocks like Mazzard,” says Hainstock.

“Base your pruning on the tree’s vigour,” she suggests. “The tree has limited resources so balance it as best as you can with the fruit. There is an inverse relationship between fruit size and crop load.” Growers should consider the tree’s leaf to bud ratio and its distribution.
 
Contemplate how that tree will look three years down the road and balance the need for renewal wood with the current year’s cropping wood.

“Don’t bonsai the tree,” says Hainstock. “It may look great but it won’t produce any fruit.

“If you overcrop the tree, you’ll get zip, zero from it the next year,” she cautions. Growers should avoid heavy croppers, and know their varieties, especially the dwarfing ones.

Of the dwarfs, Hainstock notes that Staccato on dwarfing rootstock can be sensitive to bud damage and care must be taken during pruning. Based on research out of Washington state, Gisela 6 rootstock may require a support system after six years of growth, she adds.

Of the planting styles currently in use in B.C., Hainstock says it is popular to plant whips and delay the heading cut in the planting year until around the time the trees would typically be in bloom. The whips should be watered at planting but shouldn’t need any further irrigation until green growth is seen or the soil is dry down one foot, she says. If growers think they can add fruit size through irrigation, they should think again.

“It (irrigation) won’t help size, so it’s best to plant them, go fishing and not worry about them,” Hainstock concludes. ❦