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.
It's common to think that everything should be chopped down to the ground in the fall, but some perennials actually need their foliage to protect new shoots through the winter. Other varieties offer up important habitat for local wildlife and some perennials provide height and interest through the winter months.
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.
Spent blooms should be cut back as soon as they begin to fade to keep reseeding issues to a minimum. But as you progress deeper into the autumn season, the foliage of daisies will begin to fade as well. At this point, it is time to cut the entire plant back near the ground for winter.
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.
Generally, the best time to prune or trim trees and shrubs is during the winter months. From November through March, most trees are dormant which makes it the ideal time for the following reasons: Trees are less susceptible to insects or disease.
After a few years in the garden, these perennials may start to produce smaller blooms, develop a 'bald spot' at the center of their crown, or require staking to prevent their stems from falling over. All of these are signs that it is time to divide.
By not cutting back the statuesque achilleas, eryngiums, perennial astilbes, sedums, alliums and many ornamental grasses, you can enjoy their structure against a winter sky. The sight of their stems silvered with frost adds a whole new level of interest to the garden.
Don't prune too late in northern regions.
In areas with cold winters, avoid pruning after the middle of August. If you prune too late, you may stimulate new growth that would not have time to grow thick, protective bark before the killing frosts of winter.
Plants are more brittle in cold temperatures. Messing around with them may cause branches to snap and split unintentionally. 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.
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.
In pruning, there are three primary types of pruning cuts, thinning cuts, reduction cuts, and heading cuts, each giving different results in growth and appearance.
Webb said pruning typically involves removing dead or diseased wood and thinning out stems and branches to improve the overall health and appearance of a plant. On the other hand, trimming typically involves cutting back plant material for reasons other than health concerns.
Don't shear the branches of spring flowering shrubs (Forsythia, Lilac, New Mexico Privet, Spirea, Flowering Quince, and others). These shrubs produce flowers on last year's wood, so removing old growth will reduce or prevent flowering. These plants should be pruned immediately after they are done blooming.
Most houseplants can be pruned and cut, however, there are certain kinds that care should be taken with— these include most palms and tree ferns. Dead fronds and leaves can be removed, but these plants never form branches, so the top areas of growth shouldn't be cut off, otherwise it will effectively kill the plant.
You should not do aggressive pruning in summer. Major structural pruning should wait until the plant is dormant in winter. Improper pruning will stress the plant. You might cut off valuable buds.
The best time to prune roses is in late winter or early spring, around the time new growth begins. This could be as early as January or as late as May, depending on your climate. If you'd like to mark your calendar, or set yourself a pruning reminder, here are regional estimates: Zones 3 and 4 - May.