Pruning Ornamental Trees
Pruning methods for ornamental trees are somewhat similar to pruning both shrubs and full size trees, as they have some common characteristics to both.
Most trees, both small ornamentals and full size trees generally require less pruning than shrubs. Ornamental trees are generally grown for their desirable ornamental form. Over pruning can completely ruin or distort that form. The exceptions would be if you are pruning a shrub to a tree form or pruning a specific shape to a tree top or grafted tree (which would be a shrub in natural form, grafted to a tree trunk). In either case, more pruning is required to maintain an “unnatural” form. So don’t prune your trees because you think you should, most trees will not be as forgiving of mistakes as shrubs. You should have one of the following reasons for pruning:
- Remove all dead, diseased, broken and weak branches to insects and disease don’t enter the plant.
- Reduce the size of a tree that has outgrown its’ space and presents a safety concern, for example interfering with power lines. Or to remove lower branches interfering with people passing or mowing.
- Thin to increase air circulation to reduce insect and disease problems.
- Thin dense branches and foliage that prevent light from feeding the interior of a plant.
- Thin to expose interest growth patterns in the trunk and branches, or to expose interesting bark.
- Thin to reduce storm damage to dense trees (if strong winds can blow through the tree, rather than blow against dense foliage, the less likely you will lose branches, or the entire tree).
- Remove faded blooms and seed pods on plants that stop growth and flower bud production to produce seeds (see specific plant variety information). Additional flowering will be encouraged.
- Prune to encourage denser form.
- Shear or prune to form special shapes or topiary.
When to prune varies based on the tree, so be sure to see specific plant type information. Again, do not prune because you think you should, make sure you have a good reason to prune. These general guidelines are primarily for flowering and fruiting trees:
Trees that bloom early in the season, on last years growth, should be pruned immediately after flowering. Through the rest of the growing season the branches will grow and start flower bud production for next spring. The longer into summer you wait to prune, the more likely you will be to reduce flowering for next year.
- Trees that bloom later, on new growth and last year’s growth, should be pruned either right after blooming, or before the growing season begins (ideally after the first freeze in fall, and before the ground gets warm in spring).
- Trees that bloom in summer or fall, only on new growth, should be pruned in winter after the first freeze or in spring before the ground gets warm enough to start growth.
- Trees that produce ornamental fruits should be pruned after the fruit drops or before growth begins in early spring.
- Trees grown for fall and winter foliage color or colorful bark should be pruned early in spring before growth begins.
- Heavy pruning in late summer should be avoided in general. New growth will not be mature enough to survive in cold climates.
- Damage caused by storms should be pruned for repair as soon as possible no matter when it happens.
Depending on the types of trees you have to prune and trim, there are tools you will need. The most important thing when selecting tools is to choose tools that are most easily handled by you. For example, if a hand sized pruning shear is to large for you to easily handle, you will not be able to administer a clean cut, and will damage the branch. It is also important that your tools be sharp enough to make a clean cut without twisting and damaging the branch. These are the tools used for various pruning and trimming chores:
- Pruning shears for removing small to medium sized branches. A by-pass pruner (scissors style) will cut cleanly without crushing and damaging branches.
- Lopping shears, a pruner with long handles, will reach into the center of a tree and give you better leverage for cutting larger branches.
- Pruning saws are generally a long, curved, narrow saw compared to a standard carpenters saw, and has coarser teeth that are designed to cut on the pull stroke. The teeth are also designed to cut green wood without binding. A pruning saw is convenient for pruning trees or large shrubs.
- Hedge shears (large flat, scissors style shears) are designed to shear light new growth when shaping and maintaining foliage form. Ideal for light shaping and trimming of topiary and controlling form of a treetop.
- Pole pruners are for reaching tall branches. Pole pruners vary in their construction and use. Some are sturdy, some are somewhat flexible. Some have a rope pulley system to operate the saw, some do not. If you choose to do your own high pruning, which on an ornamental tree should not be too terribly high, investigate the operation of these pruners and try them out. Then get comfortable with the operation before beginning.
The biggest confusion for gardeners even when they know why they need to prune is how to go about it, and how seriously to prune. When it comes to pruning trees, generally the less pruning the better. Again, the exception would be when creating and maintaining an unnatural form of a small ornamental or shrub.
- The first step, and usually ONLY step in pruning a tree is to remove every dead, diseased, broken, damaged, weak and wayward branch. This will reduce the possibility of disease and insects entering the plant. Make sure your tools are sharp and clean. A pruner that has been in contact with disease will pass the disease to every plant you prune. Clean with a solution of 1 part alcohol, 9 parts water. And a dull blade will crush rather that cut the branches, leaving the branch damaged. Use your pruning shears, loppers, or pruning saw if the branches are large, to completely remove dead branches. Do not leave stubby branches, cut as close to the branch collar (the swelling where the branch joins the trunk) as possible without cutting the collar. This will promote quick healing. There is a chemical zone in the collar that inhibits the spread of decay, so you also do not need a tree wound dressing. If the branch is diseased, damaged or broken you can just cut back to healthy branch, which should not be black or discolored. If you have not removed back to healthy wood, the disease or decay will spread to the collar anyway, and the entire branch will later need to be removed. Make cuts just above an outward facing bud so that a new branch will grow out, rather than inward and crossing with other interior branches.
- The preferred method of pruning trees is thinning, which is removing selected branches back to a side branch or the main trunk. It opens up the interior of the tree to receive light, encouraging interior growth. Thinning can reduce the size of the tree and result in fuller growth. It also helps to maintain the natural form of the tree. Usually spacing of about 8 to 12 inches between the branches is best for good flowering and fruiting. Air circulation will also be improved by thinning, reducing insect and disease problems.
- Shearing should be reserved for topiary or maintaining an unnatural form of a small ornamental (often called clipping). Shearing is removal of the growing points (that is just the tips of the branches) at an even level using a hedge shears or electric hedge trimmer. The shrub responds by increasing the growing points. Each branch will generally divide to form a dense top layer of growth. The shearing method is used to form hedges or topiary. It has become common to “shear” for general shaping of shrubs and informal hedges. Repeated pruning by this method will cause foliage growth to be concentrated on the outside of the the shrub or ornamental, preventing light from entering the interior. Eventually the shrub or tree will become completely bare on the interior. Radical renewal pruning will be necessary. Thinning instead will maintain a healthy tree much longer.
There are a few things to keep in mind about the form of trees that will help you make pruning decisions:
- Ideally trees will have one central leader trunk with five to eight strong lateral branches from the main trunk, although the number can vary based on the size and natural form and density of the tree. The first major limbs should begin at least 5 feet from the ground and be spaced well around the trunk. Pruning limbs to make that happen should begin when a tree is very young. Once this framework is accomplished, only occasional maintenance will be necessary.
- Major limbs growing from the main trunk at less than a 45 degree angle will likely form a weak “V” crotch that may split during storms or with the weight of ice in winter. Good crotch formation resembles a “U”. Branches forming a weak crotch should be removed, allowing other lateral branches to become the major limbs.
- Many fruiting and flowering trees develop shoots or suckers from the base of the trunk and upright succulent shoots or watersprouts (these generally grow straight up and very quickly) along the main branches. These will starve nutrients from the tree and detract from the appearance of the tree. Remove these quickly while they are young, and treat the cut with a sprouting inhibitor. Delaying any pruning until midsummer may help the problem, but consider how that may affect fruiting and flowering of the tree.
- Topping a tree (cutting the top from a too tall tree at the leader trunk) will not only be unsightly, it ruins the natural form of the tree and makes the tree think you are trying to kill it. It will respond by sending up numerous suckers and watersprouts. The tree will often reach it’s original height in just two or three years, but this time with tangled messes of weak branches. If you must reduce the height or width of a tree, do it by thinning. Trace the offending branch to the trunk and remove the entire thing.
- Use the same method if a tree in front of a window has grown tall and dense, blocking the window from sunlight or views. Thin by removing entire branches to the trunk so that the tree is more open. Major limbs may also be removed from the bottom of the tree as mentioned above.
Many of the larger shrubs can be pruned to an ornamental tree, either single stemmed or multiple stemmed. Remove as many vertical stems as you wish, leaving one superior “leader” or several strong stems. Then, beginning at ground level, remove lateral branches completely to expose a trunk. Remove just a foot or two up from the ground, or much higher up if you prefer. Pruning a shrub to tree form may be started in a shrubs first year, but will also completely transform an old, full grown shrub.