11 Hardy Annual Flowers You Can Plant in September

September marks the end of summer and the beginning of autumn. Leaves begin changing their colors, night temperatures are dropping, and rainfall is returning. It’s a beautiful time in the garden. 

As the weather changes, you’ll notice your heat-loving plants begin to decline. Some tucker out completely, while others suffer a slow death until the first frost. Don’t let them take up space! Instead, remove them and plant hardy annual flowers in September.

These prolific bloomers will fill the yard with color, structure, and texture. They’re ideal in cold and mild climates, as they’ll often overwinter in mild ones!

Black Magic Bachelor’s Button

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Black Magic Bachelor’s Button Seeds

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Zeolights Calendula

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Lacy Phacelia Cover Crop

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Lacy Phacelia Cover Crop Seeds

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Bachelor’s Button ‘Black Magic’

	botanical name Centaurea cyanus ‘Black Magic’
	sun requirements Full sun
	height 20-24”
	hardiness zones 2-11

Bachelor’s button earns its name because the flowers resemble buttons on a coat. They’re frilly, lacy, and they come in a range of colors. One of the best is ‘Black Magic,’ a black-purple hued cultivar.

‘Black Magic’ doesn’t grow too tall; it stays under two feet, and it doesn’t require staking to stand upright. Sow seeds a quarter inch deep, and keep them moist while they sprout. They’ll bloom in winter in mild regions, and in spring in cold ones, a perfect hardy annual flower for September. Keep these in containers where they tend to invade natural areas.

Calendula ‘Resina’

	botanical name Calendula officinalis ‘Resina’
	sun requirements Full sun
	height 2’
	hardiness zones 2-11

Calendula is surprisingly frost-tolerant despite its tender appearance. It sports orange, peach, or yellow blooms and strappy green leaves on short-growing stems. Many cultivars exist to choose from if you’re planting hardy annual flowers in September. There are single and double types, as well as large or dwarf varieties. 

Try ‘Resina’ if you want to eat the edible petals of the calendula blooms. They go well in fresh dishes like salads, sandwiches, and charcuterie boards. ‘Resina’ is best for culinary purposes, as its petals contain more resin and flavor than other types.

If you’re having trouble finding calendula, try searching for its other name, pot marigold. Sow seeds this September for midwinter blooms in mild regions.

Calendula ‘Zeolights’

	botanical name Calendula officinalis ‘Zeolights’
	sun requirements Full sun
	height 1-2’
	hardiness zones 2-11

‘Zeolights’ is unlike any other calendula. Its blooms have many rows of petals that sprout orange-bronze and unfurl to a light pink. They’re truly stunning! ‘Zeolights’ deserves its own bed apart from other calendulas. 

In the garden, this calendula stays between one and two feet tall. Plant these hardy annual flowers in September in front of tall perennials and shrubs to fill your borders with color. When the petals unfurl, you may pick them for a fresh addition to your meals. 

Forget-Me-Not ‘Victoria Blue’

	botanical name Myosotis sylvatica ‘Victoria Blue’
	sun requirements Full sun to partial shade
	height 6-8”
	hardiness zones 3-8

It’s hard not to think about Patrice Rushen when planting forget-me-nots! These flowers are in the song of the same name, with this characteristic chorus: 

Sending you forget-me-nots

To help you to remember

Baby, please forget me not

I want you to remember

And you will remember forget-me-nots! These flowers are gorgeous, easy-growing, and beautiful during the cold months. Bright blue blooms emerge from short stems. They open much earlier than most other annual flowers.

Forget-me-nots may survive the winter, though they act like annuals in most areas. Take care when planting them in the garden, as they may naturalize and escape cultivation. Mow them after they finish blooming to prevent reseeding, or snuff them out with a thick layer of mulch.

Forget-Me-Not ‘Victoria Pink’

	botanical name Myosotis sylvatica ‘Victoria Pink’
	sun requirements Full sun to partial shade
	height 6-8”
	hardiness zones 3-8

‘Victoria Pink’ is another forget-me-not that fills the yard with cheery blooms. It’s just like ‘Victoria Blue’ except for its bloom color. This variety erupts into bloom with dainty flowers that sport light pink hues. 

Grow the two forget-me-not cultivars together for a pastel mix of green, pink, and blue. Or, opt for ‘Victoria Pink’ and plant it en masse for an explosion of color.

These flowers may not appear until late winter or early spring next year. Plant these hardy annual flowers in September to ensure they sprout in time for the season. 

Lacy Phacelia

	botanical name Phacelia tanacetifolia
	sun requirements Full sun
	height 1-3’
	hardiness zones 2-11

Lacy phacelia is a multi-purpose native plant with exceptional cold-tolerance! It’s a hardy annual that grows wild from California north through the Pacific Northwest. It features purple blooms, lacy foliage, and an abundance of seeds.

Many growers plant lacy phacelia in September to use it as a cover crop in the vegetable garden. Others use it in the warm months as a wildflower. Its self-seeding tendencies make it an excellent choice for wild plantings and open spaces. 

Leave this phacelia to overwinter after the bloom period is over. The dead plant matter will cover the soil to act like mulch. It’ll protect and insulate it, and you’ll have rich, fertile soil by spring. 

Lupine ‘Pixie Delight’

	botanical name Lupinus mexicanus ‘Pixie Delight’
	sun requirements Full sun
	height 12-18”
	hardiness zones 2-11

There are annual, biennial, and perennial lupines, though ‘Pixie Delight’ is a cold-hardy annual variety that thrives in home gardens. It’s shorter than other cultivars, as it stays under two feet tall. 

This lupine features squat spikes of flowers early in the growing season. They come in shades of pink, blue, purple, and white.

Sow seeds of these hardy annual flowers in September for flowers the following year. Lupine seeds need some time outdoors in the cold before they’re ready to sprout. 

Pansy ‘Swiss Giants Blend’

	botanical name Viola x wittrockiana ‘Swiss Giants Blend’
	sun requirements Full sun to partial shade
	height 6-9”
	hardiness zones 6-10

Pansies are iconic flowers for September! You’ll see them filling the shelves of your local nurseries and garden centers when the weather cools in autumn. Many new types come out annually, and there are dozens of heirloom favorites to choose from.

‘Swiss Giants Blend’ has a mix of many. It’s the perfect seed packet to buy if you can’t decide on a single pansy. You’ll find red, yellow, white, purple, and pink blooming pansies inside the mix. 

Pansies are frost-tolerant perennials that may survive for a year or two if they’re kept moist. If not, they tend to die in summer as the ground dries and the heat grows more abundant. Plant these hardy annual flowers in September for flowers during the cold months, then replace them with warm-loving plants in spring.  

Viola ‘Cool Summer Breeze’

	botanical name Viola cornuta ‘Cool Summer Breeze’
	sun requirements Full sun to partial shade
	height 8”
	hardiness zones 6-9

All pansies are violas, but not all violas are pansies. The Viola genus comprises hundreds of annual and perennial species that fill woodlands, roadsides, and gardens with charm. Many are native to the U.S., like the evergreen violet of the Pacific Northwest. 

‘Cool Summer Breeze’ is a blend of violas with small flowers in various colors. They’re multicolored; they have blooms with white-yellow, purple-white, and all purple petals. Dainty and charming, this batch of violas will impress garden onlookers from September through spring. 

Unlike pansies, these violas often survive year to year. They benefit from afternoon shade in the hot months, and they require consistent moisture year-round to thrive. 

Sweet Pea ‘Little Sweetheart’

	botanical name Lathyrus odoratus ‘Little Sweetheart’
	sun requirements Full sun to partial shade
	height 8-14”
	hardiness zones 2-10

Sweet peas round out our list of hardy annual flowers for September in style. They’re lovely and enchanting, with pea flowers and vining tendril-like stems. Grow them in baskets and let them hang over the sides, or set them on a trellis and let them climb it. 

Out of all the sweet peas, ‘Little Sweetheart’ works the best in containers and planters. It’s a dwarf variety with petite flowers that emerge all over the stems. Plant its seeds during September, and the flowers will blossom in early spring. 

Sweet Pea ‘Mammoth Navy Blue’

	botanical name Lathyrus odoratus ‘Mammoth Navy Blue’
	sun requirements Full sun to partial shade
	height 5-6’
	hardiness zones 2-10

‘Mammoth Navy Blue’ excels where ‘Little Sweetheart’ fails. It’s an annual sweet pea variety with giant blooms on long vining stems. They may reach up to six feet long. The blooms are a rich navy blue color that stands out in the landscape.