7 Beautiful Flowers You Can Sow in September – to Fill Your Garden With Color Next Year

September is an ideal time to start creating stunning displays for next spring and summer. Even though this season isn’t over, sowing hardy annuals and perennials this month sees them put down strong roots before winter and reward you with earlier blooms next year.

A wide variety of hardy annual and perennial flowers can be sown in September to ensure your flower beds, borders, and containers are flooded with gorgeous color and texture. Hugely popular plants like sweet peas, lupines, larkspur, coneflower, and columbine are among some of the best flowers to plant in September.

Let’s take a look at seven great flowers to sow in September. Some can be sown directly outdoors, and others are best started indoors – for them, get yourself some pots and a bag of quality potting compost (like this organic seed starting mix from Burpee) so you can spend some quality time sowing flower seeds over the coming weeks. It’ll be hugely rewarding to see those seeds germinate and follow their adventure as they develop and burst into bloom next year.

1. Sweet Peas

Sweet peas are the most quintessential cottage garden plants, but I also think they are essential for anyone with a cut flower garden. With so many sweet pea varieties out there to choose from – there are reputedly over 1,000 cultivars and varieties in existence – there will be one to suit your style.

Many gardeners routinely start growing sweet peas in late winter or early spring, but sowing seeds in mid to late September is a great way to get ahead. It is something we always did when I worked in public gardens, for an earlier display, and you can get the longest show by doing sowings in both fall and spring.

If you sow this month, the seeds will germinate, then go dormant in winter, and burst into life in spring for earlier displays of fragrant flowers. To guarantee they survive, overwinter the young sweet peas in an unheated frost-free greenhouse or cold frame to plant them out in spring.

When you plant sweet pea seeds this month, use deep pots or root trainers (you can get deep root trainers at Amazon), as they develop strong roots quickly. You can soak the seeds before sowing; it breaks the tough outer shell and speeds up germination.

If you adore highly fragrant sweet peas, these Perfume Delight sweet pea seeds from Botanical Interests are right up your street. The mix will produce purple, red, rose, scarlet, white, and blue flowers, all with a glorious scent.

2. Larkspur

Larkspur is among the top hardy annuals you can sow directly outdoors in September. Along with the likes of bachelor’s button, nigella, and California poppies, sowing hardy annual flowers gives you earlier blooms next summer, and they can all be quickly sown directly into the garden.

Larkspur is a great plant for adding color and height to beds and containers. The flower spikes (which are also popular for cut flowers) come in lots of colors and, once they are growing in a garden, will self-seed and pop up year after year.

To grow larkspur from seed, sow the seeds around a quarter-inch deep – they only want to be covered lightly – and keep the seed bed moist.

Larkspur seedlings are somewhat erratic, and I have had mixed success with them. However, be patient and give them time to emerge rather than getting frustrated. Some can be slower than others, but they do often appear in the end.

Thin the seedlings as they develop to eight inches apart, and you can carefully lift and transplant the surplus seedlings rather than throwing them away.

For truly show-stopping larkspur, this Giant Imperial Mixture of larkspur seeds from True Leaf Market produces tall spikes in shades of blues, purples, pinks, and whites that are great for cutting.

3. Coneflower

Coneflowers, or echinacea, may still be in full glory this month. Enjoy the show, but let it encourage you to want more. Sowing coneflower seeds in September means you get even more dazzling color next summer.

If you are already growing coneflowers, why not grow more?. There are so many coneflower varieties out there that you’ll find one that complements your existing plants. The large, nectar-rich flowers are stunning in full bloom and great for pollinators – so go on, add a few more to next year’s flower beds.

Sow coneflower seeds towards the end of September directly into your beds and take advantage of the natural winter cold needed to break their dormancy. The seeds require a period of cold stratification to germinate, and sowing outdoors ahead of the frosts ensures they get that treatment without the hassle of refrigerating seeds before sowing indoors.

Pick a sunny spot, weed the bed, and rake it level. Gently scatter the coneflower seeds, or sow in shallow rows, and cover them lightly with some sieved soil or compost. Water the seeds gently and keep a close eye on them to keep the soil moist.

Purple coneflowers are one of the best low-maintenance perennials for pollinators. You can get a pack of purple coneflower seeds at Amazon.

4. Columbine

Columbine, or Aquilegia, is a charming native spring flower you can plant to attract pollinators and hummingbirds. With delicate blooms in colors such as red, blue, yellow, white, and more in spring and early summer, it adds color and texture to the garden, and the short-lived perennial will self-seed readily once established.

You can sow columbine seeds directly outdoors in September. Pick a sunny spot and ensure that the soil is well-draining. The key to success with columbine seeds is pressing them into the soil but not covering them, as light is essential for germination.

Sowing outdoors this month will give the seeds natural stratification during the winter months. However, columbine seeds require patience. It should take around 30 days in early to mid-spring, after the temperatures warm, for the seedlings to appear, but some may take up to 90 days.

For a pretty mix of early spring flowers, these ‘Harlequin Mixed Colors’ columbine seeds from Burpee have flowers in pure white, yellows, pinks, blues, purples, and some bicolors.

5. Lupine

Lupines are native plants adored for bringing bold spikes of color to a space in late spring to midsummer. The bright blooms add height and drama. Once they fade, you can even encourage a second flush by deadheading lupines and removing the spent flower stalks.

You can start growing lupines in late September, and this method comes with two advantages. One is, like others on this list, it provides a natural period of cold to break dormancy.

The other is that lupines have strong taproots, which means they need to be sown directly rather than started indoors, pricked out, and potted up. If you disturb the taproot, the lupine won’t thrive.

Scarifying seeds by making a small nick on the surface helps with germination. This can be done with a pair of nail clippers, a sharp knife, or by rubbing the seed coating with sandpaper or a file, like this tough steel file at Walmart.

Sow the lupine seeds at least six inches apart and cover with a small amount of soil. The seedlings will appear in spring, but may not burst into bloom until their second year.

If you only have smaller beds or containers for lupines, these ‘Pixie Delight’ lupine seeds from Botanical Interests are ideal, as the plants grow only 12-18 inches tall yet produce impressive spikes in shades of pink, purple, blue, and white.

6. Eryngium

Eryngium, also commonly known as sea holly, has distinctive, spiky flower heads that mainly come in shades of blue, but also silvery green or white. Any eryngium variety is guaranteed to bring drama and architectural interest to any bed thanks to its flowers, tall stems, and spiny foliage.

To sing its praises more, eryngium is a drought-tolerant perennial that can stand up to hot, dry periods in summer.

If you want to grow eryngium, and why wouldn’t you after hearing all that above, it is another flower that prefers to be sown directly, as its roots are easily disturbed when transplanted. You can sow seeds indoors, but then you need to be careful when transplanting them outside.

To make life simpler, stick to sowing directly into a sunny growing position with well-draining soil. Press the seeds into the soil but don’t bury them too deep, as they need light for good germination.

You can get silver blue sea holly seeds at Amazon to sow in fall or spring.

7. Scabiosa

Scabiosa, or the pincushion flower, looks like its common name suggests. The delicate pincushion-like blooms sit on tall stems, bobbing in the breeze and attracting lots of pollinators during summer.

Scabiosa can be annual or biennial flowers and come in shades of pink, dark red, and white. Once the flowers go over, scabiosa becomes one of the best plants for seedheads, with the bristly globe-shaped pods not only looking stunning but having potential for dried flower displays.

You can start growing scabiosa indoors or outdoors in September. Either sow seeds onto the surface of trays, modules or small pots (get biodegradable plant pots at Burpee to reduce transplant shock) filled with seed compost and cover with a thin layer of more soil or vermiculite (get bags of vermiculite at Amazon).

Or press the seeds into the soil into their intended growing positions and again give them a light covering.

This HiGro Mix of scabiosa seeds from True Leaf Market is great for long-stemmed flowers in a variety of pastel shades for cutting.

As fall dawns, many gardeners' thoughts turn to cutting back borders and neatening the garden ahead of winter. However, you don’t want to prune everything in the coming weeks, for good reason. There are perennials you should not cut back in fall, such as black-eyed Susan, coneflowers, milkweed, and globe thistle, as they provide food and shelter for pollinators and birds over the colder months.

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