It is done to remove diseased or dead wood, to eliminate crossing branches, to make some evergreens bushier and to shape unruly trees. If done well, it enhances the appearance and health of the tree; if done badly, it can introduce infections and shorten the tree's life. It isn't, however, difficult to learn how to prune well.
Every branch needs a place to be. It is the reason for pruning otherwise healthy trees. If a branch is close to or already touching or crossing another, it will get worse as they grow. Removing or shortening one or both will create needed space. It also allows air circulation and sunlight, both necessary for leaf growth, to enter the inside of the tree. Dead branches are a potential place for disease to grow and are best removed. Already diseased branches must be removed if the problem is not to spread to the rest of the tree and possibly neighbouring ones, as diseases can spread by insects and wind.
Trees are so often planted in the wrong places, with little or no thought to mature size, that the answer seems to be to prune it to keep it small. This is a short-term, frustrating solution that ultimately doesn't work. Trees are genetically programmed to reach a certain adult size. Removing a large proportion of the branches means that the tree has fewer places to put needles or leaves that are necessary for photosynthesis. The roots absorb water and nutrients from the soil, but there aren't enough leaves or needles to absorb sunlight, which the plant needs for survival. Often, it is better to replace a tree that is outgrowing its space and replace it with a more appropriate tree.
Spruce trees are a perfect example of this. Those cute little trees that look so perfect in a flower bed will grow to twelve feet wide and thirty-five feet high! The needles on the inside of the tree die every fall. This is a natural occurrence and not an indication of poor health. Each spring, new needles grow on the tips of the branches. If these are removed, as the oldest needles die, the tree will resemble a telephone pole with green needles only on the ends. If a branch doesn't have enough needles, it will begin to die.
There are a few easy rules for pruning. A branch to be removed completely, or back to a much larger branch, is cut at the outside of the collar, a wrinkled area where it joins the trunk. A branch that is to be shortened is cut just beyond a smaller branch, which will be at the end, and at the angle of that branch. A few years after purchasing a young tree, it is a good idea to evaluate the tree's structure and create a 'backbone' for future growth. Look at the tree from several directions, before it leafs out in the spring, and prune to allow each branch future branch space, and shorten to practical size and natural shape of that tree. A tree should never look 'pruned' after you are finished, simply tidier and nicely shaped. If this is repeated periodically, the tree will rarely need drastic pruning.
Most deciduous trees and shrubs are pruned in the spring before they leaf out. Exceptions are birch and maple, which are pruned in July after rapid spring growth finishes. They will drip copious amounts of sap if pruned in the spring - remember where maple syrup comes from? Birches do the same thing, and syrup can be made from them, too. Shrubs that flower in the spring on buds that are formed in the fall, such as Nanking cherry, lilac, some roses, and white flowering spireas, are pruned after they bloom. Shrubs that flower in the summer, such as pink flowering spireas, most shrub roses, and potentilla, are pruned when green buds appear. Any winter tip kill is removed and branches trimmed to an appropriate size and shape. Pine trees and shrubs have new growth called candles that are snapped in half in June to make a somewhat bushier appearance and compact shape. Spruce trees are rarely pruned, although many people remove a few of the lower branches when most of the needles have died. Junipers and cedars may be sheared a little, but remember the rule about removing too many new needles!
Pruning shears are used for small cuts and should be sharpened frequently enough to make clean cuts. Somewhat larger branches may be removed with lopping shears, or a saw. If a large branch is to be removed completely, make an upwards cut a foot or so beyond the trunk, halfway through the branch.
Then cut downwards beyond that cut. The branch will break off when it is being cut downwards, and default to the upwards cut, but not damage the trunk. The final cut can be made without ripping bark off the tree as it falls.
Keep pruning tools clean and sharp. If the tree is diseased, clean after every cut by dipping into a solution of one part bleach to ten parts water. Don't try to prune beyond your capabilities! If you are not sure you can handle it, call a certified arborist, who has the proper knowledge, experience and tools, to do the job. Pruning is quite satisfying and interesting. Creating a shape for a tree that is pleasing and natural can be a work of art.
The basic objectives of pruning are to maintain the plant's natural shape, to maintain its health and vigour, and to keep it a manageable size. Several general rules need following no matter what type of pruning you are doing. Know when to prune your plant material and determine the type of pruning needed. Pruning cuts should be made with a sharp and clean pruning tool such as pruning shears. Disease organisms can be spread from branch to branch or from tree to tree if your pruning tools are not kept clean. Clean your pruning tools by dipping them in bleach (1 part bleach & 10 parts water) or alcohol between cuts, on disease-infected plants or between plants, on disease-free plants. So as not to leave any stubs that will inevitably die, pruning cuts should be made cleanly and on the outside of the collar (wrinkled area between trunk and branch). Pruning cuts on small stems are always made just above a leaf or branch joint or node. Large pruning wounds can be painted with pruning paint to prevent the entry of disease organisms. Damaged, dead or diseased wood should be removed as soon as it is noticed. Branches that are crossing should be removed before they enlarge and start rubbing together. Try to maintain the natural shape of the tree or shrub. Carefully select which branches should be removed or headed back so as not to spoil the shape of the plant.
Try removing branches that have grown too close together as well. Prune the branches in the right place by selecting a bud pointing in the direction you want the branch to grow. Prune about a ¼ inch above the bud at a 45-degree angle. This leaves less stub and is less likely to be diseased.
1. Just right.
2. Pruning angle too Steep.
3. Pruned to short.
4. Pruned to long.
Also, it is important to angle your cut so that sap weeps away from the bud for the same reason as seen in Figure one.
Figure two shows the wrong angle and too steep a cut.
Figure three is cut too close to the bud. Figure four is too far away from the bud and will leave a long length of deadwood.
Newly planted hedges such as Cotoneaster, Caragana, Lilac, and Cranberry; should be pruned back to encourage lateral branching which creates a fuller hedge more rapidly. As your hedge develops trim it so that the base is wider than the top. This allows sufficient sunlight to reach all leaf surfaces, preventing the base of the hedge from becoming open and sparse. Hedge shearing can be carried out at any time during the growing season. Older hedges in need of rejuvenation are more easily thinned out during the dormant season, in the early spring before new growth appears or in the fall after the leaves have fallen.
Pruning Shrubs That Flower on Old Wood
Shrubs that flower on old wood in the spring such as Forsythia, Double Flowering Plum, Nanking Cherry, or Lilac, for example, should be pruned as soon as flowering is finished. Pruning at any other time of the year will remove the dormant flower buds. Flower buds for most shrubs are formed on the previous year's growth. White Spireas such as Bridal Wreath, Garland, and Three-Lobed also flower on old wood. Any other shrub that flowers in the summer on old wood should be pruned immediately after flowering. To prune older shrubs, usually requiring thinning, occasionally remove entire large branches by cutting them out at the base.
Pruning Shrubs Shrubs That Flower On New Wood
Shrubs that bloom on new wood, such as Elders, Hydrangea, Dwarf Pink Spireas (S. bumalda and japonica cultivars), Group C Clematis jackmannii, and most roses including Hybrid Teas and Parkland Series; may be sheared to close to ground level in the spring to remove old wood. Flower buds are formed on the current year's growth. All other shrubs not listed above bloom on old wood. Suckers that emerge from below ground are removed during the summer, as they originate from the rootstock, not the plant grafted onto it.
Pruning Shade Trees
Shade trees should be trained when they are still young. By shaping shade trees early, unwanted lower branches, crossing or rubbing branches, and branches growing in the wrong location or direction are eliminated. Most shade or ornamental trees prefer to be pruned during the dormant season, in early spring. Birch and Maple (which are called "bleeders") are exceptions, however. These species should be pruned in mid-summer, usually in July or August. Pruning cuts on Birch and Maple do not heal quickly because they bleed sap if pruned before their leaves are fully expanded. Most shade trees, if properly located and pruned when young, may require less pruning when mature. If you do have large trees requiring pruning, we recommend you consult a professional pruning service.
Pruning Fruit Trees
Fruit trees such as Apple, Plum, or Pear, are pruned during the dormant season in early spring to encourage vigorous growth and to create a better-producing tree. Prune fruit trees so that all parts of the tree receive adequate sunlight. Unwanted lower branches, crossing or rubbing branches, and branches growing in the wrong direction or location should be removed when the tree is young. Any suckers growing from the roots or water sprouts growing from the trunk should also be removed. To prevent fruit from overloading and breaking permanent branches the smaller, outside branches should be also be thinned.
The new growth on pines, called "candles", should be cut in half in June, after the new growth has hardened, to encourage a compact shape. Cedars and junipers may be shaped at any time. The long soft, new growth on spruce may be shortened to shape it or minimize growth, in June. If the leader of spruce is damaged or removed, a new one may be formed by tying a sturdy stick to the trunk, extending it above the top of the tree, and bending and tying one top branch up to the stick. You can avoid having to keep evergreens smaller than their natural size by choosing varieties that have an appropriate mature size.
A canker is defined as a diseased, sunken lesion on woody tissue. There are three types of cankers; fungal, bacteria or frost.
Frost cankers, actually physiological disorders, are cracks on the bark caused by freezing and thawing. Fungal and bacterial pathogens usually gain entry through frost cracks, pruning wounds, wind damage, or sun-scald. Sunscald is another physiological condition that occurs on the southwest side of tree trunks exposed to bright winter sunlight, most often affecting May Day trees. Fungi are microscopic plants that do not invade healthy plant tissue. Once inside the plant the fungi move into the sap system and eventually decrease or stop water from moving upward from the roots to the branches. If you look closely at the trunk where the branch is attached, you may see cracks in the bark with the bark peeled back from the crack; elongated oval, sunken or darkened areas in the bark or places where sap is oozing from broken areas in the bark.
One common fungus causes Cytospora canker in Cotoneasters, particularly inside older hedges where there is little light or air circulation; a perfect place for fungi to grow. The commonly observed orange Nectria canker on Cotoneaster is a secondary rot organism that does not harm the plants themselves. Some of these cankers are incorrectly diagnosed as fireblight, in which the leaves die because the bacteria kill them, and then the cankers come afterwards.
While possible on most trees, fungal Cytospora cankers are most prevalent on Mountain-Ash, Poplar, Spruce, and Willow. Bacterial cankers, also called Slime Flux or Wetwood, are most frequently observed on Poplar trees. There is no chemical control for fungal or bacterial cankers. The only way to control them is to prune the branches back well into healthy wood. In the case of hedges; remove the inside, affected branches and then the remaining branches will grow into the center because of the available light and air circulation. This is not a cure as the fungi or bacteria could spread within the sap of the plant and cause more cankers. Eventually, if it invades the main trunk, the tree may have to be removed.
Be careful to clean pruning tools with a 10% bleach solution between each cut, as fungi or bacteria spread on tools. It is difficult to diagnose cankers by describing them on the phone so bring in a branch to our staff for easier identification.
The use of proper pruning equipment, to complete the job at hand is very important. It will not only save you time but also money. One problem that we see at the garden centre is that people bringing in broken pruning equipment want to know why it happened. Often it happens because we try to save time by doing the job with one tool. Small hand pruners should only be used to cut branches the thickness of your little finger maximum. The next tool up would be the lopper. The longer the handle the more leverage you will get, but cuts larger than 1 inch (2.5 cm) should not be made. This size of cut can also be made with a long-handled pole pruner, but the more the pole is extended the harder it is to prune. Leverage is a funny thing. Whenever possible use a ladder with the pole pruner, this will enable you to get higher up into the tree without extending the handle all the way. When the cut is larger than one inch in diameter, a saw should be used. For very large branches, a chainsaw would be the tool of choice but must be used with extreme caution, and proper safety equipment.
Both the small one-handed pruner and the lopper come in two different styles. The first is the anvil pruner, where the blade comes down onto a chopping block. (anvil.jpg) We, however, do not recommend this type of pruner, because it tends to crush the branch and tear the cambium layer, which slows the healing process, and can cause health problems later on, such as rotting as well as insect and fungus entry. These anvil type pruners are great when removing a tree completely because it allows you to use more pressure without causing more damage to the pruner. These now often come in ratchet style for this purpose. Ratcheting makes it possible to take down thicker branches with ease. The second type and most practical is the hooked or curved blade. It is frequently called a by-pass pruner, (bypass.jpg) where the blade passes by the cutting block, similar to a pair of scissors. This allows a nice clean cut to occur, which helps the healing process. There are many styles available so it is important to find one that is comfortable and practical for the amount and type of use. (lopper.jpg) Some larger bypass pruners will make short work of heavy branches. They are designed for this purpose strictly and sometimes smaller branches get caught in the pruner and are torn not cut. Take a good look at what you need to prune before you buy. Bigger does not always mean better.
If pruning hedges there are manual, gas, and electric hedge shears available. For small jobs, manual hedge shears work great and are much easier to sharpen. For larger jobs, electric or gas shears will save you time. Gas shears are much more powerful and versatile, however are not as easy to service or sharpen. One thing to keep in mind when pruning a hedge is that the bottom of the hedge should be kept wider than the top of the hedge, as this enables sunlight to reach all the leaves and to prevent die-back and thinning from lack of light and air circulation.
Check out some of our pruning tools
available in store on our Pruning Tool Catalogue page