Improving Shrub Health by Pruning

By Nate Dalman, Horticulture Researcher II

September 2019

When thinking of why to prune shrubs, many people would say the main reason is to manage the shape and appearance of the plant. However, that is just one out of a long list of beneficial reasons to keep up on pruning. Other benefits include the plant producing more flowers, have a healthier and more vibrant leaf color, higher tolerance to damage and removal of unhealthy biomass. 

Removing some of the branches or reducing the size of a shrub causes it to produce new shoots. These young shoots are fast growing and are visibly healthier than the older growth. This leads to the more luscious leaf color and increase in the number of flowers since nutrients can be more efficiently transported from the roots to these young shoots. It is important to note that the increase in blooms may take two or three years depending on how much biomass is removed from the plant but the new shoots will begin growing the first year. This new growth is also going to be less likely to be affected by disease than older growth and can recover from damage faster than old growth. 

The best time to prune shrubs is typically late winter to early spring. This way the open wounds on the plant will only be exposed for a short time period before growth resumes. Shrubs that produce flowers from the previous year’s growth can also be pruned after they bloom and that way the plant has enough time to regrow before flowering again. 

When pruning to improve plant health, all dead or sick wood should be the first to be removed, being cut all the way to the base. The next branches to be removed should be those that are overgrown and crossed or intertwined. After that, branch removal can be determine by the desired shape and size. A good rule of thumb is never remove more than half of the shrub’s biomass. 

Large overgrown shrubs can easily be rejuvenated by removing one third of the largest and oldest branches each year. The roots will then produce new shoots and this cycle can be repeated each year or every other year until all of the large overgrown branches have been removed. After the shrub has been rejuvenated, pruning should be maintained to prevent the shrub from becoming overgrown again.