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.
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.
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.
With thought out pruning, perennials can be timed to bloom in continuous waves. Spring blooming perennials should not be pruned until after flowering. Summer bloomers should be pinched in early spring. Perennials that bloom in the fall should be cut back by July 4.
Cutting back perennials in the fall is not only a great way to keep flowerbeds looking neat and tidy through winter, but it also aids greatly in keeping plants vibrant and blooming the following year. Removing spent foliage and blooms helps a plant focus on recharging it's roots and resources.
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.
Prune foliage down to just a few inches from the ground and make sure to clear away any debris from the garden to help prevent disease and rot in the early spring. If perennials (like Bee Balm or Phlox) were diseased this past season, cut the foliage all the way down to the ground and don't compost it.
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.
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.
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.
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.
If your perennial blooms in the spring or early summer, it should be transplanted in the fall. If your perennial blooms in the late summer or early fall, transplant it in the spring. Remember that when transplanting in the fall, the perennial needs to be in its new location about six weeks before the first hard freeze.
Q: When is the best time to cut back in the fall? A: “When they start to look too ratty for you and before the fresh new growth begins,” says Sarah. For plants that are frost-sensitive, wait until after the plants have gone through several hard frosts to ensure they're dormant before cutting back.
The best time to divide daylilies is either early spring, before the plants have begun to grow, or late fall, after the blooming season. Dividing daylilies is pretty straightforward. You'll need a shovel or spade, and a sharp dividing tool or pair of scissors.
Dividing Hostas in Fall
You should wait until night temperatures have cooled but while there is still time for divisions to grow new roots before freezing weather sets in. September is usually best in areas with cooler climates, October is okay for dividing hostas in warmer zones.
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.
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.
Divide fall blooming perennials in the spring because
New growth is emerging and it is easier to see what you are doing. Smaller leaves and shoots will not suffer as much damage as full-grown leaves and stems. Plants have stored up energy in their roots that will aid in their recovery.