Pruning Do's and Don'ts - Tree Pruning Guide


Pruning can be one of the most confusing aspects of landscaping. One of the best ways to kill your garden with love is to over-prune. But without pruning, how can you obtain that picture-perfect garden?

Tree pruning is simple in that the rules are fairly straightforward and apply across species; however, pruning a tree incorrectly is likely to cost you, in damage to your yard and possibly even the cost of replacing the tree.

Why to Prune

Main reasons to prune your trees include: pruning dead or dying branches, pruning damaged or diseased branches, and pruning branches that threaten your home or power lines. You should prune if the growth pattern of the tree will threaten its health, as is often the case when your tree grows a narrow crotch or crossing branches (Image A), or for aesthetics to keep your tree symmetrical and lush or cause it to produce more flowers.

Safety First

  • Don't prune a tree near power lines. Call an expert.
  • Don't use a chainsaw if the branch you are cutting requires the use of a ladder. Call an expert.
  • Do wear long sleeves and pants, safety glasses, and gloves (Sperian Safety Glasses, 212-2090; Garbotex Grain Leather Work Gloves, 660-1115).
Tools

One of the most important things you can do to make sure your trees are properly pruned is to use the appropriate tools. To prune tree branches, you will need:

Anvil hand pruners: for small branches up to 1/2 inch diameter. Test out the grip before you purchase to find something that's comfortable (Masterforce® Pruning Shears, 265-5955, 5956).

Long-handled loppers: for medium branches up to 2.5 inch diameter and long reaches. Loppers can become very tiresome, so choose a light-weight model (Yardworks Bypass Lopper with Control-Grip Handles, 265-5965).

Pruning saw: for large branches. A pole saw can also be used for higher, out-of-reach branches. (12' Pruning Saw, 265-6009).

Always keep your pruning tools clean and sharp. Sharp tools are important because they create a clean cut rather than tearing the tree fibers. This lessens the tree's stress and risk of disease or infestation. Clean tools prevent the spread of diseases. Especially when working on a tree you know to be diseased, dip your pruning tool in a solution of 1 part bleach to 9 parts water between every cut. Or you can use disinfecting wipes for a quick wipe-down.

When to Prune
  • Don't prune a tree the same year you plant it. The shock of switching soil will be enough for the tree to withstand for one year.
  • Don't prune an early-spring flowering tree (deciduous or evergreen) until the blooms are done for the year.
  • Do prune off any dead or diseased branches as soon as you see them, regardless of the type of tree or time of year.
There is no correct time to prune all trees. But there are some general rules you can follow to help ensure that you prune your tree at the correct time. Most trees should be trimmed in late winter or early spring to give the tree plenty of time to heal the wounds prior to the next winter. It is also easiest to prune for strength and health when there are no leaves blocking your view of the tree's structure. Light pruning can be done during the summer when the foliage is full; this will make it easier to thin the tree to the desired look and to identify and prune dead or diseased branches.

Flowering Trees

For flowering trees, do some research to find out if your tree flowers on "old wood" or on "new wood". Old wood means the wood that grew the previous year. New wood means growth that has occurred in the same growing season that the tree flowers. A tree that flowers on old wood will form buds in mid to late summer, then flower in early spring the following year. This means that any pruning you do between then will cut off the flower buds and you will have a year with no (or fewer) flowers. A tree that flowers on new wood forms buds in early spring and produces flowers shortly after, in late spring or early summer. This type of tree can be pruned anytime between when it stops flowering in the summer until before the tree leaves dormancy in early spring.

Whether you want to thin out or thicken up your tree's foliage will determine when is the best time to prune trees that flower on new wood. To promote new growth in the direction you want, prune trees right before they come out of dormancy in the spring. The fresh cuts will encourage new growth, jump-starting the corrective growing direction you want your tree to take. To thin out a tree, it is better to prune in mid-summer, once the sugars of the tree have begun to return to the trunk and roots to be stored for winter. This makes it less likely that new growth will be encouraged by the pruning.

Evergreens

The best time to prune an evergreen is in winter when the tree is resting or in late summer or early fall when new growth has stopped or slowed down. If the evergreen is a type that grows three or more shoots from a single bud, cut only the new growth (the candle) above the bud. If your evergreen grows from random buds throughout the tree (such as arborvitae, juniper, or yew), you can prune anywhere as long as you leave at least some of the foliage on each branch intact.

How to Prune
  • Don't prune more than 25% of a tree's branches each year.
  • Don't use patch or sealing products. When pruned correctly, trees have everything they need to seal themselves off and protect against bugs and diseases. Patches get in the way of the natural process.
Before you begin to prune, look at the overall shape of your tree and envision the shape you would like it to take. Determine which branches should remain intact and identify any branches that threaten the health of the "keeper" branches.

Pruning is really a simple process once you understand the science behind it. There are two types of buds, and they affect the way your tree grows. Terminal buds are buds at the end of each branch or shoot (Image A). They produce a hormone that inhibits the growth of any other buds along the same branch. Once the branch grows long enough, lateral buds (the buds along the sides of the branch) are no longer affected by the growth-inhibiting hormone (Image B). If you remove the terminal bud, the hormone production is stopped and the lateral buds are able to grow, producing a fuller, lush tree.

There are several types of cuts that can be done, depending on the results you hope to achieve. This means it's important to know your goal before you start hacking away. As discussed above, the timing of your pruning can result in thickening or thinning of your tree's foliage. The type of cut you make can also make a difference. To thin out a tree's foliage, you should remove entire branches, either back to one of the tree's main branches or to the trunk. Don't simply chop off a few twigs to temporarily make the tree look less dense, as this might have the opposite effect. To thicken a tree's foliage, use "heading" cuts, which means cutting a shoot back to a lateral bud that is already producing foliage, or remove just the terminal bud of the branch.

Branches that threaten the structure of your tree should be removed. Small branches can simply be cut off where they meet the larger branch, using pruners or loppers. Leave a small nub, about a half inch to one inch long, to prevent any damage to the larger branch (Image C). You should also look for water sprouts and suckers. Water sprouts grow vertically from other branches on the tree (Image D) and should be removed with pruners or loppers to prevent damage to the branch to which they are attached. Suckers are small trees that grow from the base of your tree (Image E), and must be removed because they take necessary nutrients away from the larger tree. Cut suckers off right down to the ground at a slight angle.

When removing larger branches using a pruning saw or pole saw, technique is important. First, about ten inches out from the trunk, cut up from underneath the branch, about one-third of the way through the branch. This cut will prevent the weight of the branch from ripping bark off of the tree. Then, an inch further away from the trunk, cut down until the branch snaps off cleanly (Image 1). You should have a branch stub about ten inches long remaining on the tree. Move in toward the trunk and remove the stub just outside the bark ridge and branch collar, sawing down and away from the tree (Image 2). Leave the exposed wood alone - the tree will heal itself within a few years (Image 3).