How to Prune Trees & Shrubs
Pruning is necessary for many plants to get the best from them. There are many reasons to prune, and it is well to focus on why you are cutting away at your plant to get the results you want.
So, Why Prune?
To stimulate new growth.
To reduce or maintain size.
To remove dead, diseased, or broken branches
To encourage flower and fruit development
To rejuvenate old, overgrown plants
To reduce danger of injury and/or damage to property
To improve light and air circulation
What happens when we prune?
Some understanding of plant biology will make it easier to decide what, when, and how to prune. Every branch or stem has a terminal bud at the tip. This bud produces a hormone (Auxin) which suppresses the growth of the buds appearing along the stem. Cut off the tip and the side buds start to grow. This occurs most strongly in the 6 to 8 inches of the branch closest to the tip. Cutting off the tip when the plant is dormant in winter will stimulate more side buds to grow in the spring. Tipping in summer will only stimulate one or two buds below the cut.
Cutting a branch causes a wound which the plant immediately tries to heal. The hormones that help heal wounds are most highly concentrated at the buds, and where each branch joins a larger branch or the trunk. Cutting a branch away from the bud or the joint makes it harder for the hormone to reach the wound. Two areas on the plant - the bark ridge at the junction of two limbs and the branch collar where the branch joins the main limb will eventually close off the wound caused by the pruning cut. For fastest healing, prune as close as possible to the ridge or collar without injuring them.
Types of Pruning
Pruning falls into two major categories – heading and thinning. Heading basically cuts of the ends of branches. Examples include shaping shrubs for a neater appearance, shearing plants into a hedge, or pollarding, which cuts back a plant to a few main branches.
Heading, as you remember from our little biology lesson, will stimulate lateral branching, causing the plant to become thicker. Thinning involves cutting branches back to a larger branch or to the base of the plant. Thinning cuts can reduce the size of the plant, give it a more pleasing shape, and allow better air circulation without changing the basic natural shape of the plant.
When to Prune
Most plants can be pruned to cut out diseased damaged or dead branches at any time of the year. Otherwise, when to prune depends on why you are pruning. If you are working on the basic shape of a deciduous plant, winter is the best time. The plant is dormant, and you can see what you are doing. Broad leafed evergreens pruned while dormant will put out more new growth from lateral buds in the spring. Conifers, however mostly only put out new growth at the tips of branches. If pruned back to older sections of branches without leaves they mostly will not regrow.
If you are controlling the size of the plant, remember winter pruning will stimulate more lateral branching. Spring and summer pruning will only stimulate one or two lateral branches.
Finally, when pruning any flowering plant, you want to know whether it blooms on new growth, or on older wood. If it flowers on new growth, cut it back in winter to stimulate new shoots and get rid of old ones. If it flowers on last seasons growth, wait till it finishes flowering and then prune if you need to.
Rejuvenating Old Plants
Whatever the plant, you should avoid pruning it in the fall. The new growth stimulated by your clipping will be frozen by the first frost before it has a chance to toughen up.
Sometimes things get away from us or sometimes we inherit someone else’s problem. For whatever reason, we are faced with an overgrown monster that is swallowing our house, walk way or yard. What to do? Well it depends on the monster.
Overgrown conifers such as junipers, arborvitaes, cypress, and such are difficult to remediate because thy generally do not regenerate when you cut into older wood. You may remove the lower limbs to make a tree form. You can take the top out, but it can take years for new growth to disguise the damage. Many times, the best solution is to remove them.
Broad leafed plants are easier to fix by either by either of your two basic pruning methods: shearing thinning. Some stalwart shrubs such as hollies, ligustrums, wax myrtles, nandinas and the like can simply be pruned back close to the ground and allowed to regrow. Other shrubs can be tackled by thinning over the period of three years. Choose the oldest, gnarliest, ugliest stems and cut them to the ground. Take no more than a third of the plant Next year take out another third, and the third year remove the remaining old branches, leaving an entirely rejuvenated plant.
Pruning really isn’t rocket science, and observing a few basic rules will allow you to keep your yard in control. And take heart. Most plants are very forging and even terrible mistakes will disappear in time.