15 Perennial Plants You Should Be Pruning In The Fall

Perennial plants can be trickier than annuals, because you need to learn how to help them thrive season after season. Knowing when and how to complete certain maintenance tasks is vital. And while many perennials grow best when they are pruned in the spring, winter, or summer, there are several that require autumn pruning. In fact, many perennials need to be cut back in fall, usually after they have finished blooming, to keep them happy, healthy, and thriving into the new year. Some of the plants you should be pruning in fall include popular hostas, classic peonies, and pollinator-friendly bee balm. 

Some of these perennial plants only require fall pruning if you live in certain areas, while others should be pruned in fall no matter where you live. Knowing when to prune can make the difference between a healthy plant versus a plant that fails to thrive. There are many other perennial plants that can be left alone in autumn to create beautiful, useful parts of a winter garden. Pay attention so you can avoid cutting back plants that don't need it, and make sure to prune the plants that will benefit.

One of the biggest mistakes to avoid when growing hostas is to not prepare them properly for winter. These perennials thrive even into hardiness zones 3 to 4. But to keep them coming back every year, it's best to cut back foliage. Pruning hostas can be done in fall, typically after the fall color is gone or after a hard freeze. The leaves should turn almost fully yellow and brown, indicating it's time. Removing the dead stems, leaves, and leftover flower stalks will make it easier to weed around bushy hostas.

In the autumn, common yarrow (Achillea millefolium) benefits from selective pruning. Cut back all but the basal leaves. Some gardeners might keep the seed heads and stems to add winter interest, but removing them limits its aggressive self-seeding habit. Cutting back the stalks also combats mold and disease. A tip to remember where your yarrow is planted is to leave a little bit of stem, about 6 inches, during autumn pruning. If there is disease present, always cut back the entire plant to the ground. Yarrow is hardy in zones 3 through 9.

Bee balm (Monarda spp.) attracts bees and hummingbirds and features in a range of species and cultivars. Hardy in zones 4 through 9, bee balm holds up well to pruning in late spring to early summer. Thinning out stems allows for better airflow. Further light pruning in fall helps shape it during dormancy. However, if your bee balm plants have any signs of powdery mildew, you need to remove all diseased foliage or even cut back the entire plant. Resistant varieties may even develop this nasty fungus in harsh autumn and winter conditions.

While many perennials provide great winter habitat for birds, others do not. Lungwort (Pulmonaria spp.), including common lungwort (Pulmonaria officinalis) and other cultivars, can be added to your list of plants to prune in fall, because it will save you time in the spring. Unlike some plants whose foliage should be left alone to protect the plant in winter, lungwort will come back fine the next year and it's hardy from zones 3 through 8. But if your area has warmer winter temperatures, skip fall pruning and grow lungwort as an evergreen.

Salvia (Salvia spp.) make excellent additions to a perennial flower garden in certain climates, including woody salvia species like autumn sage (Salvia greggii) and deciduous species like pineapple sage (Salvia elegans). Pruning time depends on your growing zone and how cold the temperature dips in winter. For both types of salvia, those who live in areas without the risk of frost damage should prune in late fall. Woody salvia stems should be cut down 5 to 8 inches. 

A showy and elegant flower that is hardy in zones 3 to 10, bearded irises (Iris germanica) depend on regular deadheading and maintenance. In fall, however, spend some time cleaning them up in your garden. Irises easily experience rot and infestation by pests like the iris borer. Following a hard freeze in the fall, you can cut off the top of your bearded irises, leaving about 1 to 6 inches of the leaves above the ground. Be careful about disposing of the dead plant material, especially if it shows signs of disease.

Delphinium, or larkspurs, include over 500 different species, including many perennial varieties. This tall, stately flower is an example of a perennial that does well with careful maintenance, such as dedicated pruning at different times each year. Typically, cutting back the entire plant after it blooms encourages another show of flowers later in the season. After this second bloom has finished and the entire plant has wilted, it's best to chop the whole thing straight to the ground. Delphinium is typically hardy from zones 3 to 9.

A charming garden classic, the romantic peony (Paeonia spp.) is a delightful perennial, whether its the woodland species (Paeonia japonica) or the garden peony (Paeonia spp. hybrids). A common mistake everyone makes when pruning peonies is to not properly prune in autumn. Peonies can be cut back after a hard freeze down to the soil. They do best in zones 3 to 8, so the first hard freeze will differ depending on location. Dispose of diseased plant debris to avoid spreading disease. Tree peonies (Paeonia suffruticosa) are shrubs and should not be cut back.

Some perennials do well with a spring cleaning, but fragrant tall phlox (Phlox paniculata), a gorgeous garden flower that keeps hummingbirds visiting past summer, should be pruned in fall. Tall phlox is perhaps the most common species and is hardy from zones 4 through 8. Unfortunately, it can be beset with powdery mildew and infected foliage needs to be removed and disposed of promptly. After the end of its bloom time, cut the stems back to manage this issue.

The native black eyed susan (Rudbeckia hirta) is one of the best perennials to leave standing after they bloom. A fast-growing flower, they are hardy in zones 3 through 8. They can provide an excellent source of food for birds in late autumn and early winter. But you should always prune black eyed susans and any other perennials that show clear signs of disease. Infected leaves may feature black spots or lesions. Do not just remove the infected parts. The entire plant should be cut down in fall to prevent the return of the disease.

If you want an easy-to-grow perennial, speedwell (Veronica spicata) is a good choice. It is hardy from zones 3 to 8 and maintenance is relatively simple. Speedwell is an example of a perennial that has no utility to the garden in fall, serving no aesthetic use or as a food source for birds. Depending on preference, you can choose to cut the plant back after its finished flowering, leave pruning until spring, or wait until a hard frost. When pruning, remove the dead leaves and cut the stems down to about 2 inches. 

A pretty perennial with a classic look, shasta daisies (Leucanthemum x superbum) are hardy from zones 4 through 9. When the seasons change, it's time to prune your daisies to prepare for future growth. Wait until after the flowers are completely spent and there are no more blooms. New basal leaves sometimes emerge in late fall, which stay on the plant until spring. When pruning, only remove the flower stalks.

The swamp mallow (Hibiscus moscheutos) looks like a shrub, but it's actually a herbaceous perennial. Hardy in zones 4 through 9, rose mallows do well with regular pruning and deadheading. In late fall, however, it's an example of a perennial that needs to be cut back in autumn for optimum growth. In fact, flowers only appear in spring on new growth. For best results, the stems can be cut back almost to the ground, leaving about 3 to 4 inches.

One gardening mistake that can hinder the growth of your daylilies (Hemerocallis spp.) is not pruning when you should. Daylilies do not have many issues, but prompt removal of foliage can prevent one common pest: The slug. Hardy from zones 3 through 9, wait until a hard freeze destroys the foliage before cutting them back. It's also important to note that daylilies left alone in the winter garden add little to the scenery. You can wait until spring to take care of the old plant matter, but there's more risk of disease or pests.

Similar to astilbe, goatsbeard (Aruncus dioicus) is larger with tall, white plume-like flowers. Hardy in zones 3 through 7, goatsbeard can be cut back in either fall or spring. Because of its extensive growth habit, some gardeners may prefer autumn pruning. When cutting this perennial back, prune the stems back to ground-level, but only after the plant has entered its dormant period. Dormancy typically comes after the first hard frost. A little compost applied around the base is beneficial, or add some natural leaf mulch.