To PRUNE, or not to PRUNE, that is the Question

Many of my customers ask questions concerning landscape maintenance and pruning specifically. The decision for pruning is dependent on a range of factors. Some examples are:  What are the homeowner's goal for the plant, versus, what are the varieties of the material and the ultimate size required to maintain its health?

In most cases, it is best to prune a tree or shrub in the late winter or early spring before new growth occurs. However, there are other things to consider. Let's take a look at when you SHOULD, and conversely when you SHOULD NOT prune your plant material.

When you SHOULD prune

Picture courtesy of Kevin Tuck, www.rgbstock.com

Picture courtesy of Kevin Tuck, www.rgbstock.com

1. To maintain the size of the shrub in a neater appearance: 

I never encourage severely pruning a tree or shrub, since that can cause decline or death of the plant. If you have chosen appropriate plant material for the area in question, hard pruning should not be necessary. At that time, you can do gentle interior (selectively thinning of the interior) pruning to reduce the size of the plant and neaten its appearance. Most shrubs only require one pruning a year, and many do not require pruning at all.

2. To encourage new growth and flowering:

Pruning always encourages new growth of the plant. You can use this to your advantage in several ways. One example is pruning a shrub that has gotten 'leggy' to encourage new, fuller growth. Cutting out dead wood also encourages new growth from the interior of the plant.

For pruning to encourage flowering, you will first need to know if the shrub blooms on 'old' or 'new' wood. Plants flowering on 'new Wood' form their buds on the current year's growth. Pruning shrubs blooming on 'new wood' will encourage new growth and more flowering.  Pruning flowering shrubs on 'old wood' should occur immediately after flowering. You will also need to know when the shrub or tree blooms for proper pruning.

Here are some basic rules on when to prune flowering shrubs:

  • Prune spring flowering shrubs immediately after flowering: many spring flowering shrubs set their flower buds the year before (on 'old wood' see above.) You should not prune before they bloom because you will remove the flower buds and will miss a season of flowers.
  • Prune summer flowering trees and shrubs in late winter: Many of them bloom on 'new wood' and thus need to be pruned in the winter.The wild card in this process is the pruning requirements of Hydrangeas. For those shrubs, you will need to know if they are the macrophylla or quercifolia varieties, since they bloom on 'old wood.' If they are the paniclata or arborescens varieties, they bloom on 'new wood.'
  • Prune most broad-leafed evergreens at any time: Evergreens that do not have a noteworthy flower to consider can be pruned just about any time. Do use caution, however, when pruning needled evergreens, as most of their branches form from a 'candle' that emerges from the end of the stalk. Removing these candles can cause a stub to form and retard the growth of the tree.

When you SHOULD NOT prune

Photo courtesy of Kevin Tuck, http://www.rgbstock.com

Photo courtesy of Kevin Tuck, http://www.rgbstock.com

1. Because you want a large shrub to assume a smaller shape than is healthy for the plant: 
Many times, homeowners want to prune a normally 8' tall shrub and want to maintain it at a 2' or 3' height. Not only is this not possible for the long haul, but it will cause the decline or death of the plant. I would only prune a shrub by 1/3 its size, from the interior, to keep it healthy. I never recommend using shears to prune plant material.

2. Because you want to prune trees or shrubs down to two stalks: Hard pruning or 'topping' of some trees is not a suggested practice. Here in the south, I often see the practice 'Crape Murder' in the way that Crape Myrtles are pruned down to one or two stalks, with the canopy completely removed. This practice will cause extreme stress on the tree and ultimately cause decline.  Proper pruning only includes removing selective branches from the interior, remove suckers and gently pruning the canopy.

PRUNING TECHNIQUES: There are some techniques you will want to acquaint yourself with before you begin pruning. Here is a great guide:
http://content.ces.ncsu.edu/general-pruning-techniques.pdf

MORE INFORMATION:
NC State Extension Service also has a great pruning guide; it contains when to prune the most widely used trees and shrubs. You can take a look at it here:

About the Author:

Lori Hawkins, RLA, ASLA has been a registered landscape architect and active in the landscape design/build industry for over 30 years. Her service area includes Greensboro, High Point, Oak Ridge, Winston-Salem, Chapel Hill and the Raleigh NC metro areas. For additional inspiring project pictures, design ideas, or great garden gifts, take a look at these websites:

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