11 Summer-Blooming Plants You Should Cut Back in September

Are you wondering whether it’s time to cut back certain plants? September is a great time for clipping many summer bloomers. Whether you hope to increase conditions where a second set of blooms forms, or you’d like to keep your plants tidy, it’s good to know which to trim.

Some plants are sensitive to being cut back ahead of cooler seasons. It’s best to leave them alone and let them do their thing until the first frost comes. But there are plenty of plants that appreciate pruning as the summer turns to a more temperate autumn. 

We’ve gathered together a list of 11 summer-blooming plants you should cut back in September. The reason for pruning them varies, but they all like to get a snip this month. Whether it’s vigor or even another set of blooms, don’t forget to snip these guys!

Colorado Blend Yarrow

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Munstead Lavender

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Lavender

	botanical name Lavandula spp.
	sun requirements Full sun to partial shade
	height 1-3’
	hardiness zones 5-9

Fall is my favorite time for so many reasons, one of them being that my Mediterranean herbs are about to pop off. Lavender is one such plant. As the cooler weather comes on, if I deadhead my lavender and give it a little pruning, it simply takes off in fall and winter.

Mind you, I live in an area that has milder winters than most, in zone 8b. For those in colder areas, it’s better to hold off and focus on sheltering through the cold. If you live in an area where there are still several weeks before the first frost, cut back these plants in September. 

Lavender does best when you prune it in spring, but in delayed winter areas, prune away spent flowers, and prune it back to ⅓ the size of the plant. This keeps it vigorous and happy in fall, which can be like a second spring in temperate regions.

Catmint

	botanical name Nepeta spp.
	sun requirements Full sun
	height 1-2’
	hardiness zones 3-8

Much like lavender, catmint (or catnip, depending on which species you grow) appreciates some cutback in milder areas. Clip away spent leaves, and get those plants cut back. September is the perfect time to do this. 

If you take about ⅓ of the plant as you prune, feel free to collect the leaves for tea or give them to your cat. Hang bundles around the house to dry, and water propagate some of the clippings to make even more plants. It doesn’t hurt to harvest catmint as often as you’d like throughout the season. But a hefty trim ahead of fall is a good idea. 

If you live in a cold region in which winter is just a couple of weeks away, ensure your catmint is covered or moved indoors out of the cold.

Salvia

	botanical name Salvia spp.
	sun requirements Full sun
	height 1-3’
	hardiness zones 5-10

Salvia should be pruned heavily in the fall, and with the autumnal equinox sitting right at the end of September, this month is a great time to do it. Depending on the type of salvia you have, there are different ways to prune. If you’re working with a woody specimen (like S. greggii), prune back the plant to about six inches tall. 

For rosette or clump-forming salvias (S. nemorosa, S. sylvestris and superb), there aren’t branches to prune. In this case, leave the leaves at the base, and remove any spent flower stems. This makes way for another set of blooms in mild areas, and prepares the plants for winter dormancy in colder ones. 

Coneflowers

	botanical name Echinacea spp.
	sun requirements Full sun to partial shade
	height 1-5’
	hardiness zones 3-9

Coneflowers are a stunning display in areas that don’t have a fall freeze. They really appreciate deadheading in these regions in order to produce a second set of blooms before the cold comes in. Much like clump-forming salvias, in cold areas, removing browned flower stems promotes root development needed for dormancy. 

However, you may choose to leave a few seedheads on the plants over winter to feed songbirds. The hollow flower stems also offer shelter to overwintering solitary bees and other beneficial insects. Seeing the winter’s light through the coneflower seedhead is a source of interest when other plants are doing nothing, too. 

Mistflower

	botanical name Ageratina havanensis
	sun requirements Full sun to partial shade
	height 3-5’
	hardiness zones 7-11

White mistflower is one of the best sources of nectar for butterflies. Its tiny flower clusters bloom readily in spring through summer, and then put on a second set of blooms in fall. When is the best time to get these plants cut back? September is the month to do it! This gives the plant a little lift before it blooms again in fall. 

If you live in the pathway of migrating butterflies, it’s essential to carry out this task. When they get to your garden, you want them to have the energy they need to make their long trek to their next destination. Especially if you live in the temperate regions of North America, this is a great plant to have. 

Yarrow

	botanical name Achillea millefolium
	sun requirements Full sun
	height 1-3’
	hardiness zones 3-9

Because they bloom throughout the year, get your yarrow plants cut back in September. Simply snip the browned seed heads and collect the seeds. If you live where fall is not as cold, you’ll see more blooms up until the first frost. 

If you live in a colder region, cutting back these plants in September ensures the ferny rosettes are ready for the oncoming frost. While pretty much any of the plants on this list can provide habitat if they aren’t cut back, yarrow is one of the most ecologically generous ones. It will colonize areas, keeping annual invasive weeds away, and its stems are perfect for insects. 

Bee Balm

	botanical name Monarda spp.
	sun requirements Full sun to partial shade
	height 2-4’
	hardiness zones 3-9

Especially when it comes to powdery mildew-prone bee balms, you should have a time set aside to get those plants cut back. September is a good time for gardeners in colder regions. Use this month to gather any last bits for using in tea and in the kitchen in general. 

In milder places, deadhead your monarda to promote a second set of blooms. Collect any leftover seedheads from species that flowered and faded in summer, or leave them to self-seed. If you’ve planted powdery mildew-resistant bee balms – like Monarda fistulosa ‘Claire Grace’ or ‘Grand Marshall’s’ – your prune is a preparation for dormancy. 

Phlox

	botanical name Phlox spp.
	sun requirements Full sun to partial shade
	height 3-5’
	hardiness zones 3-9

Many species of phlox need to be tidied at the end of their season. Some are highly susceptible to powdery mildew, and some are simply browned and ready to be revived. Cut them back to about six inches above the ground, and ensure that any mildewed foliage ends up in the trash, rather than the compost pile. 

If you’re in a region where Phlox paniculata is native, giving it a trim increases the chances of another set of blooms. Just remember to cut them down at the end of the season to keep mildew out of the garden for good.

Clematis

	botanical name Clematis spp.
	sun requirements Full sun
	height 1-20’
	hardiness zones 3-9

If you’re growing herbaceous clematis species, it’s time to get those plants cut back. September pruning of these clematis falls right in line with their growth habit. Cutting C. heracleifolia, C. integrifolia, and C. recta down to the ground keeps the plants in good health. 

All other types should be pruned after flowering or in dormancy. Determine which type you have before giving them a September chop. You don’t want to prevent flowering next season or reduce the vigor of the vines overall.

Wormwood

	botanical name Artemisia spp.
	sun requirements Full sun to partial shade
	height 1-4’
	hardiness zones 3-8

While it doesn’t always produce flowers outside its native range, wormwood is one of those plants that likes a prune after it blooms in summer. When is the time to get these plants cut back? September is the time! For some varieties and species, it’s best to prune only new green growth and leave woody parts alone. 

September snips on your wormwood are great for tidying up the plant. Look for dead, diseased, and dying areas, and remove those first. Then prune back the green tips to promote more vigorous growth, whether it’s coming later in your mild fall or emerging after the cold in spring. Use the sprigs for wreaths. 

Of course, if you’re dealing with an invasive wormwood, knock that baby out! It’s totally ok to go to town on wormwoods that are pushing out valuable native plants. 

Coreopsis

	botanical name Coreopsis spp.
	sun requirements Full sun
	height 1-3’
	hardiness zones 3-9

Much like many others on this list, coreopsis needs pruning as summer ends to promote vigor. Get those plants cut back! September pruning of coreopsis ensures it blooms again in milder regions. In cold ones, it prepares the plant for winter dormancy, prompting deeper root growth for survival. 

I usually have no problem with coreopsis spreading around where it wasn’t planted. So your pruning this month could simply be for removing seed heads that pop and self-sow all over the place. Collect the seeds, direct sow them elsewhere over fall and winter, and they’ll get the proper cold period they need to sprout.