Pruning 101

Now that the leaves have fallen, it is time to pick up your pruning shears, loppers and pruning saws.  The best time to prune trees and shrubs is when they are dormant.  You can easily see branches to determine which to prune and plants have stored food in their roots, stems and branches so they will not re-sprout from pruning cuts now.  Prune trees when they are young for several years to establish an appropriate shape and you won’t need to continue pruning as they age. Pruning is truly and art and a science.  Prune to shape trees and shrubs to grow in their natural habit, but also prune properly to avoid spreading decay throughout the plant.

There are two important pieces of information to remember about the way trees grow.  First, branch tissue and trunk tissue are separate.  Second, trees never heal, but then can compartmentalize and seal wounds.  They seal wounds by growing callus tissue around the cut.  Decay spreads most easily vertically in a tree, so it is critical to cut only branch tissue and not allow decay to enter the trunk. When cutting a branch, always prune outside the branch collar (swollen area at the base of a branch).  Never cut flush with the trunk as you will be cutting into trunk tissue and opening the tree for spreading decay.   Forget about using a wound dressing, they only inhibit the tree’s natural callus response to a pruned branch.

Start by pruning any dead, dying or diseased branches.  These branches can be pruned at any time of year.  Next, look for rubbing or crossing branches.  Rubbing branches may create a wound that will be open for insect and fungal entry.  Crossing branches can eventually become rubbing branches as they grow.  Remove branches that are growing back into the center of the tree and keep branches growing outward.  Finally, remove water sprouts and root suckers.

Use the appropriate tool for the job.  Pruning shears are handy but shouldn’t be used on branches larger than ½ inch in diameter.  Lopping shears give you more leverage and can prune slightly larger branches.  For branches greater than ¾ – 1 inch, switch to a pruning saw. Pole pruners can be used to prune branches that are too high to reach but be careful of overhead wires when using pole pruners.

If branches are large, use three pruning cuts to prevent the weight of the branch from peeling back bark and allowing the wound to enter trunk tissue.  Start by undercutting the branch about 4-5 inches away from the trunk.  Then saw through the entire branch outside that undercut, removing most of the weight of the branch.  Make your final cut just outside the branch collar.

Hedge clippers should only be used for pruning shrubs maintained as a formal hedge.  Always prune the top narrower than the base to light reaches all the branches of the hedge.  There is no shrub that should be pruned into a ball, despite what you see in the landscape around you!  Prune individual shrub branches just above a node or bud to reduce the size and maintain natural shape.

Some shrubs respond well to rejuvenation pruning.  Redtwig dogwood, for example, can be cut back to 4-6 inches above the ground and allowed to regrow new branches that will be vigorous and more brightly colored.  When you want to encourage new growth, prune late in the winter just before growth starts.  If your goal is to reduce plant size, prune in the summer when most of the plant’s resources are depleted.  For blooming shrubs, prune after the shrub flowers.  Some shrubs bloom on new wood and will respond well to a dramatic pruning.  Other shrubs bloom on old wood and removing too many branches will dramatically reduce flowering.

Red twig dogwood responds well to rejuvenation pruning and will grow bright red new twigs for the following winter.

For more information about horticulture in Delaware follow me on Instagram at sbartonhort.

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