Dormant pruning techniques have been honed by orchardists, many of whom take pride in the art that goes along with the science of pruning. Dormant pruning, at many orchards, has been approached with reverence, as growers develop their unique takes on just how to shape and manage their trees to produce the best quality and a good quantity of fruit each season.
John Esslinger, Penn State Extension horticulture educator, recently took growers to the fields to demonstrate proper winter pruning techniques for apple trees. The workshop covered the traditional central leader, medium-density orchards common in the region, as well as tall spindle trees in high-density orchards.
“Dormant pruning has several benefits,” Esslinger said. “Simply put, it focuses the tree’s energy into producing quality fruit. It does that by developing the tree into a structure that maximizes light penetration throughout the entire tree, and promotes an even crop year in and year out. The goal is the same for both pome and stone fruits.”
Prune for production
Dormant pruning is the key tool to enhance light penetration through the tree canopy, and optimize it to produce fruit. Pruning cuts help to determine the amount of fruit that will be produced and impact the quality of that fruit. Light penetration into the tree determines the amount of fruit that will develop. The distribution of that light throughout the tree establishes fruit location and quality. Depending on the type of tree, fruit is produced on spurs, which develop on older branches, or on new limbs. Various types of fruit trees have spurs that remain fruit bearing for different amounts of time. Dormant pruning helps to control the amount of fruiting that can occur. Pruning out less productive spurs, or thinning spurs where too many exist for optimal fruit quality, are goals, helping to maximize light and balance fruit load.
“Young trees need less and less structural pruning as they develop,” Esslinger said. “Once the tree is developed, the goal is to keep the tree relatively open and promote young branches. Young wood is more productive than old wood.”
As trees age, their tops become heavy. This limits the amount of fruit-bearing occurring on lower limbs. Keeping the tops of the trees weak, via selective dormant pruning, promotes fruiting on the lower branches. An open canopy, with light penetration, also makes a less conducive environment for diseases.
Two types of cuts are heading cuts and thinning cuts, and fruit trees respond differently to each. Generally, heading cuts are used to train young trees, or renew older trees, and cause a greater response in growth. Thinning cuts are used annually to keep trees in optimal production.
Thinning cuts remove entire branches, limbs or shoots. These increase canopy light penetration and direct energy into fruit growth. These cuts are used in trees of all ages to influence production, either by suppressing it or causing it.
Cut with care
Don’t make cuts unless the weather is going to cooperate. The biggest danger is pruning, then having a cold spell hit, leaving the trees susceptible to winter injury. Although it may be tempting to prune during that inevitable midwinter warmup, waiting until the weather is most likely to remain moderate in the long term is best. Pruning can reduce fruit tree cold tolerance, making them more susceptible to cold injury for a week or more following the process.
“If we prune during a 60-degree day warmup in January, which is then followed by near zero temperatures a few days later, we can see severe injury to trees pruned during the warm spell,” Esslinger said.
Pruning creates a wound on the tree, and disease-causing organisms can enter the wound. Wet weather during pruning can also lead to diseases. If the weather is too warm when pruning occurs, insect activity will increase, along with a better chance that pests can gain access via pruning cuts.
Dead branches, branches that overlap and cross over each other, those that rub together, and branches that inhibit an open canopy are all pruned out during the dormant season. Too much pruning, though, can cause vegetative growth and reduce the season’s fruit yield.
Although today’s high-density orchards may not offer many opportunities for individualized pruning strategies, they do need to be dormant pruned. Doing so helps achieve the very open tree form, which causes a highly productive tree, yielding high-quality fruits.
“Pruning is still very important,” to high-density orchards, Esslinger said. “The new, high-density plantings require lots of small branches that are then removed when they become too large. When the larger limbs are removed, the tree is more prone to develop replacement limbs.”
A “pruning by the numbers,” simplified approach has been designed for very high-density orchards planted on dwarfing rootstocks. In this technique, a branch is pruned as soon as it reaches a specified diameter. Younger branches can then fill in the area, and the cycle continues, keeping fruit production optimized.
“The system both promotes and allows younger shoots to develop into renewed branches,” Esslinger said.
If that simplified system of pruning isn’t enough, high-density orchard dormant pruning is on its way to automation.
“The high density plantings develop a more uniform canopy that resembles a hedge,” Esslinger said. “Uniformity is a key component that allows the development of automated machinery so workers can get more done in less time.”
Pruning is a lifelong necessity for fruit trees. When young, dormant pruning primarily controls vigor and directs energy into fruit production. As trees age, dormant pruning helps to promote continual fruiting. Late-winter dormant pruning, done properly, allows trees to heal quickly as the end of the dormant season approaches. Sharp tools and clean cuts are key, whether your trees are planted old-school, new wave or something in between.