Why should you summer prune? There are many benefits to summer pruning including increasing fruit color, reducing vigor, and most importantly reduce the amount of winter pruning (although summer pruning is not a replacement for winter pruning, but rather a complement!). In the last few years, new research on mechanical summer pruning in apples has shown that pruning small diameter weak wood can result in an increase in flower buds on the end of the regrowth. However, I want to highlight that this only happens when mechanical summer pruning is done on calm trees, on dwarfing rootstocks with small diameter fruiting branches, and you would not get these results if you are mechanically summer pruning larger trees on vigorous rootstocks and cutting back large diameter branches.
When is the best time to summer prune? Ideally you would wait until the shoots stop growing and a terminal bud forms, which will prevent the regrowth of multiple shoots near the cut (i.e., witches’ broom). Research in New York state testing mechanical summer pruning in 1-yr old shoots with 15 leaves in June, July, and August did not result in vigorous regrowth. Shoots prune in June and July resulted in new regrowth of 8 and 5 inches, respectively, and with a terminal flower bud, while the August timing resulted in no regrowth. Waiting as late as possible to summer prune is probably the best option, considering that early summer pruning will expose fruit that might experience sunburn damage, and that those exposed fruits would also get more damage if there is a hailstorm.
Earlier cultivars should be prune before late maturing cultivars. The timing of mechanical summer pruning for cultivars that produce large size fruit, such as Honeycrisp, should be earlier that those that produce smaller size fruit, such as Gala. Timing of fruit maturity should also be considered, as cultivars with earlier maturing fruit will stop shoot growth earlier and can be mechanically summer prune before late harvesting cultivars.
How much of the shoot should be removed? If the objective of the summer pruning is to increase sunlight in the canopy to enhance color development, then pruning should be limited to remove shoots that block light to the fruit. Excessive summer pruning will debilitate the trees because it removed too many leaves that produce carbohydrates to grow and ripe the fruit. If the objective is to reduce the vigor of the trees, then you should cut back to weak side branches or to a fruiting spur in 2 yr old wood.
How about summer pruning young trees? It is not recommended to summer prune trees that have not filled their space yet. The reason for this is that removing leaves and shoots during the summer will reduce tree growth and the tree will take longer to fill their space, thus setting you back on the goal of achieve maximum yield potential in the shortest amount of time.This article was posted in Apples, WFN and tagged Apples, Pruning, summer pruning.