What perennials can I plant in September? 7 of the best to get in the ground before cold weather arrives

Wondering what perennials to plant in September? This is a great month to add color and texture to your garden and ensure it blooms well for the next few years. From the vibrant yellow flowers of Black-Eyed Susan to the whimsical plumes of ornamental grasses, there are a lot of options to look at. 

'September is a great month to get planting as temperatures fluctuate from warm to slightly chilly making it the perfect opportunity to get plants in the ground before winter kicks in,' says Chris Bonnett, founder of Gardening Express.

If you're ready to get your backyard in shape, consider these perennials suggested by experts. 

1. Anemone 

'My two favorite fall-blooming anemones are Anemone 'Honorine Jobert' with pearlescent white flowers and Anemone robustissima which has light pink blossoms,' says Kat Aul Cervoni, landscape designer and founder of Staghorn NYC and The Cultivation by Kat. 'These late-summer/autumn-blooming flowers typically reach between 3-4’ ft so are great in the middle to back of the border, but because of their tidy basal foliage growth, can also look lovely at the front edge of a border as well. Just note that because their stems are so tall and thin, they can occasionally flop over, so some staking or supports might be helpful.'  

Add these to your modern garden but remember that these anemones require full sun, but also do very well in partial shade and prefer moist soil conditions. These plants are not particularly drought-tolerant and also do not like standing water. 'Once established, these can be aggressive spreaders, so be mindful especially in smaller gardens,' says Kat.

2. Salvia nemerosa Caraddonna

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A good option for urban gardening is the Salvia nemorosa 'Caradonna', also called Balkan Clary. 'Perfect for sun or dappled shade, stunning spires of blue-violet flowers appear in early and mid-summer if planted now,' says Chris Bonnett from Gardening Express.

The leaves of this plant have a light grey color and a pleasant scent. If you're up for cultivating this variety, you'll have to ensure you have well-draining soil such as loam, chalk, or sand. They do not do well on clay unless it has been improved with lots of organic matter to help drainage. For its maintenance, you need a handful or two of fish, blood and bone fertilizer in spring. 

3. Cimicifuga (Bugbane) 

Amongst the  best flowers to plant in September is Cimicifuga. 'Cimicifuga (aka Actaea) comes in several varieties with deep purple/bronze foliage that’s perfect for adding late-season interest to your part shade/shade border,' says Kat. 'My go-tos are Cimicifuga 'Brunette' for white flowers and Cimicifuga 'Pink Spike' for pink flowers. These hardy perennials sport lacey, deeply colored foliage that adds dimension to the garden bed throughout the summer then produces fragrant, towering spikes of small white or pink flowers in late summer/fall.'

'These look beautiful throughout the garden border, from the front to the back, but note that they can be slow to establish, so may need a few seasons before they thicken up,' says Kat. 'Cimicifuga does best in part-to-full shade areas with consistent moisture. They are prone to leaf scorch if placed in too much sun or allowed to dry out.'

4. Echinacea ‘White Swan’

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To add elegance to your garden, consider Echinacea purpurea ‘White Swan’ which is a compact seed-grown perennial cultivar. This is one of the best heat-tolerant perennials and thrives in the most sunny sites due to its strong stems and deep roots. These have prominent golden cones with creamy white reflexed rays. 

'A rarer version of the popular purple coneflower, Echinacea ‘White Swan’ are wonderful when planted in drafts and will attract insects to your garden next summer,' says Chris.

The ideal location for it is in full sun with fertile, well-drained soil. This is pest-resistant and unpalatable to deer and other herbivores.

5. Aster

Add myriad colors and heights to your courtyard garden with Aster (or Symphyotrichum). 'This easy-going perennial with daisy-like flowers has a variety that works for almost every garden,' says Kat. 'For a sunny, dry garden, try Aster 'October Skies' which has gorgeous sky blue flowers topping out at 12”-18” high; perfect for late-season color at the front of the border. Aster 'Avondale' has clouds of light blue flowers that rise to 2’-3’ high by September. This one tolerates part shade and adds lovely fall color to the edge of a woodland garden.' 

'For a massive and vibrant burst of late-season color, opt for Aster novae-angliae (New England Aster), which reaches 4’-6’ in height with deep pinkish-purple flowers atop robust stems,' says Kat. 'These love full sun but can take part-shade. Asters are a magnet for pollinators and are an important food source for various species late in the season.'

6. Euphorbia ‘Miners Merlot’

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Enhance your porch, backyard, or terrace garden with Euphorbia ‘Miners Merlot’. This perennial grows in an upright rounded mound 18 to 24 inches tall and equally as wide and is ideal for use as an accent or in groupings in garden beds and containers.

'Bright acid-yellow flowers mounted on deep burgundy stems mean this perennial will be a star of your garden next summer if planted in September,' says Chris.

It is heat and drought-tolerant, so perfect for a xeriscape or rock garden, but is also deer-resistant, so it's nice in any bed or border and even in containers.

7. Anemone ‘Pink Cloud’

If you're wondering how to plan a modern garden that looks eye-catching and lush, a good perennial to add to the landscape is Anemone ‘Pink Cloud’. This large, prolific, single pink blossoming variety is more compact than a typical Japanese Anemone, with no growth regulators required. Apart from planting in the garden, these are a great choice for pots or small gardens, too.

'Flowering from late summer through to fall, this stunning perennial will be the envy of your friends,' says Chris. 'They’re tolerant of shade, which is why we advise planting them now for a great show next year.'

These prefer a semi-shaded environment, and well-drained soil which is rich in organic matter.