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.
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.
Many gardeners cut back their perennials much too soon. There are nuances specific to certain perennials that dictate whether it is better to cut them back in fall or spring, but the general rule I like to follow is to only cut back perennials that start looking bad in fall.
Some perennials benefit largely from regular pruning during the summer growing season, but the most important cleanups are in the fall and the spring. A host of perennials respond best to a tidy spring cleaning and are seemingly rejuvenated from the practice.
The process of trimming back plants is the same for nearly all perennials. Begin by cutting the plant back to 3 to 5 inches above the soil line. Using a sharp pair of pruners or hedge trimmers, cut off all of the foliage and stems. Cut the plants down to within three to five inches of the soil line.
Pruning Perennials – General Pruning
In early spring, old foliage should be removed from most plants. Many spring blooming perennials should be pruned just after the blossoms fade. Perennial plants which bloom during summer and fall should be pruned in spring to create bushier, more floriferous plants.
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.
Daylilies are best cut back in autumn, once the leaves have had a full growing season on the plant. While there are some evergreen types of daylilies, most are herbaceous, meaning that the leaves die back in the wintertime and sprout anew in the early spring.
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.
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 keep their leaves through winter, like spring-blooming groundcovers, Heucheras, Hellebores, ferns. These are trickier. Spring groundcovers, like Candytuft and Basket of Gold should be sheared after blooming. Ferns and Heucheras should be cut back in late winter before new growth starts.
Frost zaps many perennials back to the ground. Plants are busy storing sugars and other nutrients in their roots to sustain them through winter. To support plants through this season of transition, make sure they get adequate water until the ground freezes.
2. Perennials and shrubs that are in your zone or one colder can be overwintered in an unheated garage, buried in the ground, or transplanted. 3. Perennials and shrubs in containers will need water through the winter but should not be kept wet.
By dividing the plant when it is not flowering, all the plant's energy can go to root and leaf growth. Fall division should take place between early September in the uppermost Piedmont and mid- to late October on the coast. Allow at least four to six weeks before the ground freezes for the plants to become established.
DON'T prune during fall.
This can weaken and damage the plant—especially if there's an early frost.
Always cut back to a leaf or part of the stem where you can see a new bud forming. Later in the season, when the plant begins to produce fewer blooms, you can just let them be. Let the plants stand during the winter to provide food for birds. In late winter, prune them back to the ground.
As a general rule, hostas should be cut back in the late fall. Start with leaves that have wilted or turned brown. Healthy leaves can stay a bit longer to help the roots store needed energy. If 25% or more of the hostas is dying, you will know it is time to cut it back.
It's during the early fall (September and early October in my Pennsylvania garden) when the night-time temperatures start to drop, that the carbohydrates begin to make their way back down to the plant crown. Wait to prune back hostas until the leaves turn completely yellow or fully brown.
The spent flowers quickly turn to a mushy bloom and then dry over undeveloped buds which can prevent them from opening. Removing the dead blooms keeps this from happening. Also, daylilies which have not been deadheaded will form seed pods.