Guide to Growing Dahlias in Your Garden

colorful dahlias growing in garden
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Guide to Growing Dahlias in Your Garden

A Gardener's Guide to Growing Dahlias

No summer garden is complete without dahlias!

Dahlias, genus Dahlia in the sunflower family Asteraceae, are a handsome group of garden flowers. Originally from South and Central America, today’s garden plants are mostly hybrids. You can find remarkable variety; from six-inch to six-foot plants, with flowers the size of quarters to eight inches across. Dahlias can be white, pink, red, yellow, orange, and combinations of those colors. The flowers can be single or double, with pointed petals (the cactus form), flat-petaled, very round (pompom dahlias) and many others. The foliage is usually a middle shade of green, but some varieties are coppery or black-purple.

Dahlias grow quickly from seed or established plants can be divided. Some of the finer varieties are not available as seeds. 

Dahlias flourish in full sun (except in the very hottest regions, where they benefit from partial shade in the afternoon). Plant them in rich soil. Provide abundant moisture but make sure the spot is well-drained. 

Planting for Success

Timing is Key: Plant your dahlia bulbs post-last frost, ensuring soil warmth for optimal growth. 
Location: Provide full sun exposure, while offering afternoon shade in hotter climates to prevent overheating. 
Soil Prep: Cultivate well-draining, nutrient-rich soil, incorporating compost to enhance fertility. 
Spacing Matters: Allow ample space between bulbs, promoting air circulation and unimpeded growth, typically 2-3 feet for larger varieties.

Use dahlias as big plants back against the fence or as a focal splash of color in a flower bed. Once they start blooming, they will flower until frost. Big varieties and older varieties will probably need to be staked to keep them from falling over. Dahlias can be very beautiful in containers, but be sure the container is large, especially if you are growing large varieties.   Make sure the soil is rich in nutrients and that the dahlias are regularly watered without being in a soaked soil. 

Plant dahlia tubers in your garden after all chance of frost has passed. Place them far enough apart that they don’t crowd each other. For example, for a large dahlia variety, at three feet apart they will grow into massive flower-covered herbs, while set a foot apart, the plants will merge by midsummer to create a wall of dahlias. Check the description of the variety. One of the joys of dahlias is that, since in most Zones you need to bring them in to protect them in the winter, unlike most plants, you can change the spacing next spring. 

Dig a hole about six inches deep. Mix compost and loose dirt into the hole so you can plant the tubers about three inches below the soil surface. Set the tubers with their eyes up. Cover the tubers with one to two inches of dirt. Unless your soil and climate are very dry, wait until the first sprout appears to water, then provide plenty of water. 

Caring for Your Dahlias

Water Wisely: Maintain consistent moisture levels, avoiding waterlogged conditions that are detrimental to root health. 
Support Them: Stake taller varieties to safeguard against wind damage, ensuring upright growth. 
Feed for Blooms: Apply a balanced, low-nitrogen fertilizer to stimulate vibrant blooms without excessive foliage. 
Pest and Disease Management: Vigilantly monitor for pests and diseases, employing organic or recommended treatments to safeguard your dahlias' health.

Dahlias are grown in all USDA climate zones, but are winter hardy only as far north as Zones 8 to 10. If their roots or rhizomes freeze, the plant will die. To carry-over dahlias between years, simply dig up the finger- or potato-like rhizomes and store them over the winter in a cool dry place. (See Overwintering Dahlias below.)

Enjoying the Blooms

Dahlias make terrific cut flowers, whether in bouquets or formal arrangements. Cutting encourages further blooming, too. You can affect the size of the flowers by pinching off buds; to make flowers larger, pinch off any side-buds; to make them smaller, remove the central flower bud. 

Overwintering Dahlias

In regions below zone 8, winter protection is essential. Post-first frost, unearth tubers, cleanse them, and store in a cool, dry location until the spring planting season.

Embrace the Beauty

Look at all the varieties and consider where you’ll plant them before choosing your dahlia. There are so many to choose from, you’re bound to find one for every area of your garden!