As gardeners, we prune our trees and shrubs for many reasons. We prune to control shape and direction of growth. We also prune to open the interior of our trees and shrubs to allow more light penetration, better air circulation, and to create an airy feel to their structure. Most importantly, we prune to remove dead, diseased, or damaged plant tissue.
Generally, it is best to prune trees in the dormant season, typically in the late winter months; however, dead, diseased, or damaged wood should always be removed as soon as it is discovered.
Although dormant pruning is often recommended, many trees and shrubs benefit from summer pruning.
Summer pruning can help to control tree growth as well as greatly reduce the need for dormant pruning to maintain a desired shape. Since dormant pruning (pruning in the winter months) seems to encourage growth, summer is a great time to start trying to tame and reshape your overgrown trees.
Prune deciduous trees around midsummer.
This will minimize sap loss caused by pruning too early in the season. In addition, trees pruned earlier than this, as in late spring/early summer, may actually experience a burst of growth, which would defeat the purpose of your shaping cuts!
Avoid pruning after the end of July, however, since the scars, as well as any new shoots that the tree produces, may not be hardened before the cold of winter and will be more prone to frost damage and winter injury.
Watersprouts and suckers are shoots or branches that grow vigorously straight up from the base, lower trunk, or scaffold branches of the tree. These should always be removed with hand shears when they appear as they sap energy from the tree and also give it an unkempt appearance.
Fruit trees also benefit from summer pruning/thinning. By removing excess, non-fruiting branches (i.e. thinning), more nutrients can be channeled to the ripening fruit increasing their quality. Thinning allows more light to reach the fruit which leads to improved fruit color. Thinning also increases air circulation through the trees which can help reduce certain diseases that thrive in stagnant air.
Never thin more than 20% of the growth in one season.
Just like trees, summer pruning of shrubs can help to curb plant growth. Vigorous evergreen shrubs like cherry laurel and yews that have outgrown their space in the garden should be cut back in the late spring or early summer.
Shrubs that flower in the first half of the year, such as rhododendron, azalea, forsythia, lilacs, and weigela, should be pruned soon after they finish flowering. These shrubs flower on "old" wood, or wood that was made in the previous season. When you prune, it encourages the development of new growth, increasing the amount of flowering wood for the next year. Once these shrubs are established, you can prune out a third of the older flowering wood, keeping a balanced shape in mind. Pruning must be done early enough to allow the shrub's new flowering wood to harden off before winter.