Unfortunately, fall is not that time, as the plant is going into dormancy and not focused on producing new tissue, which protects the injury created by the cut. Late winter and early spring are the periods of most rapid growth for plants and is the most desirable time to prune.
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.
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.
Never shear a shrub in fall (or ever, actually, but that's another article) and leave major pruning or renovation for late winter/early spring, or immediately after bloom for spring-flowering shrubs.
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.
As a general rule, prune spring-blooming trees immediately after they flower. Prune trees that bloom in the summer or fall in late winter or early spring before the end of their dormancy. Routine pruning of dead or dying branches can be done at any time.
DON'T prune during fall.
No matter what type of shrub you have, fall pruning can stimulate late-season growth that may not have enough time to harden. This can weaken and damage the plant—especially if there's an early frost. Instead, wait until winter and trim bushes when the plant is in deep dormancy.
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.
Some perennials, like hostas, peonies and daylilies, need to be pruned in fall to avoid winter damage. Plants like these should be pruned after the first few frosts in late fall or early winter. Other perennials like mums and coneflowers are better off being pruned in spring just before new growth comes in.
The best time to prune is after flowering. If the plant needs to be renovated, or severely reduced, this can be done late winter and early spring just before growth begins.
Mild fall weather may have you thinking about pruning shrubs and trees. But it's better to wait till late winter, or, at least, after leaves have fallen. Fall isn't the right time to prune trees and shrubs. There are good reasons to wait till late winter or after the plants' leaves have fallen.
Prune evergreen shrubs, such as juniper and yew, in late March or early April before new growth begins. Light pruning may also be done in mid-summer. Avoid pruning evergreen shrubs in the fall. Fall-pruned evergreens are more susceptible to winter injury.
Because of the digging involved, you can also rule out winter, when the ground is frozen. Thus, the ideal time to remove large shrubs and bushes is when the ground isn't frozen and it isn't too hot outside.
Pruning to remove damaged, dead or diseased parts can be done at any time of the year. Most trees and shrubs, especially those that flower on current season's new growth should be pruned in late winter or early spring before the onset of new growth. (March-April).
Choose the Right Time
Likewise, prune in the early morning or late afternoon to avoid the newly cut ends of branches becoming scorched by the hot sun. Wait 48 hours after rain to prune, to allow plants to dry out and avoid fungal diseases. When pruning, make cuts just above leaf nodes, or buds.
In fact, it is better to prune a little at a time than to make drastic cuts. For plants that shed their leaves (deciduous plants), the best time for winter pruning is from the beginning of November to the end of February. To prune evergreens you can start later, from mid-December, and continue until February.
The best season to prune trees is while they are dormant, or generally between November and March. This means waiting for them to lose their foliage and cease growth, but before forming buds. For fruit trees such as the apple tree, prune in late winter.
The 1/3 rule involves cutting about 1/3 of wood during any pruning activity. This moderate pruning practice is a balanced approach to thinning out shrubs to stimulate new growth. The plant loses a good amount of stems, usually on the top section, allowing more light and air to enter the inside of the plant.
Leaves the crown open to wind damage and sun scald, and. Increases reaction, or stress-response, growth sprouts (“watersprouts”) along the trunk and branches. These reaction sprouts are a sign of over-pruning – the tree is putting out new growth quickly in an attempt to generate energy through photosynthesis.
Watering is very important during the couple of weeks or more that a plant is recovering from root pruning. Right after pruning, I give the whole pot a thorough soaking. As new growth begins, I make sure to thoroughly wet all the soil at each watering.
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.