What Perennials To Cut Back In The Fall

Autumn comes along with many responsibilities around the house, especially if you’re an avid gardener. The season marks the time when many plants become dormant and no longer look healthy. That’s why so many homeowners and gardeners struggle with what perennials to cut back in the fall.

Phlox, bearded iris, catmint, and yarrow are some of the most important perennials to cut back in the fall. Perennials like false indigo, blazing star, salvia, and yarrow must be cut back to protect them from cold temperatures. It’s essential to inspect your perennials for signs of disease and fungus, such as moldy mildew, and prune them as needed.

Make sure to thoroughly water your perennials before you cut them back. It’s also important to cut your perennials back before the first frost of the year. Otherwise, it may be too late. Follow along as we explore what perennials to cut back in the fall.

What Perennials Should You Prune In The Fall?

1. Phlox

Phlox is one of the most vibrant, popular plants, and it’s a fixture in countless gardens. That said, phlox goes dormant between fall and early spring like many perennials. Some homeowners don’t cut phlox back, and that’s fine in some cases.

However, you must prune phlox if you find traces of powdery mildew. This harmful fungus can hinder the growth of any plant, and it’s common with phlox. Carefully prune your phlox before the first frost of the year for the best results.

2. Bearded Iris

Bearded iris is a relatively sensitive plant when it comes to diseases, fungus, and growth problems. For example, many gardeners prune bearded iris shortly after it blooms to avoid problems. Luckily, you can enjoy some healthy, vibrant foliage until the end of the summer or mid-September.

Carefully cut back 6” of the leaves, or more if it’s a large plant. It’s a great idea to water your bearded iris before you prune it. However, you must never water a bearded iris if the first frost of the year has already hit.

3. Catmint

While you can trim catmint year-round, it’s essential to cut it back by the fall. Otherwise, the plant can go into shock from frost damage if it has too much dead growth. Cutting it back is a great way to ensure that your catmint will thrive when it’s time for spring.

Catmint does best between zones 4 and 8, but climate isn’t a factor if you grow it indoors. Make sure you don’t prune too much, or else you may damage the plant. Put your catmint in a spot with plenty of sun when spring comes around, even if it can tolerate partial shade.

4. Yarrow

Yarrow is one of many perennials that looks great during the spring and summer but looks dead during winter. While it isn’t likely dead, yarrow appears dead during the fall and winter because it goes dormant. Ideally, you should cut yarrow to stand 6” to 12” above the ground.

Otherwise, you can transplant the yarrow and bring it inside to grow throughout the fall and winter. However, it requires caution, as transplanting a yarrow can make it go into shock if you aren’t careful.

5. Blazing Star

Some gardeners jump the gun too early and prune blazing stars once flowering is complete. However, that isn’t necessary, and it can hinder the plant’s growth. Instead, it’s best to wait to cut your blazing star back until the first frost of the year is approaching.

For the best results, you must cut your blazing star to roughly 2” above the soil. That may seem excessive, but it will quickly recover by the spring if you water it thoroughly before the first frost.

6. Salvia

If you don’t cut salvia back in the fall, you risk ruining its appearance. Failure to deadhead salvia results in unattractive, woody stems that may struggle to grow. Salvia is one of many perennials that you can trim so low that it’s close to the soil. Otherwise, you can simply remove dead leaves and twigs before they naturally fall off.

7. Bee Balm

Much like phlox, bee balm is susceptible to powdery mildew, and it cannot survive the fall under those conditions. Whether bee balm has mildew or not, it’s still a great idea to cut it back in the fall. Deadheading bee balm in the fall is essential as the dead growth can hold it back.

Bee balm doesn’t typically bloom until July, so you must do whatever you can to protect it until then. Don’t compost or put bee balm trimmings near your other plants if you discover signs of powdery mildew. 

8. Peonies

Peonies are yet another perennial plant that can suffer from powdery mildew. That’s why it’s best to cut peonies back before the fungus has the chance to spread to nearby plants. It’s still a great idea to prune peonies in time for the fall even if they don’t have powdery mildew.

While they look great in bloom, peonies appear to be dead when they are dormant in the fall. Some people bring peonies indoors to avoid this problem, but that’s often a bad idea. That’s because cold periods are a natural part of the life cycle of peonies.

9. False Indigo

False indigo, also known as baptisa, is instantly recognizable for its blue flowers and green leaves. However, it will lose color and look bad when it gets close to the first frost of the year. The leaves will wilt and turn brown, but luckily, that makes it easier to tell where you should prune them.

Don’t wait too long, or the leaves will turn black once the ground freezes. You won’t have to wait too long for it to grow back, as false indigo typically blooms in mid-to-late spring.

10. Astilbe

Astilbe has beautiful flowers, but they quickly fade once autumn begins. The best way to ensure this perennial comes back is to cut it short in early fall. You can cut astilbe so short that it is essentially tiny stems.

That may seem excessive, but your astilbe should survive if the root system is intact. It’s a great idea to nourish the astilbe with fertilizer and compost before you cut it back.

11. Crocosmia

Crocosmia is one of many plants you must prune several times throughout the year. For example, many gardeners prune crocosmia once the bloom cycle is done. That is the best way for blooms to appear, but it isn’t required.

However, autumn is the one time of the year when it’s essential to cut crocosmia back. While you don’t need to cut too much off during the spring and summer, you must cut it short in early autumn. For the best results, you must cut crocosmia to stand 1” to 3” above the soil in the fall.

12. Goldenstar

Known for its vibrant yellow flowers, it isn’t always necessary to cut Goldenstar back in the fall. While you should prune it a bit, you may not need to cut it back as much as crocosmia and similar plants. However, you must cut crocosmia low if you find signs of disease and fungus.

Like phlox and bee balm, Goldenstar is prone to powdery mildew, which can eventually kill it. If your Goldenstar is healthy, you must only prune dead leaves when you cut it back in autumn.

Are There Any Perennials That Should Not Be Cut Back In The Fall?

Plants like stonecrop, lavender, and milkweed should not be cut back in the fall. Such plants do better in cold weather if they are largely intact. It’s also a bad idea to deadhead Lenten roses, as they handle cold weather much better than other perennials.

That said, you can prune dead leaves if you leave the stalk and stems intact. Avoid cutting back ornamental grasses as well, because they can withstand cold temperatures, rain, snow, and even ice.

Summing It Up

While you don’t need to cut back all your perennials, it’s a great idea to deadhead Goldenstar, phlox, and bearded iris in autumn. Peonies, bee balm, salvia, and false indigo require pruning before the first frost of the year. Cut back any plants that you see with signs of disease and fungus before the temperatures drop too low.

Related Guides:

• Flowers That Can Survive A Spring Frost
• When Should You Move Plants Inside?