Although it may be cold and snowy outside, winter is actually the best time of year to prune your deciduous plants. Wait for a relatively mild, sunny day, get out your pruners, and take a critical look at your trees and shrubs.
An improper cut like a flush cut (cutting too close to the trunk) or a stub cut (cutting too far from the trunk) can cause irreversible damage to a tree. A flush cut removes the branch collar and leaves a large wound in the side of the tree that won't heal properly.
No Flush Cuts
While it may look clean and streamlined, a flush cut removes the branch collar, an area of tissue that's needed to form a seal over the pruning cut. Because the plant cannot close over the wound, a flush cut leaves an opening for pests and pathogens to enter the plant and damage or kill it.
Municipalities and homeowners often remove the lower limbs for pedestrian and vehicular clearance or to let the sun shine in for grass to grow. Mature trees, especially evergreens, benefit when healthy lower branches are left intact. Removing large limbs can increase the risk of decay.
After “how?", the second most-asked question we get about pruning is “when?” (Or, "Can I prune this now?") The rule of thumb is to prune immediately after bloom for flowering shrubs, in late winter or early spring for non-blooming shrubs (particularly for heavy pruning), and not after mid-August for any shrubs.
Summer-Blooming Trees and Shrubs
Prune them in winter while they're dormant, or in early spring just before they push out their new growth. You can even cut them all the way to the ground in late winter, and they'll still bloom that same summer.
During excessively cold temperatures
It's minor, but it could impact the look of a plant or create a haven for insects and diseases later. Don't prune when the temperature falls below 25°F.
Pruning can make plants hardier and help them over the winter too. Other plants, however, can't handle fall pruning—such as azalea, viburnum, Loropetalum, and lilac. If you prune a spring-blooming tree or shrub after its flower buds have formed, you'll be lopping away any opportunity for a spring showing.
It's important to cut back foliage in the fall to protect flowering plants from disease and give them a clean start for regrowth as winter starts to turn into spring. However, there are some plants you can keep around through the winter since they benefit wildlife and still offer visual interest for your home.
Also, do not cut back hardy perennials like garden mums (Chrysanthemum spp.), anise hyssop (Agastache foeniculum), red-hot poker (Kniphofia uvaria), and Montauk daisy (Nipponanthemum nipponicum). Leave the foliage. It's important to protect the root crowns over winter.
But when should hostas be cut back? Hostas should be cut back in late fall. Healthy hosta leaves can be left on the plant in early fall to capture much-needed energy, but all leaves should be trimmed off after the first frost to deter slugs and other pests from making your hosta their winter home.
DON'T prune during fall.
This can weaken and damage the plant—especially if there's an early frost.
Any gardening expert will tell you, (contrary to what you may believe) that pruning encourages new growth just when the plant is trying to go dormant and new growth doesn't have enough time to harden before the first frost and freezing temperatures hit. Pruning at this time of year will severely weaken the plants.
You probably already know just how fast shrubs grow and start to look messy. If you wait too long, your shrubs will start to become an eyesore. Pruning less of the plant but more frequently is by far the best for the overall health of it. We recommend every other month, which comes out to be five times per year.
Common Mistakes
Prune just above a healthy bud, with the bud pointing in the direction you want the plant to grow. Cut at a 45-degree angle, with the low point of the cut opposite the bud. Don't cut too far from or too close to the bud you want to encourage. Leave a “collar” when cutting off a branch.
Late summer or early fall pruning causes vigorous re-growth of tissue, which in some cases may not harden off by the time winter arrives, leading to possible cold damage to the new growth.
Overgrown trees can pose a serious risk to your property and your family. Dead or damaged branches can fall and cause damage to your home or car or even injure someone. In addition, overgrown trees can block sunlight and views and can even damage foundations or driveways.
Pruning during the growing season always stimulates new growth. During summer's heat, having to produce that ill-timed new flush of growth greatly stresses a tree. Pruning in the fall is even worse as it prevents the tree from going into a natural dormancy. The exception is heavily damaged, disease or dead wood.
You should only remove 10 to 20 percent of the tree branches from the edge of the canopy. Large trees benefit from removing end portions of limbs between 1 to 4 inches in diameter. Small ornamental landscape trees and fruit trees can be thinned by removing smaller limbs between ¼ to ½ inch thick.
If a tree repeatedly loses too much of its canopy at one time, it can become weak or even die from the stress. That's why you shouldn't trim more than 25% of a tree's canopy at one time. Cutting the branch collar can also be a nasty error.