While perennials are both beautiful and reliable, one thing about them is that they do require regular trimming. And some might need it more frequently than others!
In today’s article, let’s walk through a specially curated list of perennials you can trim in September to achieve a better flower show next spring.
Why Early-Fall Is The Prime Time For Cutting Back
In some regions, the month of September usually means early fall. By September, cooler nights have arrived, and in colder zones the first light frosts may already be showing up.
Removing spent foliage allows for the prevention of harmful diseases and pest populations while also promoting healthy new growth.
You might also like this guide on which flower seeds you can still collect in September.
Perennials To Cut Back In Early-Fall
1: Peonies (Zones 3-8)
Peonies are cold-hardy perennials that are quite susceptible to pests and fungal issues. You should trim them in fall to limit fungal diseases and allow their crowns to rest without unwanted hindrance.
For step-by-step guidance, check out this handy guide on what to do with peonies after flowering, it walks you through timing and what to do with the foliage.
2: Hostas (Zones 3-9)
After the first few frosts, the foliage of hosta plants starts to become mushy and attract tons of slimy slugs. Cutting back in September keeps these problems at bay.
3: Daylilies (Zones 3-9)
If you didn’t already know, daylilies are super adaptable perennials, meaning they can grow in pretty much any environment or soil conditions. Trim spent foliage off your daylily plants in September to not only give the garden a neater look but also reduce the risk of harmful diseases.
And if you’re also sowing crops this month, here’s a list of herbs you can direct sow in September for a spring harvest.
4: Bee Balm (Zones 4-9)
In milder zones, it’s a good idea to trim bee balms in September as they’re a lot more susceptible to fungal problems like powdery mildew in fall.
For a wider look at the do’s and don’ts, here’s a full guide on what to cut and what to leave in September
5: Tall Garden Phlox (Zones 4-8)
Like some of the other perennials on this list, garden phlox is also sensitive to fungal infections. A fall cutback mitigates the risk of powdery mildew and self-seeding significantly.
6: Bearded Iris (Zones 3-10)
Cut your bearded iris foliage down to 6 inches after the blooming season ends to limit potential pest problems and rot.
7: Lavender (Zones 5-9)
In the case of lavender, fall trimming should be very light and subtle. DO NOT cut back too much of the foliage as the perennial will be entering dormancy soon.
8: Yarrow (Zones 3-9)
Because yarrows tend to spread fast and aggressively, you want to trim them right after they’re done flowering to make the garden tidier and encourage fresh growth in the perennial.
Want more early-fall bloomers? Here are 11 flowers to plant in September for a gorgeous spring display.
9: Black-Eyed Susan (Zones 3-9)
With black-eyed Susans, you’ve got two choices: cut them back now to reduce reseeding and disease, or leave the seed heads standing to feed birds through winter, which, in my opinion, matters more than simply tidying the garden.
Either way works, it just depends on your goals. The choice of whether to trim or not is totally yours!
If you decide to tidy them, here’s a September deadheading guide to help you choose what to cut and what to leave for the birds.
10: Spike Speedwell (Zones 3-8)
During growth and blooming, spiked speedwells can become quite messy and untidy. After blooming, cut the perennial back to basal foliage for a neater winter look and to promote new spring shoots.
11: Globe Thistle (Zones 3-8)
After globe thistles bloom, they leave behind dried seed heads that should be cut in fall to prevent reseeding and tidy up the patch.
And for another angle, here are perennials you should divide in September to keep them healthy and blooming.
Some Perennials You Must Leave Alone
Perennials like coneflowers, black-eyed Susans, and sedums not only add beauty to your garden in the wintertime but also provide seeds for birds.
Russian sage and butterfly bush are two perennials that should only be cut back in early spring once new growth starts to set in.
Astilbe, coral bells, and hellebores need their foliage for support in the winter and should be trimmed right before new spring growth emerges.
Tips By USDA Zone – When To Cut Back In Your Area
Let’s Conclude
While many might speculate and tell you that cutting back your perennials in September probably isn’t a good idea, I’m here to tell you that it probably is!
The early fall time not only accommodates the regrowth of the perennials perfectly but also ensures your garden landscape will be tidy and pleasant-looking going into winter.
If you’d like more color that lasts, take a look at these fall-blooming flowers that keep going through frost
I live in Massachusetts what about tall
Ornaments grasses, when ahould they be trimmed
Hi Karen! 😊 In Massachusetts (Zone 5 to 6), it’s best to leave tall ornamental grasses up through winter, they add beautiful texture and protect the crown from cold. Then trim them back in late winter or very early spring, just before new growth starts pushing up. I do mine around March!
this is really helpful, thank you. Some I knew about, other’s not. I am in zone 5 a/b
I will put this link on my blog, as I have a number of other people who would find this useful.
Hi Gill! That’s so kind, thank you! 😊 I’m really glad it was helpful, and I appreciate you sharing the link on your blog. Hope it helps your readers too, especially in Zone 5!
Show the map with zones please
Hi Judy! We can’t publish the map but you can just Google your ZIP code + “USDA zone” and it’ll show you exactly where you fall on the zone map! Super helpful for knowing what to plant and when 😊
I planted phlox, clethera and a northern sea oats this month. Should I wait till next fall to cut them back?
Hi Linette! 😊 Since you just planted them, I’d wait until next fall to cut them back. Let them keep their foliage through winter so the roots can settle and get stronger first.