13 Annual Flower Seeds to Plant in September

If you live in a warm climate, sowing seeds in late summer and early fall brings sweet pleasure as the seasons transition. In cold climates, sow selections to nurture over the winter for planting out in spring. These will get a jump start on flowering with sturdy stems and leafy growth.

Direct sowing at this time of year involves annuals with a quick turnaround in warm climates for a late fall or winter show. In colder regions, seeds overwinter for spring emergence. Plant frost-tolerant annual flower seeds in September to see what emerges for a spring surprise. Or, use seed trays and pot up seedlings in the cold months for transplanting as the weather warms.

When sowing seeds, use the “days to maturity” indicator to ensure time to enjoy the flowering phase before freezing. If frost is near, delay planting until after a few cold snaps to avoid germination and damage to new seedlings. If you use a crop cover, tunnel, or hoop system, the options for sowing hardy annuals increase. For starting flower seeds indoors in September, keep the annual seedlings protected from winter extremes in a sheltered space like a cold frame, greenhouse, shed, or garage with a window.

Certain flowers specialize in bridging warm and cool seasons with a profusion of color. They delight in cool fall and spring conditions and extend both flowering seasons.

Bachelor’s Button

Blue Boy Bachelor’s Button Seeds

Zeolights Calendula

Zeolights Calendula (Pot Marigold) Seeds

Black Velvet Nasturtium

Black Velvet Nasturtium Seeds

Calendula

Calendula is a quick-grower with yellow, orange, pink, and bicolor daisy-ray flowers. Its single or double blooms bring warmth to chilly days and have an extended bloom time.

Calendula grows best in fall and spring. In warm climates, it performs over the winter. The flowers emerge from spring through frost in cool climates, taking a break in high summer heat.

Calendula is an annual grows easily from seeds, with flower buds opening about 30 days after an early September sowing. Its leaves and flowers are edible and make a beautiful dried or fresh floral addition. Plants may self-sow for a spring bloom.

Love-in-a-Mist

Love-in-a-mist is a nostalgic bloomer with delicate, feathery foliage and airy flowers surrounded by “misty” bracts. Petals are deeply cut in shades of blue, rose, white, and lavender. Green and burgundy balloon-shaped seed pods extend interest post-bloom. Both the blooms and pods are showy in floral arrangements.

Nigella performs best as a fall or spring annual and wilts in hot conditions. Sow seeds in late summer or fall for seedlings to overwinter. They’ll establish sturdy root systems for more prominent, earlier-flowering plants in the spring. Direct sow or use biodegradable pots to avoid disturbing taproots during transplanting.

Love-in-a-mist spreads readily via self-seeding. Prevent unwanted spread by deadheading spent blooms and removing seed pods before they drop.

Sweet Peas

Ornamental sweet peas enchant with fragrant, colorful blooms on twining vines. Sweet peas are popular springtime growers but perform beautifully in autumn when the sweet perfume is a surprise. Petals are pink, mauve, red, blue, peach, and white. Opt for ‘Beaujolais’ for a rich wine-colored autumnal variety.

The frost-tolerant beauties grow quickly from seed. Direct sow them or transplant potted seedlings to enjoy before heavy frost. Ideal growing temperatures are between 55 and 65°F (13-18°C).

Sweet peas cling and climb; for best growth, they need a support structure like a tripod or trellis. Use them as a container focal point for vertical interest. Dwarf varieties quickly reach two to three feet and don’t require support.

Nasturtium

Nasturtium flourishes the mild temperatures of fall, making it a good fit for harvest-themed plantings and loose, natural, edible compositions. It also grows as a houseplant year-round. Sow these annual flower seeds indoors in September and enjoy a brightened up the winter kitchen.

A late summer round of bright blooms draws pollinators until freezing temperatures. Nasturtium grows quickly from seed but won’t withstand a heavy frost.

Nasturtiums are easy to grow in beds, hanging baskets, window boxes, and containers. The edible round leaves and large tubular flowers make a lovely garnish for autumnal salads and platters.

Scarlet Flax

Flax is a showy blooming plant grown for its edible seeds, oils, and flowers. These easy-care, low-maintenance growers tolerate heat, humidity, and cool weather.

‘Scarlet’ is an eye-catching annual variety with a profusion of red flowers that grows easily from seed and attracts many pollinators in late September and October when they need the nectar. While the seeds aren’t edible, it’s an easy bloomer between seasons. Without deadheading, ‘Scarlet’ self-seeds for recurrent color.

Direct sow ‘Scarlet’ flax by scattering seeds on moist soil and gently tamping for soil contact. The seeds need good light exposure to germinate, so don’t worry about covering them. Plant them in late summer for fall color.

Cornflower

Annual cornflowers, also known as bachelor’s buttons, have rich blue ruffled flowers that flush in late spring and early summer with a light repeat bloom in fall. A late summer sowing yields fall flowers in warm regions or spring color in colder growing areas. In warm gardens, it blooms through winter. 

Cornflower has tall, upright stems. The blossoms attract butterflies and birds enjoy the seeds. However, in optimal conditions, especially in northern climates, cornflower reseeds aggressively and can become invasive. 

Deadhead blooms to prevent seeding. Asters, fleabane, and penstemon offer native alternatives to the carefree cornflower. These perennial selections have cultivars in shades of violet and blue.

Snapdragon

Snapdragons brim with vintage appeal and showstopping plumes in saturated hues. They make beautiful cut flowers and, in moderate climates, survive winter temperatures in the garden or containers for a long-lasting display. 

In mild climates, snaps bloom from autumn through spring. In colder climates, they flower in spring, summer, and fall.

Snapdragons take 60 to 80 days to mature from seed. Opt for nursery starts in short growing seasons. In late summer, start seeds indoors in hot climates. They flower almost year-round in mild conditions. 

Once established, snapdragons tolerate subfreezing temperatures. Keep them evenly watered to survive freezing. Plants are hardy to 25°F (-4°C) and perhaps lower with mulch and protection.

Violas & Pansies

Pansies and violas are hardy annuals with cheery “faces” that bloom nonstop for front-of-the-border color. Tuck them into pots for a profusion of petite flowers.

They survive winter in mild climates and withstand seasonal transitions in colder climates. In northern climates, grow them for a fall or spring display. Like snapdragons, pansies and violas flower reliability in chilly temperatures and withstand frost. 

These tough annuals tolerate cold spells with temperatures in the 20s°F (-7°C) and sometimes lower. Pansies and violas are easy to grow in well-draining soils. They benefit from deadheading to promote more blooms (pansies, especially). Pinching old blooms channels energy from seed production into further flowering.

Poppies

Poppies cheer the display with colorful, tissuey petals and contrasting centers that wave or rise tall in the landscape. Poppies prefer cool weather and go dormant or die back in the heat of summer. They grow as annuals with late winter and early spring color. Direct sow them in the fall to germinate and flower in the spring.

P. rhoeas (Flanders or corn poppy), P. nudicale (Iceland poppy), and P. orientale (Oriental poppy) are popular species with a range of colors. The ‘Champagne Mix’ Iceland poppy and ‘Mother of Pearl’ corn poppy bring lovely pastel and sherbet shades with papery blooms on wiry stems. Oriental poppies in crimson and scarlet (among other shades) with dark centers bear large flowers for a sweep of color en masse.

Poppies are easy to grow and low maintenance in moderate temperatures. Deadhead faded blooms to prevent reseeding.

Foxglove

Foxgloves are technically cold-hardy biennials, but we’re including them here because they’re too pretty to miss. They bloom in spring and summer in cool climates and establish over the winter in warm regions for a late spring bloom display. 

Foxgloves produce loads of bell flowers that crowd tall, sturdy stems. Colors range from purple to rose to creamy white. Pollinators find them irresistible, especially early in the season before other springtime flowers appear.

In mild climates, surface-sow Digitalis seeds in late summer and early fall. Foxgloves grow best in consistently moist, organically rich soils with good drainage.

Sweet Alyssum

Sweet alyssum is a small annual with seemingly endless blooms. In cool seasons, its profusion of white, pink, or purple pincushion flowers covers the mounding foliage. Its sweet fragrance attracts pollinators and other beneficial insects.

The delicate-looking annuals are tough and hardy down to 20°F (-7°C). Seedlings emerge in 5 to 15 days. Sweet alyssum self-seeds and volunteer seedlings may pop up in the spring. 

In the heat of summer, plants turn yellow and fade but resume blooming with cooler temperatures. They’ll die out in southern climates but recover in northern growing regions. Treat them as cool-season annuals for spring and fall in hot, southern zones.

Crimson Clover

Crimson clover provides a valuable service as a cool-season crop cover. Cover crops are easy to sow and improve growing conditions if you have bare earth to hold until spring. The specialized plants improve and nourish the site. Cover crops help with weed suppression, erosion control, compaction, and increased soil nutrients.

Scatter crimson clover seeds evenly and generously. Enjoy the fall and winter greens with minimal maintenance, only watering during dry spells. These upright growers have a taproot that fixes nitrogen. One-inch-long red flowers appear in spring and attract beneficial insects.

Cut them back before they go to seed, leaving the cut material in place or adding it to the compost pile. Use them in raised beds for soil improvement during quiet times.

This frost-tolerant ground cover is hardy to -10°F (-23°C). It grows over the winter as a cool-season annual in zones 6 and warmer. Sow seeds six to eight weeks before the first frost date.

False Queen Anne’s Lace

Ammi isn’t invasive like its Queen Anne’s Lace relative but produces similar domed umbel blooms with sprays of white florets. False Queen Anne’s Lace adds airy appeal as a lovely border filler and fresh cut or dried arrangement. This annual performer received the Royal Horticultural Society’s Award of Garden Merit.

Look to ‘Dara’ for a mauve, burgundy, and crystal pink shimmer. The tall stems reach three to four feet tall on well-branched, slender stems.

Typically sown pre-frost in the spring, a fall crop can be sown indoors or directly sown outdoors for a jumpstart on spring flowering. Once established, Ammi is relatively drought tolerant, though it flowers best with regular moisture. Deadhead spent blooms for faster reflowering and to prevent self-seeding.