When it comes to pruning evergreens, a more accurate term would be whacking back evergreens. 

It is one of the most frustrating and misunderstood areas of gardening. We tend to wait until they become overgrown, and then we hope we can rejuvenate them somehow by cutting them back into old wood.

The longevity of a plant is partially determined by how well a plant has been pruned over the years. Most evergreens need pruning yearly to stay within the size and scale of most landscapes. 

Evergreens come in all different shapes and sizes — spreading, rounded, upright, horizontal and weeping. The natural branching pattern of the plant dictates its shape. 

By respecting this inherent form when pruning, it is possible to limit the size of the plant without changing its form. 

Not only does this preserve the plant’s true beauty, but it saves the expense of replacing an overgrown plant before its time is over.

Facts about evergreens

Knowing the science behind how an evergreen grows will help you understand the proper ways to prune them.

• Because evergreens retain their foliage year-round, they compensate for this by losing their oldest growth every year. Evergreens will usually hang on to their needles or leaves for three to five seasons. This is why you see the center growth on all evergreens turn yellow or brown in the center late summer.
• Unlike deciduous trees and shrubs, most evergreens will not rejuvenate themselves if cut back to old, bare wood.  Yews are the main exception. Most evergreens grow primarily from buds set the previous year and have few, if any, latent buds. It is generally safe to prune back only to one or two-year-old growth, which still has existing buds.  
• It is almost impossible to rejuvenate an old, overgrown evergreen. Therefore, it is important to prune on a yearly basis and not wait until the shrub or tree has become too large. 
• The best time to prune most evergreens is after the new growth has emerged, late spring to early summer. On most evergreens, the new growth emerges a lighter colour. Once the colour has faded to the older growth would be the best time to shear.
• To keep a shrub looking more natural, make individual cuts with the secateurs and not with the shears.
• To achieve a more formal, sheared, geometric look, shear up to three-quarters of the newest growth each year.
• Most evergreens will push out new growth twice in a season: Late spring and again in late summer. You could do a second pruning at this latter time, but not too late into the fall, because it will stimulate new growth that will not have time to harden off before winter.
• Always make sure that your pruners are clean and sharp, or it may cause a brown cast after shearing. Never prune your evergreens on an extremely hot, dry day, or the exposed undergrowth may burn.

When pruning any plant, it is always good to know what your goal is, which will help you determine how to best prune your shrub. Here are the two main goals of pruning evergreens:

1. Control the plant’s size

The best way to control the size of a plant is by natural pruning. Natural pruning means that you are making selective cuts to thin or reduce the overall size of the plant. 

This cannot be done with shears, but with secateurs or loppers. This means cutting one stem at a time and not just shearing off the tips to the same length. 

If you shear them continually, they will take on the form of a blob and lose its natural form.  

2. Maintain a certain shape

One of the goals of pruning might be to maintain a certain shape, such as a hedge, a pyramidal evergreen, a globe form or specimen plants like spirals and pompons. This is best achieved by shearing.

With shearing, you are just removing new tip growth, creating a full, dense look.

Even though electric shears make the job easier, hand shears make a much nicer job of things. Electric shears just tear the plant tissue, while hand shears make a cleaner cut. 

When the plant tissue is torn, there is more dieback at the tips, giving the sheared shrub a brownish tinge. 

Always make sure that any pruning tool is sharp and clean before use to prevent this from happening.

Joanne Young is a Niagara-on-the-Lake garden expert and coach. See her website at joanneyoung.ca.

The Niagara-on-the-Lake Horticultural Society is pleased to be hosting a series of Saturday morning gardening classes, available to the public. They will be facilitated by Joanne Young on Saturday mornings. Join us for the last seminar of the series this coming Saturday at 10 a.m. at the NOTL Community Centre. 

May 31 — Tough Plants for Tough Places

To pre-register for the classes, visit notlhortsociety.com/classes.