Now is the Time for Shrub Pruning

Kari Lewis, MSU Extension - Glacier County

Even though it hasn’t felt like spring much yet, the calendar says spring is right around the corner.  Now is the ideal time to prune many trees and shrubs as we commonly think of the late dormant season being when severe cold has passed, but new growth has not yet begun.  This dormant season pruning typically enhances the plant’s vigor, and will stimulate new growth.  In addition, pruning now will provide the trees and shrubs the entire growing season to recover.  This blog will focus on pruning shrubs, with information from the Montana Master Gardener Handbook.  

When a shrub flowers determines when is an appropriate time to prune that shrub.  Shrubs that bloom on current season’s growth which would be ok to prune now include Peegee hydrangea, potentilla, shrub rose, snowberry, and Hills of Snow bushes. 

One exception to pruning shrubs this time of year includes shrubs grown primarily for their flowers that that bloom in the spring.  Spring flowering shrubs are any shrubs that bloom at the same time or before the lilacs bloom.  These spring flowering shrubs bloom on LAST year’s growth, so should be pruned right after flowering.  Examples of these would be honeysuckle, rhododendron, lilac, and rambling rose bushes. 

Photo courtesy of Texas A&M Extension,
available at http://aggie-horticulture.tamu.edu/earthkind/
landscape/proper-pruning-techniques/

If you are wanting to prune shrubs into a hedge, small shrubs that are 1 to 3 years old should be cut back to about 3 to 5 inches above the ground to encourage growth of new shoots at the base.  If you have older shrubs that you would like to transition into a hedge, cut back one-third from their tops and sides to help develop a full, bushy hedge. 

The main thing to remember when pruning a hedge is that the ideal hedge is wider at the base than the top.  A hedge should look like a truncated cone shape. 

Often, I will see the exact opposite of this, that is, the top of the hedge is wider than the base.  This leads to thin, weak growth, as the wider top portion of the hedge shades the lower portion and without adequate sunlight to the lower portion of the hedge, it becomes less vigorous. 

Formal hedges should have one-third to one-fourth of their oldest branches near the ground cut back each year.  Upper branches of the hedge can also be cut back to their main parent stem to encourage fresh, new growth. 

If you prune any infected branches while pruning, make sure to clean your pruners with rubbing alcohol after each cut so that the pruners don’t transmit the disease to another portion of the hedge or to the tree you prune next. 

For questions on this topic, please contact Kari Lewis at kari.lewis@montana.edu.  Image courtesy of http://aggie-horticulture.tamu.edu/earthkind/landscape/proper-pruning-techniques/.