11 Perennials I Cut Back in Fall — and the Ones I Leave Alone

11 Perennials I Cut Back in Fall — and the Ones I Leave Alone

Fall cleanup is one of those garden jobs that can get out of hand fast.

Once I have the pruners in my hand, it is tempting to start cutting everything that looks a little tired. Over the years, though, I have learned that a fall garden does not need to look perfectly cleaned up to be healthy.

In fact, cutting everything down can sometimes do more harm than good.

Here in Minnesota, September can bring warm days, cold nights, or our first frost. I have found it much more useful to watch what the plant is actually doing instead of deciding that everything needs to be cut back simply because the calendar says September.

If a perennial is still green and actively growing, I generally leave it alone.

If the foliage is yellowing, collapsing, diseased, frost-damaged, or clearly finished for the season, that is usually when I start cleaning it up.

These are the perennials I tend to reach for the pruners for first—and a few that I intentionally leave standing.

1. Peonies

Peonies are pretty easy for me to ignore for most of the growing season. By fall, however, their foliage usually makes it pretty obvious when they are finished.

Once the leaves have yellowed or frost has knocked the plant back, I cut the stems down to roughly 2–3 inches above the ground and remove the old foliage.

I pay particular attention to peonies that have developed spotting, mildew, or other foliage problems during the growing season.

Diseased foliage does not go into my compost.

I would rather bag it and remove it from the garden than give fungal disease another opportunity to hang around and show back up next spring.

The biggest thing with peonies is timing. If the foliage is still healthy and green, I leave it. Those leaves are still doing a job for the plant.

2. Hostas

Hostas can look beautiful right up until they absolutely do not.

A couple of hard frosts can turn those huge leaves into a collapsed, soggy pile almost overnight.

Once the leaves have yellowed, browned, or collapsed, I cut them back to around 2–3 inches above the ground and remove the old foliage.

I especially like getting that wet plant material out of the bed because decaying leaves create great hiding places for slugs and other pests.

What I do not do is cut down a healthy green hosta simply because September arrived.

As long as those leaves are green, they are still photosynthesizing and helping support the crown and roots. I let the plant tell me when it is finished.

3. Daylilies

Daylilies tend to start looking pretty tired by this point in the season.

You may have yellow leaves, old flower stalks, floppy foliage, and a plant that looks very different from what it did in June.

Once the foliage begins naturally yellowing and dying back, I cut it down to approximately 4–6 inches above the ground and remove dead, spotted, or damaged foliage.

Again, green leaves stay.

There is very little benefit to racing the plant to dormancy. If it is still green, it is still capable of feeding the root system.

4. Bee Balm

Bee balm is one I frequently notice from a distance and think looks perfectly fine.

Then I walk closer.

Powdery mildew.

Once blooming is finished and the foliage starts declining, I generally cut bee balm stems back to around 4–6 inches, particularly when mildew has become significant.

I remove the affected plant material instead of leaving it around the crown.

If your bee balm develops powdery mildew every single year, also look beyond the leaves themselves. A mature clump can become extremely crowded.

Thinning or dividing it can improve airflow around the plant, which can make a noticeable difference.

5. Garden Phlox

Garden phlox can be absolutely beautiful through summer and then look pretty rough by fall.

Powdery mildew is commonly part of the problem.

Once flowering has finished and the foliage is declining, I cut the stems back to approximately 2–4 inches above the ground and remove diseased leaves and stems.

Do not forget about the foliage underneath the plant.

If you cut away infected stems but leave a layer of diseased leaves sitting around the base, you have only completed half the cleanup.

I rake those out too.

6. Bearded Iris

Iris is one where I try not to get overly ambitious with fall cleanup.

The leaves can start looking ragged and tempting to remove long before the plant is actually finished with them.

While the foliage is still green, I leave it.

Once it yellows significantly or frost finishes it off, I cut the leaves back to around 6 inches and remove damaged, spotted, or dead material.

Fall is also a good time to actually look at the rhizomes.

Bearded iris rhizomes should not be buried deeply underneath soil or a heavy layer of mulch. They grow differently than a typical underground root or bulb, and the upper portion of the rhizome generally remains exposed.

Cleaning up the foliage also removes some of the old material where pests such as iris borers can overwinter.

7. Yarrow

Yarrow can go from upright and tidy to looking like it lost an argument with the wind.

Once flowering is finished and the stems begin browning, I cut the old flower stems back to a few inches above the healthy basal foliage.

I leave that healthy growth at the bottom instead of flattening the entire plant.

Yarrow can also be an enthusiastic self-seeder.

If you do not want baby yarrow plants coming up throughout the bed next spring, remove the flower heads before they have a chance to scatter mature seed.

If you do want more yarrow, this is one you can absolutely be a little less aggressive about deadheading.

8. Black-Eyed Susans

Black-eyed Susans are different because mine can still be putting on a pretty good show going into early fall.

I do not automatically cut them down in September.

Instead, I remove stems that are diseased, badly damaged, or clearly finished and leave healthy growth alone.

Later, once frost has finished the plant, stems can be cut down to around 3–4 inches above the ground.

But I rarely remove every seed head.

I like leaving some standing for the birds. Goldfinches and other seed-eating birds will work those flower heads over, and I would much rather have that winter activity in the garden than a completely empty flower bed.

9. Shasta Daisies

Shasta daisies are another perennial that can look fantastic through summer and progressively rougher as fall arrives.

Once flowering is over and the plant has begun naturally declining, I cut the finished stems back to roughly 2–3 inches, removing spotted or damaged foliage as I go.

If the middle of an established clump has become thin, woody, or bare, I make a mental note—or preferably an actual note—to divide it when the timing is appropriate.

An overcrowded older clump will often tell you it needs some attention.

10. Catmint

Catmint has a special ability to start the season as a beautiful rounded mound and finish it sprawled halfway across whatever is planted beside it.

After its main flush of flowers, I typically trim tired stems back by about one-third to one-half, cutting above healthy fresh growth rather than removing everything.

That cleans up the plant without taking away healthy foliage it can still use.

One thing I have found especially helpful is giving floppy catmint a haircut earlier in the season, immediately after its first major bloom.

It usually grows back shorter and bushier, and many varieties will reward you with another round of flowers.

11. Hardy Geraniums — Cranesbill

Hardy geraniums are excellent perennial ground covers, but by late summer or fall the plant can become a mixture of fresh leaves, old stems, declining foliage, and random flowers.

Instead of cutting the entire plant to the ground, I trim away the tired growth and cut scruffy stems back to just above healthier basal growth.

That gives the plant a cleanup while still leaving useful green foliage behind.

And one important distinction: when I am talking about hardy geraniums here, I mean cranesbill geraniums, not the colorful tender geraniums commonly sold as annual container plants in our area.

They are very different plants.

Perennials I Usually Leave Standing

There are several plants that I intentionally do less with in fall.

Unless there is a disease issue or another specific reason to remove the growth, I would rather leave them standing and clean them up later.

Coneflowers

I leave healthy coneflower seed heads standing.

They provide seed for goldfinches and other birds, add some structure to a winter garden, and there is no urgent reason for me to remove healthy stems in September.

I can cut them back later or clean them up in spring.

Sedum

I almost always leave upright sedum standing through winter.

Those dried flower heads actually hold their shape remarkably well, look beautiful with frost or snow on them, and give the winter garden some structure.

I cut the old stems down in late winter or early spring before the new growth really gets going.

Russian Sage

Russian sage does not get a major fall haircut from me either.

I leave the woody stems standing through winter and do the primary pruning in late winter or spring.

Hellebores

Healthy hellebore foliage can remain through fall and winter.

Older or battered foliage can be removed later as the new season’s flower buds and growth begin appearing.

Why I Don’t Cut Everything Down

The biggest lesson I have learned from working with plants is that a garden does not have to look spotless to be healthy.

Standing stems, dried seed heads, leaves, and other plant material can provide food and shelter for birds, pollinators, and beneficial insects.

That does not mean I leave diseased plant material lying everywhere.

There is a difference between leaving useful plant material and allowing a disease problem to remain in the bed.

My fall cleanup priorities are pretty simple:

I remove diseased growth.

I remove foliage that has completely collapsed and is creating a wet mess.

I clean up plants that are clearly dormant.

I leave healthy green growth alone.

And I keep seed heads or stems that have value for wildlife or winter interest whenever it makes sense.

The garden does not need to look freshly shaved going into winter.

September Means Something Different in Every USDA Zone

This is another reason I dislike gardening advice based entirely on a calendar date.

September in Minnesota is not September in Georgia.

For gardeners in USDA Zones 3–5, September can already bring very cold nights and the first frost. Once plants naturally yellow or frost knocks them back, fall cleanup can begin.

In Zones 6–7, September is often more of a gradual transition. Deadheading, removing diseased foliage, and cleaning up declining stems makes sense, while healthy green growth may continue working for quite a while.

In Zones 8–9, many perennials may still be actively growing or blooming. Fall cleanup is generally lighter, with more attention placed on spent flowers, damage, and disease rather than hard cutbacks.

And in Zones 10–11, September may behave much more like summer. Major pruning should follow the needs and natural growth cycle of the individual plant rather than a northern fall-cleanup schedule.

That is why my easiest rule is:

Watch the plant as much as you watch the calendar.

If it is still green, healthy, and growing, there is usually no benefit to being the first person in the neighborhood to cut it down.

A Little Fall Cleanup Goes a Long Way

Fall garden cleanup absolutely has value.

But more cutting is not automatically better.

Over the years, I have found that the best approach is usually to remove what is diseased, damaged, collapsed, or genuinely finished for the year and leave the rest alone until the plant—or our Minnesota weather—tells me otherwise.

Your garden may look a little wild going into winter.

That is okay.

A healthy garden is not always a perfectly tidy garden.

Once I have taken care of the plants that actually need attention, I step away from the pruners.

Sometimes that is the hardest part.

— Kristy Nohl
Bloom & Thorn Botanicals | All Things Succulents, LLC

For more straightforward plant-care information based on both plant science and hands-on experience growing plants in Minnesota, visit the Plant Care section at AllThingsSucculents.com.