Part 2 of Pruning Modern Landscape Plants
By Todd Layt
Understanding how to correctly prune trees is a lot more complicated than pruning the smaller plants as shown in part one of this article. Get pruning a small plant wrong, and the plant can be harmed. Get pruning a tree wrong; life and property can be devastated. That’s why part two of this article comes with an important disclaimer. This is more about pruning trees when they are small, and not large. That should be done by an expert, but even small trees need to be pruned correctly, otherwise they grow up to be dangerous big trees. If you are in any way unsure, seek professional advice.
Big trees can be made to look like shrubs or dense smaller trees by special pruning techniques. Sometimes it pays to consider coppicing and pollarding on some trees and even a few shrubs. If the plant is cut back close to the ground it is called coppicing. If that process takes place further up the trunk, then it’s called pollarding. For some tired old trees this can breathe life back into them. It can also make an average looking healthy tree look amazing.
The success rate of this type of operation depends on tree type. Some die easily, and others have high success rates. Coppicing can allow certain large or medium trees to be used in smaller gardens and landscapes. The fresh new foliage produced can be super clean and vibrant. This technique is regularly used for producing cut foliage. Pollarding needs to be done with far more care, as it can produce dangerous trees if they are let grow out in the future. Eucalyptus types such as pulverulenta, perriniana, cinerea, and cladoclayx have responded well to coppicing, providing beautiful green, silver grey to in the case of Vintage Red, even vivid red foliage.
The best time to coppice a tree is mid to late Spring, and in some regions summer. It’s best to make sure the tree is healthy and fertilised before attempting this. Most Australian native shrubs such as Calistemon do not like coppicing, but real research needs to be done on different species. I have had some success coppicing some Callistemon species, but lots of failures with others. Some Grevillea types for example also respond to pollarding. It is best to regularly prune these types of native shrubs and trees, although a hard prune via coppicing is sometimes the only option other than replanting. In this case what have you got to lose?
It’s important in pruning young trees to approach it more strategically. Correct pruning is preferable in developing a tree with a strong structure and desirable form. Trees that are appropriately pruned while they are young will require little corrective pruning when they mature, but how often is this really done? Hopefully the nursery supplying the tree has done most of the work. When buying advanced trees this is often the case and only minor corrective pruning will be needed. When planted from tubes or small pots, more corrective pruning maybe needed.
When pruning young or small trees remember each cut may change the growth of the tree, so have a purpose in mind. Correct technique is critical. Learn where to make the cut. When a tree is wounded, it must grow over the wound meaning the wound is contained within the tree forever. Small cuts do less damage to the tree than large cuts. Waiting to prune a tree until it is mature can create the need for large cuts that the tree cannot easily close, so it is a real benefit to shape the tree when small. When pruning to the main branch it is very important to make pruning cuts slightly away from the branch collar. When pruning on a branch where you want new growth to occur, prune just past the bud you want to reshoot. The closest bud will then regrow quickly.
Shaping a young tree for good future growth depends on a few factors. Firstly it is important to establish a strong scaffold structure. The scaffold branches provide the framework of the mature tree. Properly trained young trees will develop a strong structure that requires less corrective pruning as they mature. The goal in training young trees is to establish a strong trunk with sturdy, well-spaced branches. The strength of the branch structure depends on the relative sizes of the branches, the branch angles, and the spacing of the limbs. Naturally, those factors vary with the growth habit of the tree.
Good pruning techniques remove structurally weak branches while maintaining the natural form of the tree, and help keep the branches well-spaced. You basically want a well-balanced tree. Trunk development is also important. For most young trees, maintain a single dominant leader growing upward. Do not prune back the tip of this leader or allow secondary branches to outgrow the main leader. Sometimes, a tree will develop double leaders known as codominant stems. Codominant stems can lead to structural weaknesses, so it is best to remove or shorten one of the stems while the tree is young.
A tree’s secondary branches contribute to the development of a sturdy, well-tapered trunk. When numerous branches are being removed, it is preferable to retain some, at least temporarily, to promote trunk diameter growth. Permanent branch selection is important. Many branches present on a young tree at planting will be pruned away at maturity to provide clearance for mowing, pedestrians, and vehicle traffic. Screening trees usually have branches all the way to the ground; whereas trees that have vehicles going under them have branches ultimately cleared for the first 5 metres.
When pruning, be sure not to remove too many branches. Leaves and their supporting branches are major sites of food production and storage. Pruning of newly planted trees should be limited to the removal of dead or broken branches. All other pruning should be withheld until the second or third year, when a tree has recovered from the stress of transplanting.
Make sure you use the right tool for pruning trees. For small trees, most of the cuts can be made with hand pruning shears (secateurs). The cleaner more accurate cut of the scissor-type, or bypass blade hand pruners, are preferred over the anvil type. Ergonomic type pruning shears such as the ones sold by Felco make pruning much easier than the standard type. For serious tree pruning, you can’t go past the Felco power assisted electric models. Cuts larger than one-half inch in diameter should be made with lopping shears or a pruning saw. Never use hedge shears to prune a tree. Whatever tool you use, make sure it is kept clean and sharp.
Some of the information in this story came from a free PDF guide for pruning young trees from the International Society of Arboriculture
Nursery grown advanced trees in Australia are usually grown to a system called Natspec, which is a guide for specifying trees. If you want to really understand the pruning and staking of young trees in Australia try this guide. Happy pruning! LM