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Snow damage pruning

Getting shrubs on the road to recovery from winter snows

By: Sandy Feather ©2010
Penn State Extension


Q. The big northeastern US snowstorm in early February 5 caused extensive damage to plants in my landscape. Big limbs were broken out of a mature white pine, my red twig dogwood is absolutely smashed, and the blue hollies do not look much better. Can you tell me how to prune out the damage properly and get them on the road to recovery?

A. It is hard to recommend specific pruning cuts without seeing the damaged plants in person, but I can make some general recommendations. First off, it is critical that you hire a certified arborist to deal with large trees that have sustained storm damage, such as your white pine. They have the training and equipment to properly and safely prune large trees, and to assess the future stability of damaged trees. Undoubtedly some trees that have major structural damage will have to be removed for safety’s sake.


Major Losses from Heavy Snow

It is hard to lose mature trees since it takes so long to replace the shade, shelter and character they bring to the landscape.

Broken branch on a large Pin Oak

Although many fast-growing large trees have a well-deserved reputation for being weak-wooded, there are some that grow reasonably fast without that liability. Some replacement trees to consider include Freeman maples (Acer x freemanii), silver linden (Tilia tomentosa, especially Green Mountain®), dawn redwood (Metasequoia glyptostroboides), disease-resistant American elms such as ‘Valley Forge,’ (Ulmus americana ‘Valley Forge’) and Japanese zelkova (Zelkova serrata).

 


Smaller Tree Damages

Home gardeners can safely prune broken branches from small trees and shrubs. In most areas, enough snow and ice has melted away so that you can clearly see the problem areas. Cleaning up storm damage is mainly a matter of removing damaged branches and cleaning up the ragged edges created when they snapped. A clean, well-placed pruning cut will heal more quickly than a jagged tear and help restore trees and shrubs to health and good form. As with large storm damaged trees, it may be that some small trees and shrubs have been damaged so severely that they will have to be replaced. Much depends on the growth habit and vigor of the damaged plant, as well as the severity of the damage.
  

Arborvitaes damaged by heavy snow

There are some basic pruning principles you should know before you grab the pruning saw and limb loppers. This is going to be the Reader’s Digest Condensed version since space does not allow me to go into great detail. I encourage readers to reference this website, as well as the websites listed at the end of the article, for a more in-depth explanation as well as drawings of various pruning techniques and equipment.


Making the Right Pruning Cut

Especially when pruning small trees, if you must remove a limb back to its point of origin on the trunk, it is important to preserve the branch collar. This is a noticeable swelling where the branch joins the trunk. Make your pruning cut to the outside of the branch collar rather than making the cut flush with the trunk. The trick is not to leave a large stub while not cutting into the branch collar.

If the limb is over 2 inches in diameter, be sure to use the three-cut method to remove the branch to prevent tearing the bark down the trunk of the tree when the limb falls. Make the first cut up from the BOTTOM of the limb, 10 to 12 inches out from the trunk. Make the second cut three or four inches out from the first cut, down through the limb. As the limb starts to fall, the bark stops tearing at the initial under cut. The third cut removes the remaining stub while keeping the branch bark collar intact.
  

How to leave the branch collar when pruning a tree

Do not use pruning paint or sealer of any kind. Trees and shrubs are capable of healing over good pruning cuts, and those products can interfere with that process.


Tree Bark Repair

If the storm damage has already torn the bark down the side of a small tree, try to clean up the ragged edges of the bark with a sharp knife. Ideally, you want to excise the damaged bark in an elliptical (think football!) shape around the wound, but trim as close to the wound as possible to avoid damaging more bark.

Finally, you may not have to remove a broken branch entirely if you can remove the damaged portion back to an outward facing side branch. Always try to prune to side branches or buds that are growing or pointing out from the tree to avoid having the branch grow back into the center. This avoids having branches rub against each other and keep the center of the tree open to air circulation and sunshine.


Snow-damaged Shrubs

Suckering shrubs are the easiest to rejuvenate from this kind of snow and ice damage. These shrubs generally have several to many stems coming out of the ground. When you prune them – especially if you prune them hard – they often respond by sending more stems (suckers) up out of the ground. Vigorous plants with a suckering growth habit can be taken to within several inches of the ground and allowed to re-grow, which should remove any winter damage.

 

Although you will sacrifice this year’s blooms of those shrubs that bloom on last year’s growth (“bloom on old wood”), it is worth it to recover a strong, attractive framework of stems or branches. This is best done sometime in March so the plant only has to produce a single flush of growth. Pruning after the normal spring flush of growth requires the plant to produce a second flush of growth, depleting the shrubs’ carbohydrate reserves. Suckering shrubs include bottlebrush buckeye (Aesculus parviflora), summersweet (Clethra alnifolia), red twig dogwood (Cornus spp.), forsythia (Forsythia spp.), northern bayberry (Myrica pensylvanica), elderberry (Sambucus spp.), (Syringa spp.) and many others.

Other shrubs, such as your blue hollies, grow more like small trees and you should follow the instructions above for pruning them.
 

Blue holly hedge

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