News & Events

An Update from Tegwen

May 22, 2023

Pruning – Why do we prune plants?

 

When we prune we make a wound. This is a fundamental aspect of pruning. I’d like to begin this chat with this simple detail as the basis for thinking about why and how we might prune plants. If we don’t think about why and how we prune plants we run the risk of falling into what I consider the three most problematic issues that lead to improper pruning. The first issue is pruning without a goal; the second is planting trees or shrubs in the wrong place; and the third being lack of knowledge concerning the correct pruning techniques. If these three points are ill-considered, then they increase the risk of plants either succumbing to pest and disease attacks or suffering from the ingress of decay, eventually leading to death.

 

1.Pruning without a goal

Sometimes when pruning is done without a plan in mind, it can end up doing irreversible damage to trees and shrubs. If we accept that pruning itself is injurious to the plants that are in our care, then at the simplest level the goal of pruning needs to ensure that our cuts to plants are made with the aim to promote vigorous healthy growth that is free of structural weakness and minimizes the risk of being attacked by pests or infected with disease. With this in mind, together with the correct techniques (see below) our approach to pruning can be quite uncomplicated if the outcome is simply to promote and enhance the health and natural shape of the plant.

Pruning decisions get more tricky when our competing aesthetic values are taken into account. Some people prefer immaculate formal gardens in which each plant is tightly clipped into a precise symmetrical shape. Others may see these garden styles as desolate, contorted and lacking natural abundance and vigor. Alternatively, whereas some appreciate a ‘wildness’ in their gardens where natural and sometimes unpredictable growth habits are left to develop, others just see untidiness and disorder. When we have competing preferences like these and there is an impasse regarding how to prune, I like the idea of letting the plant decide. It’s here that we need to appreciate the plant’s habit for what it is and return to our goal of pruning for plant health. If this settlement is unsatisfactory, then we need to turn our focus onto the importance of plant choice.

 

2. Planting the wrong plant in the wrong place

Plant choice is crucial when trying to avoid unnecessary, improper and remedial pruning. We’ve all seen what happens to a majestic London Plane tree, for example, that has been planted under power lines. Its natural pyramidal shape is often destroyed by removing the central leader and limbs to accommodate the lines. Another example of poor plant choice is when shrubs that have been planted too close to paths. They are often pruned back so hard and so often that the wood no longer has any nodes left to be able to regenerate. The result usually looks like an unsightly bunch of sticks with leaves growing on top. You do have a wider variety of plant choices if you have access to additional time and expert knowledge in terms of advanced pruning techniques such as coppicing, pollarding, pleaching, topiary and espalier. For example, you would be confident when planting a pear tree right next to a wall if you knew how to espalier. However, it’s rare that we have the luxury of hindsight when it comes to planning our gardens. We often inherit the choices of others. And when we do we need to know how to prune properly to maintain the health, vigor and shape of the plant.

 

3. Correct pruning techniques

Trees

Generally all we really need to do to prune trees is to remove dead, damaged or crossing branches. How we make the cuts to remove these branches is important. When cutting trees, as with any plant it is good practice to make sure that you have the right tool for the job and that it is sharp. Dull tools can do significant damage. They can rip, shred or mash the bark causing larger wounds than necessary. Please contact us if you think you don’t have the right tool for the job, particularly if the plant is encroaching on a path. Breaking off limbs and twigs damages the plant as well as leaving behind unsightly and sometimes more dangerous sticks that jut into the path.

 

Making cuts

When removing a tree limb you should never cut flush to the trunk. This removes the branch collar (the slight swelling at the base of the limb) that is needed to facilitate wound healing. Alternatively, leaving a stub leaves too much dead branch on the tree which may decay backward into the trunk. If the bench collar is difficult to find, start the cut on top of the branch 2-3com away from the crotch, making a gently angled cut slightly away from the main branch or trunk.

Do not heavily prune trees in summer or over prune trees any time of the year. Doing so  reduces the trees photosynthetic capacity and protective functions in terms of heat and pest and disease resistance.

Do not top a tree. Topping is just cutting the top off a tree and often happens when it’s planted in a confined space or people attempt to restrict the tree’s growth for aesthetic purposes. It is a practice to avoid because the new growth is vigorous, unsightly and structurally weak. The cuts made do not have branch collars so the tree is vulnerable to rot. If possible, it’s better work on selective branch removal to improve structure. The practice of thinning reduces weight on heavy limbs and helps retain the tree’s natural shape

 

Pruning shrubs and hedging

When cutting shrubs using secateurs or loppers it’s best to make clean slanting cuts, ideally made just above a bud, at a fork on a branch or just beyond the branch collar. Most shrubs, including natives, will respond well to pruning and trimming. When using an electric hedge trimmer to shape shrubs and hedges take care that the machine is not cutting beyond the appropriate branch thickness. It may rip branches rather than cut leaves.  However, it should be noted that how often shrubs get pruned, indeed if at all, is dependent on the interaction between the following factors: the species, desired aesthetics, time of year, health of the plant and environmental conditions.

A note on cleaning up – Pruning can sometimes be quite physically demanding. Get out and have a go but be mindful of  biting off more than you can chew. With this in mind, have a green bin open next to you so you can clean up plant debris and cuttings as you go. Leaving a pile on the ground can encourage pests and diseases.

 

Correct pruning technique – the callous will continue to grow over the pruning cut. 

 

Improper pruning technique – branches are cut too far away from the collar.

 

Formative pruning of a Loquat tree to enhance natural habit.

 

Acacia – crown lifted by removing the dense growth and crossing branches. 

 

Happy pruning!

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