Knowing the right times to prune trees and shrubs is a key part of your yearly landscape maintenance. Pruning is essential in order to keep your woody ornamentals growing in the desired shape and free of dead limbs. Additionally, certain types of plants will flower more when pruned correctly. It is important to prune consistently every year to avoid allowing undesirable limbs to continue growing.
Late winter, at the end of the dormant season, is generally the best time to prune most trees and shrubs. When pruning takes place between February and early April, the wounds on the plant are only open for a short time before new growth occurs and begins to seal them. On deciduous trees and shrubs, it is also much easier to see the overall shape of the branches when they have no leaves. For many plants, pruning during the spring and summer can promote disease. One example of this is many trees and shrubs in the Rosacea genus, such as crabapples, may suffer from fireblight that is spread through pruning during the growing season.
While dormant season pruning is best for most woody plants, it is not always the best time to prune. Early-blooming trees and shrubs, such as ornamental plum or cherry, blooms on the previous year’s growth. These types of plants should never be pruned in the dormant season if flowers are desired. Instead, they should be pruned as soon as they are done blooming in order to promote the new growth that will produce blossoms the following year.
Hedge shrubs often times need a couple prunings per year to promote uniform, dense foliage. While simply shaping the plant with hedge trimmers is needed to maintain the desired shape, many times this is not enough to achieve a thick layer of foliage. Large, overgrown branches can often lead to bare spots in the hedge. In late winter or early spring, remove approximately one third of the oldest, thickest branches all the way to the ground in order to promote new growth. For severely overgrown deciduous hedges with multiple stems (cane-growth habit), another option is to cut all of the canes down to the ground. The plant may take a year or two to regrow, but this allows for a fresh start to shape the hedge properly.
Using the proper equipment is very important when pruning in order to avoid damage to your plants. Hand pruners may be used to make cuts up to 3/4 inch in diameter. If you can’t make the cut using only one hand on the pruners, you should probably be using a different tool. Lopping shears are the ideal tool for cuts of 3/4 to 1 and 1/2 inches. Larger branches should be removed using a saw or chainsaw. Make sure to take care of your tools by cleaning them after use and sharpening as needed. This will make your job of pruning easier as well as extending the life of the tool.
Source: https://www.extension.umn.edu/garden/yard-garden/trees-shrubs/pruning-trees-shrubs/