Though we tend to think of September as an autumn month, most of its days are technically in the summer. Temperatures are warm but not hot, and you’re not likely to see a frost until October, making it an ideal time for gardening. So why is it so hard to find colorful flowers this month?
The key to September color is planning ahead. Dahlias are the perfect solution. These tender tubers generally bloom about two months after planting, so you can time the floral show for early to mid-September by waiting until July to plant them. These flowers have been bred to bloom in all sizes and with shapes that include spiky, pincushion and more daisy-like petals.
Dahlia Basics
Growing Zones: Dahlias can be planted in zones 2-11, but they will only survive the winter in zones 8-11. Kansas City gardeners will need to lift the roots and store them for the winter.
Bloom Time: Spiky, mum-like blooms appear about 8 weeks after planting outdoors for the season.
Exposure: Full sun
Mature Size: 2 to 5 feet tall with a spread of 2 to 3 feet, depending on variety
Notes: Dahlias are technically biennials, but Kansas City gardeners can treat them either as annuals or as tender perennials. They come in an extremely wide range of shapes, sizes and colors, including white, cream, yellow, orange, bronze, pink, red and purple. Dahlias are easy to grow and often inspire collectors thanks to the many varieties available.
Growing Dahlias in the Landscape
Choose a sunny location for dahlias, which need six to eight hours of sunlight per day for best bloom. It’s also a good idea to choose a spot sheltered from prevailing winds if possible. Dahlias prefer average to fertile soil that drains well.
Planting Dahlias
Dahlias are grown from tubers, which are brown, fleshy roots. To plant them, dig a hole about 6 to 8 inches deep and big enough around to hold the tubers without crowding. Add a handful of compost or bone meal to the planting hole before placing the plant inside, tubers down and stem up. Cover with an inch or two of soil and do not water. Space plants about 2 feet apart.
In a week or two, the Dahlias will sprout and send out green shoots. At this point they can be watered, and you can add soil to the hole to support the stems as they grow, stopping when the holes are completely filled in. Do not mulch, as this can encourage rotting and insects.
For Dahlias with large flower heads or tall stems, place stakes next to plants before covering them with soil. It will be crucial to tie stems to the stakes as plants grow to keep them from toppling over or breaking in the wind. Staking at planting time will keep you from accidentally piercing the tubers once they’re covered by soil.
Ongoing Care for Dahlias
Once your dahlias are about 10 inches tall, you can apply a balanced fertilizer every two to three weeks throughout the growing season. When Dahlias reach a foot in height and have at least four sets of mature leaves on the center stem, pinch the center stem back to the newest leaves for a bushier plant.
To save Dahlias for the next growing season, wait until frost kills the foliage and cut plants back to about 4 inches in height. A week later, gently dig up tubers and allow them to air dry in a frost-free, dark place. Trim stems back to 1 inch and pack tubers in pots filled with sand or vermiculite. You can layer them, but make sure each is separated by a layer of sand. Store in a cool, dark place that won’t get colder than 40 degrees in the winter, and you’ll be able to plant them again next summer.