Are you wondering if it’s time to grab those garden shears and start snipping?
September marks a pivotal moment in the gardening calendar when many summer bloomers benefit from strategic pruning.
But which plants should you cut back, and which ones prefer to be left alone until frost arrives?
Today, we’ll explore ten summer-flowering plants that thrive with September pruning.
Whether you’re hoping to encourage a second flush of blooms or simply preparing your garden for the cooler months ahead, these plants will reward your September snipping efforts with renewed vigor and better winter preparation.
1. Lavender (Lavandula spp.)
Let’s start with everyone’s favorite Mediterranean herb! If you’re growing lavender in zones 5-9, September offers an excellent opportunity for strategic pruning, especially if you live in milder winter regions like zones 8-9.
While spring remains the ideal time for major lavender pruning, gardeners in areas with delayed winters can benefit from September deadheading and light trimming. Remove spent flower spikes and prune back about one-third of the plant’s size. This encourages vigorous fall growth when cooler temperatures arrive – think of it as a second spring for your lavender plants.
However, if you’re in colder zones where frost arrives early, focus instead on protecting your plants through winter rather than stimulating new growth that might not harden off properly before freezing temperatures hit.
2. Catmint (Nepeta spp.)
Does your catmint look a bit raggedy after a summer of constant blooming? September pruning works wonders for these hardy perennials. Cut back spent foliage and flower stems by about half, and you’ll often see fresh growth emerging within weeks.
Here’s a bonus tip: those clippings don’t have to go to waste! Bundle the aromatic stems and hang them to dry for homemade cat toys, or steep the leaves for a soothing herbal tea. You can even try water propagating some of the healthier stems to create new plants for next season.
In zones 3-8, catmint handles September pruning beautifully, but gardeners in the coldest regions should ensure adequate winter protection for newly trimmed plants.
3. Salvia (Salvia spp.)
The pruning approach for salvias depends entirely on which type you’re growing, but September timing works well for most varieties across zones 5-10.
For woody salvias like Autumn Sage (Salvia greggii), cut the entire plant back to about six inches tall. This dramatic pruning might seem severe, but these tough plants respond with vigorous new growth.
Clump-forming salvias such as May Night (S. nemorosa) or Wood Sage (S. sylvestris) require a different approach. Instead of cutting back branches, simply remove spent flower stems while leaving the basal foliage intact. This selective pruning often triggers a spectacular second bloom period in mild fall weather.
4. Coneflowers (Echinacea spp.)
Should you deadhead those spent coneflower blooms, or leave them for the birds? The answer depends on your priorities and climate zone.
In regions with extended growing seasons, September deadheading encourages coneflowers to produce another round of blooms before winter dormancy. Simply cut back the brown flower stems to the nearest set of healthy leaves.
However, you might choose to leave some seedheads standing through winter.
Those spiky centers provide valuable food for goldfinches and other seed-eating birds, while the hollow stems offer shelter for beneficial insects.
It’s a beautiful balance between garden tidiness and ecological value.
For gardeners in zones 3-9, coneflowers handle September pruning well, though those in the coldest zones should focus on root development rather than encouraging late-season blooms.
5. White Mistflower (Ageratina havanensis)
If you live along butterfly migration routes, this native perennial deserves special attention in your September garden tasks. White mistflower provides crucial nectar for migrating monarchs and other butterflies making their epic journeys south.
Cut back spent blooms and leggy growth in September, and you’ll be rewarded with a fresh flush of the tiny white flowers that butterflies find irresistible. This timing is particularly important in zones 7-11, where fall blooming coincides perfectly with peak migration periods.
The plant’s common name comes from its misty appearance when covered in countless small white blooms – a sight that’s even more spectacular when covered with feeding butterflies.
6. Yarrow (Achillea millefolium)
Yarrow’s ferny foliage and flat-topped flower clusters make it a garden workhorse, but September pruning keeps it looking its best. Cut back brown flower heads and collect the seeds if you want to expand your yarrow colonies naturally.
In milder climates, this pruning often results in additional blooms lasting until the first hard frost. Cold-climate gardeners benefit from September cutbacks that prepare the attractive rosettes for winter survival.
Here’s something fascinating about yarrow: when left unpruned, it becomes an ecological powerhouse, providing habitat for beneficial insects while colonizing areas and preventing invasive annual weeds from establishing. Those sturdy stems offer winter shelter for many garden allies.
7. Bee Balm (Monarda spp.)
Bee balm presents a special case for September pruning, particularly if you’re dealing with powdery mildew issues.
This native mint family member is beloved by pollinators but can struggle with fungal diseases in humid conditions.
For disease-prone varieties, September offers an ideal time to cut plants back and remove any mildewed foliage.
Make sure diseased plant material goes in the trash rather than your compost pile to prevent reinfection next season.
If you’re growing newer, mildew-resistant cultivars like ‘Claire Grace’ or varieties of wild bergamot (M. fistulosa), you can focus on deadheading spent blooms to encourage fall flowering in milder regions.
Don’t forget to harvest some leaves for tea before you prune – bee balm makes a delicious and aromatic herbal brew.
8. Garden Phlox (Phlox paniculata)
Those towering spikes of fragrant phlox blooms are summer garden stars, but they often finish the season looking less than stellar. September pruning addresses both aesthetic and health concerns for these zone 3-9 perennials.
Cut plants back to about six inches above ground level, paying special attention to removing any powdery mildew-affected foliage. Like bee balm, diseased phlox debris should be disposed of rather than composted to prevent disease carryover.
In regions where garden phlox grows natively, proper September pruning can sometimes encourage a modest second bloom period, though the main show will always be the summer display.
9. Herbaceous Clematis (Clematis integrifolia, C. heracleifolia, C. recta)
Wait – before you grab those pruners, make sure you know which type of clematis you’re growing! This is crucial because different clematis groups have completely different pruning requirements.
Only herbaceous (non-vining) clematis species benefit from September ground-level cutting. These include fragrant tube clematis (C. heracleifolia), solitary clematis (C. integrifolia), and ground clematis (C. recta). These perennial forms die back naturally each winter and respond well to fall cleanup.
All other clematis types – the popular large-flowered hybrids and spring bloomers – should be pruned according to their specific group requirements, typically after flowering or during dormancy. Pruning these varieties in September could eliminate next year’s flower display entirely.
10. Wormwood (Artemisia spp.)
The silvery, aromatic foliage of wormwood species adds wonderful texture contrast to perennial borders, and September pruning keeps these plants looking sharp through fall and winter.
Focus on removing dead, diseased, or damaged growth first, then lightly trim back green growing tips to encourage bushier growth. For woody species, avoid cutting into old wood, which may not regenerate reliably.
Those aromatic pruned stems shouldn’t go to waste – they’re perfect for fall wreaths and dried arrangements. The strong scent also makes them useful as natural moth deterrents in stored woolens.
One important note: if you’re dealing with invasive wormwood species that are crowding out native plants, feel free to be much more aggressive with your pruning efforts!
