12 Perennial Plants To Avoid Pruning In The Fall At All Costs

Pruning is an important task to help ensure plant health and keep the perennial garden thriving. In my work as a professional gardener, I try to observe the recommended guidelines for pruning shrubs and trees, which usually follow specific seasonal timing. For example, lilacs need to be pruned soon after blooms fade before new buds start to form. But perennials are usually dealt with in a more casual way in this regard, with many gardeners pruning things back in the fall during their annual clean up. But there are good reasons for observing proper timing when pruning your perennials, and there are a number of plants that should not be pruned in the fall, so let's look at them.

One reason to avoid pruning certain perennials in autumn is that pruning may make the plant vulnerable in winter weather, which can affect new spring growth, or even weaken or possibly kill the plant. This includes butterfly bushes, coral bells, and sedums: All are fairly tough plants, but they'll thrive better with proper pruning, so it's best to leave them intact and wait until early spring to prune these plants in order to make room for new growth.

Another reason to avoid pruning certain perennials in the fall is that they may provide important food for wildlife, such as seeds, cones, or berries. This includes coneflowers, black-eyed Susans, butterfly weed, and beautyberry. Some plants also provide bird-friendly winter habitat, giving shelter and cover from cold, windy weather. Last but not least, some perennials add beauty and texture to the landscape if left intact until spring, like sedums, false indigo, and globe thistle.

Coneflowers (Echinacea) are wonderful hardy perennials that bloom for weeks from late summer into autumn. Many varieties have prominent seed cone centers (giving them their common name) and these seeds are loved by many songbirds. If your coneflower blooms start to fade in late summer, you can trim a few off to keep the plant neat and stimulate more buds, but be sure to leave the largest blooms intact for winter wildlife food, and cut them back in spring to stimulate new growth.

Yarrow (Achillea) is a popular summer-blooming perennial for the cottage garden. Its herby scent repels many insect pests, and the flowers last for weeks in the garden. Deadheading spent flowers will encourage repeat blooms, and it's best to remove the faded, brown foliage, but when yarrow forms new clumps of green foliage in late summer, leave this intact to protect the plant's roots through winter.

Sedums are sturdy, robust perennials with three seasons of interest — keep them intact through winter and that makes four! The taller upright varieties (like 'Autumn Joy, 'Neon,' or 'Matrona') provide nice winter interest in the landscape, as well as shelter for birds and wildlife, and help to protect the base of the plant through the winter. You can help these plants thrive by leaving the stems intact until the new cabbage-like buds emerge in spring.

The tall, airy flower stalks of Russian sage (Salvia yangii) are excellent pollinator magnets in late summer, attracting many varieties of bees, butterflies, and moths. Though the faded stalks are not as attractive as the pale purple flowers, it's good to leave them unpruned until new spring growth emerges. Pruning Russian sage in spring ensures a healthy start to new flower stalks.

Since asters are late season flowering plants, pruning them too soon after the blooms fade can leave the plants vulnerable. This is because the plants expend a lot of energy putting out blooms well past frost. The seeds are also loved by many foraging birds in winter including nuthatches, cardinals, and chickadees. To provide some food for birds in cold weather and keep your asters healthy, it's best to delay pruning until early spring when you start to see new green shoots emerging. 

Once it's established, lavender (Lavendula augustifolia) is a great perennial herb producing fragrant flower stalks that perfume the garden and repel mosquitoes. Though deadheading spent flower stalks in summer can help encourage reblooming, avoid doing any heavier pruning until spring. The woody stems of lavender should be cut back to help maintain the plant's shape and encourage healthy new growth, but doing so in fall can leave the cut stems vulnerable to cold temperatures. It's best to wait until early spring to prune it, just as new growth starts to appear.

Like asters, mums (Chrysanthemum) are late season bloomers. While deadheading the spent flowers is encouraged, perennial mums should be left mostly intact through winter and cut back in spring to make room for new growth. If you plant nursery mums in your garden in fall, be aware that the larger "bushel" plants may not be very robust and the stems may dry out and break off on their own. This is why I encourage getting bare root mums via mail order to plant in spring or purchasing smaller potted ones for planting in late summer.

The pollinator-attracting butterfly bush (Buddleia davidii) is technically more of a "shrubby" perennial than a perennial shrub. There are many compact hybrid cultivars available now, but some older varieties will tend to grow quite large if you don't prune them every year to control size. The best time to do this is in spring, just as the new growth starts to appear. Cut back the dead branches and new ones will grow to fill in. This helps to encourage better branching with more blooms, too. Light deadheading in the fall will keep it looking neat.

Beautyberry (Callicarpa americana) is a lovely shrub with purple berries in later summer through fall. Since these berries attract songbirds and also provide a good winter habitat, it's best to leave them intact and prune in the spring. It's important to prune them regularly (once per year) as the branches can get quite dense and may crisscross each other if they're left too long.

Black-eyed Susans (Rudbeckia hirta) are a well-loved perennial for their striking golden-yellow color in the late summer landscape. The center cones provide seeds eaten by a number of birds, so leaving them whole as the season winds down ensures some food for wildlife. These can be easily cut back in spring when you do spring clean up. The one exception to this rule is that, if you don't want them reseed too much in the garden, you may want to remove some of the flower heads before they go to seed.

Peonies (Paeonia) are long-lived perennials that can last for decades in a suitable location with good soil conditions. Though the leaves do tend to turn brown in autumn, it's best not to cut these all the way back until early spring when new growth begins to show. Most gardeners deadhead the spent flowers in summer. I will sometimes cut back a few of the leaves to create some space in the late summer garden, but I leave the stems and the lower leaves intact and let them die back naturally over winter, then trim them in spring.

Coral bells (Heuchera) are terrific perennial suitable for semi-shaded or partly sunny garden beds. The lower leaves tend to get a bit messy at the end of the season, but it's best to wait until spring to clean them up when the new growth has begun to avoid having the crowns be vulnerable in winter weather. New growth on coral bells starts in the middle at the crown, and is usually a bright fresh foliage color, so it's easy to see when it's time to trim those old leaves.