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Trees & Shrubs: PRUNING

Rules for Pruning Ornamental Woody Plants

By Dana Dobias, Master Gardener

There are four things to consider when deciding to prune woody trees and shrubs. Consider what limbs or branches to prune, when is the best time to prune for a healthy plant, how to prune to allow for healthy recovery, and finally, should consider proper tool care.

When considering what limbs or branches to cut, the priority falls into three categories: 1) Dead, diseased or damaged; 2) branches growing in a way that could cause future problems; and 3) general shaping.

Dead, Diseased, or Damaged - Remove As Soon As Possbile

If the plant has a dead limb, it should be pruned as soon as possible. Dead limbs attract diseases and rotting organisms, which could spread further into the tree or shrub. If you are not sure whether or not it is dead, scratch the thin bark with a fingernail or a sharp tool. If there is green just under the bark, the limb is still alive and may be waiting for the proper time to sprout new leaves. Some woody trees have one or two growth spurts a year and cannot re-grow leaves as soon as a caterpillar eats all the leaves.

If the limb is diseased, it should be removed as soon as possible. Cut at least 6 to 12 inches below the affected area in case the infection has spread into the system of the plant. Clean the pruning tool with a 10% bleach solution, or 20% rubbing alcohol solution after every cut.

If the limb is damaged, especially common in northeast Oklahoma because of wind and ice storms, it does need to be removed at your earliest convenience, but wait until you are no longer upset about it. Making a rash pruning decision can be even more harmful to the tree. It may be worth the price of their consulting fee to be sure how to proceed.

Branches that could cause future problems:

Remove at the proper pruning time for each tree species.

Crossing or rubbing branches can cause bark to wear off leaving a place for diseases to enter. This needs to be pruned when the branches are young, or when it first occurs to prevent more extensive damage. Prune it at the proper time for pruning that specific tree or shrub (see below). If it is allowed to continue, the bark can become occluded, meaning the bark of the two different branches can grow together. Removing a branch after the bark has occluded can leave a large section of tree vulnerable to disease. Also, as the branches age and grow in diameter, the extra tissue builds up and creates a weak point. This weak point can cause much larger damage if it is torn apart in a wind or ice storm.

Branches that grow toward the center of the shrub should be removed at the proper time for pruning that shrub (see below). Center growing branches can cause a variety of problems, including shading too much of the center of the shrub causing an unusual shape, and a higher risk of crossing or rubbing other branches. Many of these branches tend to dominate the rest of the shrub and take over making it more of a tree shape. Each case is unique, but in most cases, it is best to remove the entire branch for center growing branches.

Water sprouts and suckers should be removed at the proper pruning time for each plant (see below). These grow straight up very rapidly. Water sprouts grow from branches. Suckers grow from roots. They often grow taller than the tree in a season. They have very few flowers or fruit, yet they take a lot of energy from the plant. If it is a root sucker from a grafted plant it may look very different from the original plant and can eventually overpower the plant to something udesirable.

If the sprouts are very young, you could try to rip them off (any time of the year). Ripping them off may remove the secondary buds near the base or branch collar of the sprout. Secondary buds will allow a second sucker to grow, repeating the problem.

Branches with a narrow crotch should be removed at the proper time for pruning the tree or shrub (see below). If the crotch angle is less than 45 degrees. The branches grow with a weak area and become susceptible to wind and ice. As the branches increase in girth each year, tissue builds up in the crotch area. This is a sign that the limbs are not growing in the proper and strongest pattern. The tissue is getting pushed out of the way. Eventually, a strong wind or a heavy load of ice will cause the weak area to break. Often this very large branch and makes for a much larger clean up than if a branch is pruned away before it is 1 inch in diameter.

General Shaping

General shaping is done at the proper time for pruning the plant (see below), and is not even necessary. Many homeowners choose to let trees and shrubs take their natural shape. If you decide to do additional shaping, there are many types to choose from.

Topping: the rounding of a tree crown. It is undesirable because it can produce many small, weak branches. It is more desirable to use thinning or heading methods of shaping. Thinning: removing selected, entire branches. It allows light and air to get to the center of the plant. Thus helping to reduce diseases and increase the health of the remaining foliage. Heading: a mid-branch cut. It makes thicker growth.

Trimming: removing just 6-8 inches of growth for shaping. This is done to each branch with pruners. If you choose to do this, please remember to angle the side so the lower branches are not shaded from the upper branches.

Shearing: shaping a single plant or an entire hedge. This is done with shears or electric clippers, and is generally considered inferior to heading or trimming. While this does give a very structured shape, a lot of the foliage is cut in half. If you choose to do this, please remember to angle the side so the lower branches are not shaded from the upper branches.

Coppicing / Cut-Down Plants: Cutting the entire plant to 3 to 6 inches tall. These are typically summer flowering shrubs that you can treat as a perennial. It helps keep them low growing and in many cases, the plants have superior flowering compared to just letting the plant grow naturally. These plants include: Autumn Sage, Beautyberry (Callicarpa), Bird of Paradise shrub, Blue Mist Shrub (Caryopteris), Butterfly Bush (Buddleia), Chaste tree (Vitex), Crape Myrtle, Corsican Hellebore, Elderberry, Firethorn, Glossy Abelia, Mimosa, Purple Smoke tree (Cotinus), Rose of Sharon, Russian Sage (Perovskia), Trumpet Creeper. Cut these down in mid March, fertilize and mulch in early April, then sit back and watch the fireworks!

Two additional rules about coppicing: 1) Do NOT coppice-prune a grafted plant and 2) single trunk trees can only be coppice-pruned when very young.

Fruit Trees, a link to an article entitled Pruning Fruit Trees and Small Fruits.

Pines and other needled evergreens - These have a unique growth pattern usually in spring. The new growth is at the tips of the branches and called candles. Prune these trees by pinching as much as one third to one half of the candles. This growth snaps off fairly easily when pinched between the thumb and forefinger. It gives the trees a fuller, more bushy shape and keeps them smaller longer.

Timing

The proper time to prune woody plants often depends on when it blooms. Cutting it at the wrong time can lead to not having flowers or berries. Weather can also damage plants if they are pruned at the wrong time.

Summer Flowering: i.e. crape myrtle, roses. These plants typically flower on this season's wood, so do not remove flowers or berries. It is usually okay to prune these in mid March. By then our chances of a really harsh freeze is very slim, but the plants haven't started new growth.

This is also the right time to coppice any cut-down plants you have. Spring Flowering: i.e. azaleas, forsythia, and hydrangea. These plants form their flowers during the summer and fall of the previous year. If they were pruned in the spring, flowers would also be removed. It is a leading reason why azaleas don't bloom. Prune these during the six weeks after they bloom. These plants usually burst out with new foliage during this time, so it is also good to fertilize them during the six weeks after they bloom. Use July 1 as a cut-off date for pruning these plants.

Bleeders: These include birch, elm, maple, and willow. They bleed a clear watery sap if pruned between Feb. 1 and the beginning of new spring growth. This sap does not harm the tree, but the constantly wet area may harbor diseases, especially one called slime flux

Fruit Trees, a link to an article entitled Pruning Fruit Trees and Small Fruits.

Wild hairs pop up here and there. If it is looking very odd, then it is perfectly fine to prune it off anytime of the year.

How to Prune

Study the tree or shrub carefully. Do not rush and realize later that you should have done it differently.

Decide whether all or part of the branch or limb should be removed. Leave a smooth cut, no jagged areas left to catch diseases. Leave the smallest cut possible. Less area for diseases to attack and easier for the bark to heal over.

Do not leave a stump or stub that will die and allow diseases to enter. Avoid cutting into the branch collar. This is the flared part of the branch where it attaches to the tree. Cutting into the collar often leaves a larger wound.

Do not leave an angle that collects water. This is another rule to help prevent diseases. Many disease organisms need water to survive long enough to establish themselves. Cut at 45 degree angle away from bud, if you are not removing the entire branch.

Tool Care

There are three times to inspect and care for your tools: Before - check to see that the tools are clean, and sharpen edges for best tool performance. During - clean the cutting blades with a 10% bleach solution or 20% rubbing alcohol solution. Either of these is adequate for sterilizing and preventing spread of diseases. The bleach is cheaper, but the alcohol does not cause corrosion of the metal.

Clean between every cut, if there is a disease. And clean everytime you switch to a new plant to prevent spread of a disease not suspected. After - do a final wipe of the blades, or wash them with a hose if there is a lot of dirt. Dry them and spray with WD40. Alternatively, many people keep a bucket of sand doused with oil in their tool area. Simply dip the tools into the oily sand and the friction of the sand cleans the tool, while the oil coats it and protects it.