Andrea is a garden writer and horticulture extension agent. She is a formally educated ornamental horticulturalist, but has a personal passion deeply rooted in edible gardening.

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MAKING THE CUT: Pruning Landscape Trees
by Andrea Dee    

Pruning is one of the best ways to give waning trees more vigor. Alternatively, it is one of the easiest ways to send a healthy tree into decline. Knowing how to make the right pruning cuts is a skill that takes practice and involves a lot of science too!  

When to Prune  
Flowering trees – Ornamental flowering trees that flower before June 1 should be pruned immediately after flowering to avoid shearing off next year’s flower buds. This includes redbud (Cercis spp.), Magnolia, dogwood (Cornus spp.), crabapple (Malus spp.), cherry and plum (Prunus spp.), peach (Prunus persica), pear (Pyrus spp.) and hawthorn (Crataegus spp.), which all set their buds for the following year shortly after flowering. Trees that flower after June 1 should be pruned similarly to shade trees, before new growth begins.

Shade trees – It is both easiest and most beneficial to prune shade trees while they are bare, before leafing out in early spring. Not only is their branch framework most apparent at this time of year, but the tree recovers better from pruning cuts made early in the season. Soon after the tree will start actively photosynthesizing providing necessary energy to seal pruning cuts naturally.

Evergreen trees – Evergreens are pruned in mid to late spring when the candles at the branch tips have formed. Simply pinch back branch-tip growth, called candles, to control size.  

Tools for the Job
Hand pruners with a bypass blade are recommended for branches ¼-½ inch in diameter. An easy rule of “thumb” is these branches will literally be no larger than your thumb! Loppers with a bypass blade are used for branches larger than ½ inch. And when that doesn’t make the cut, a hand-pruning saw or motorized chain saw is useful.  

Making the Cut
You have probably heard the old saying, “measure twice, cut once.” This same idea applies to pruning trees! It is always a good idea to step back and examine the tree canopy as a whole before making the first cut. While assessing the canopy think about the end result in shape, form, and texture. Concentrate on ways to remove whole branches back to the trunk to achieve the desired look and avoid stubbing branches.  

Start by pruning the tree from the top downward. This makes it easier to shape a tree. Most importantly remember to make each cut at the bark ridge of the branch. The bark ridge is where the branch meets the main stem or trunk. This ridge, also referred to as branch collar, houses special tissue that provokes the tree to compartmentalize the wounded wood. Compartmentalization is a tree’s way of “healing” the cut. If a flush cut is made removing the branch collar, the tree will not be able to set boundaries for resisting infection and decay. Alternatively, if a stub is left beyond the branch collar, the compartmentalizing callus tissue will not be signaled and the left behind stub will slowly rot. Most branches can be easily removed with pruners, however some may be larger and require a pruning saw or chainsaw. To ensure the safest cuts on larger branches an initial “stubbing” three-cut method is recommended.  

First, score the branch halfway with an upstroke approximately 12 inches from the main trunk. Second, make a full downward stroke an inch or so outside of the initial upward stroke. The length of the branch outside the cut should drop to the ground. Now that the branch is “stubbed” back, make a final downward stroke at the branch collar to encourage compartmentalization. This method of removing excess wood weight first prevents the tendency to peel the branch collar off, like when only one cut is made.  

Wound Dressing
Painting or packing tree wounds is not recommended. Microorganisms that promote wood decay populate easily behind paint and other wound dressings. Trees respond to pruning cuts through compartmentalization and are self-sealing in a way. Natural airflow and leaving the tree to its own defenses is the best remedy for preventing wood decay.  

Designing Perfectly Branched Trees
Special care is often taken in the way of careful planting and ample watering of young trees. Yet, sometimes encouraging a strong canopy with a pair of pruners is also necessary. When establishing a tree, corrective pruning can go a long way.  

Step back and examine the tree for a central leader. In trees like tulip poplar (Liriodendron tulipifera), black gum (Nyssa sylvatica), sweet gum (Liquidambar styraciflua) and pin oak (Quercus palustris) this will be a single, dominant leader branch coming to a point at the top of the canopy. In trees like maple (Acer spp.), ash (Fraxinus spp.), honeylocust (Gleditsia triacanthos) and dogwood (Cornus spp.) this will be a modified leader rounding the canopy at the top. If the tree is codominant, remove one branch to encourage a central leader to take effect. When a central leader is not established early enough, the bark becomes “included” at the bottom of the “V” crotch where the codominant branches meet. This area of the tree develops weak wood and the tree may split during storms.  

Remove whole branches rather than tipping back branches. Aim for a scaffold branch system, which encourages sunlight penetration and good air circulation. Establish well-spaced branches when the tree is about two years old. Prune young trees so that major branches are scaffold and 18-24 inches apart. Remove any water sprouts through the canopy or suckers at the base of the trunk. Water sprouts clutter the canopy restricting airflow and suckers steal water and sugar energy from the tree.  

Remove crossing branches since they damage the bark, opening sites for potential infection. Similarly, rough, broken branches should be removed with a clean cut to encourage compartmentalization.  

Say NO to Tree Topping!
Some homeowners are talked into believing that topping or dehorning a tree by “hedging” back all large and small branches to one even cut across the canopy is a healthy rejuvenating process for trees. This is false! Topped trees are unsightly and prone to quick decline. The shape of the tree is forever ruined and the immediate response of the tree is to force out heavy twig-like growth from the blunt stubbed branch ends. This is in an effort to replace lost canopy so the tree can continue to photosynthesize to provide for its established root system. These twig-like branches grow rapidly into weak wood that poses a hazard and easily breaks in storms. Instead of topping, take special care in selecting the right tree size for the right place!  

Pruning Safety and When to Use a Certified Arborist
Always use extreme care when pruning large branches. Green wood of most species weighs 30-60 pounds per cubic foot. Before you make a cut on a large branch, evaluate the fall and make sure you position yourself in a safe place. Wear protective gear such as gloves, helmet and eye protection. Never turn your back on a falling branch. If you are uneasy about pruning a tree yourself, consider contracting a certified arborist to do the job. The International Society of Aboriculture (ISA) certifies arborists to manage trees for optimal health safely. For a list of certified arborists in your area, visit, isa.org.

 

 

A version of this article appeared in a previous print edition of State-by-State Gardening.
Photography courtesy of Andrea Dee.

 

Posted: 02/06/19   RSS | Print

 

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