The country’s trees have taking quiet a bashing this year and many of us are still clearing up damaged and felled trees. We can make the best of it by stocking up the woodshed and plan some winter pruning while we’re at it. With some exceptions, most trees are pruned in winter anyways. This is largely because deciduous plants go dormant in the winter and so less stress is received by the plant. There are other reasons for winter pruning. All the energy of the plant has been drawn in to its roots in the winter. This means the plant will have a large reservoir of stored food coming into the growing season considering you have removed some of its upper mass. Also, with all the foliage gone, it’s far easier to see the shape and branch structure that you’re working with.
Be careful not to prune important plants such as fruit trees too early however – if the plant has not gone dormant then new growth will be stimulated leaving the plant weakened through the winter. This can mean waiting until after January considering the mild winters we’ve been having lately. Leaving pruning later, till early spring, also has the advantage of minimising the amount of time the wounds are exposed before new growth begins.
Reasons for Pruning
- Keep the plant healthy by removing dead, diseased or damaged material.
- As witnessed in the recent storms, strong winds will take many trees and their branches apart. Pruning back weak branches or those overhanging in undesirable/unsafe areas will minimise the risk when the next gales hit.
- Opening up trees by removing branches stops branches crowding together. This allows more air to circulate, which is important for reducing disease, and also allows a good level of light to reach the growing parts of the tree.
- A plant’s natural shape is on the whole its best expression. Tightly pruned trees and shrubs which are moulded into solid geometric forms perhaps serve only as an outward expression of our boxed in mentality. However, pruning can be used gently to control the size of a plant, play with its shape, and keep evergreens dense and nicely proportioned.
Fruit Trees and Pruning
Pruning is a much more important activity for fruit trees. Reasons more specific to fruit trees and bushes include:
- Controlling the height of the tree so that the fruit remains within reach.
- Preventing the spread of specific debilitating diseases.
- Developing the limb structure of the tree to create strength and allow air circulation.
- Encouraging the growth of new shoots which will bear fruit in future.
It is also important to remove pruned fruit tree material away from the site, especially if showing signs of disease, as the material may serve to carry the disease organism over to re-infect healthy new growth.
How Pruning Shapes a Tree or Plant
In simple terms, pruning works by playing with a process known as apical dominance. This is the tendency for the shoot or branch to grow predominantly from its tip. The bud at the tip, known as the apical bud, grows actively and lengthens the stem. It also produces additional secondary buds to the side of the stem which are left in its wake as it grows away. Leaves appear at these secondary lateral buds but the buds themselves often remain dormant. This dormancy is controlled by the hormones which the apical bud is producing as it grows. They flow back down the stem and inhibit the side buds from developing. The strength of apical dominance will vary between different species of plants.
When we decapitate the stem by pruning, and remove the apical bud, the hormones are also removed and the side buds closest to the cut wake up and begin to grow. This is why pruning a plant makes it get bushier and fill out, which is useful for creating hedging and windbreaks.
As the hormone (auxin) flows downwards with the pull of gravity, the angle of the shoot or limb will have a big influence on how it moves in and affects shoot growth. For example, an upright stem will lead to the strongest apical dominance compared to a stem at 45? which will have a more balanced growth habit with the lateral shoots growing at a similar rate to the apical growth. With a horizontal limb the effect of apical dominance is lost completely and vigorous upright shoots will take off from the top side. These are known as ‘water shoots’ and often a problem in fruit trees where the branches are kept horizontal to improve fruit production and access.
Apical dominance is probably the most fundamental and important principle to grasp when beginning pruning. However, there are of course a lot more factors which determine how a plant will react to pruning. For instance, the ratio of root to shoot mass after pruning and the particular growth habit or disease susceptibility of the species in question will have a big impact. These then have to be considered with the shape you are trying to achieve.
All these factors can amount to make pruning seem a bit daunting. Like all skills, there is no substitute for some hands on experience to get a grasp of the principles and gain some confidence. Practical pruning courses and demonstration are offered around the country and are well worthwhile so you can see real examples of the principles as you learn. Irish Seed Savers, who have been preserving Irish heritage fruit trees for years offer excellent courses and the The Organic Centre in Leitrim is another good place to start.
Tools for Pruning
Which tool to use for pruning depends on the diameter of the wood to be cut. Pruning tools range upwards in size from snips, hand pruners (secateurs), loppers and saws.
- Snips – These are useful for small plants, taking cuttings and deadheading. Deadheading is the practice of removing fading or dead flowers from plants. This keeps the plant looking tidy whilst encouraging more flowers to develop.
- Hand pruners/Secateurs – these are one of the most oft used (and oft lost) tool in a gardener's arsenal. Indispensible for a wide range of tasks from clearing brambles to pruning fruit trees and bushes. With pruners, there are two types to choose from: ‘Crosscut/Bypass’ pruners have blades which slide past each other like a scissors. These make sharp clean cuts and are used for pruning living tender stems. ‘Anvil’ pruners work by having a top blade which bites down into a flat base plate more like a knife on a chopping block. These are more forgiving than bypass pruners as they cut effectively even if the position of the blade moves during cutting. Less force is also required to make cuts so they are well suited to thicker material. They are usually used for cutting dry, hard or dead wood. Pruners are suitable for cuts up to 2.5cm.
- Loppers – larger two-handed versions of hand pruners specifically designed for the task of pruning thick branches that cannot be pruned comfortably with a one handed pruning shear and where a longer reach is needed. Also available with bypass or anvil blades. These are good for cuts up to 4cm.
- Saws – For cuts larger than 4cm a saw is required. They are also fine to use with smaller branches. Pruning saws usually have a large tooth pitch which makes cutting through fresh green wood a breeze. Small saws can be foldable which makes them safer to carry around.