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How to Grow: Dahlias
Learn about dahlias, including how to plant and grow them.
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How to Grow: Dahlias
full sun, part sun
Bloom Period and Seasonal Color
late summer into fall in colors such as pink, salmon, white, cream, red, and bi-colors
Mature Height x Spread
1 to 5 feet x 1 to 3 feet
attract beneficials, attracts hummingbirds, deer resistant
If you’re looking for a big showy flower to cap off the end of the growing season and continue blooming into fall, consider the dahlias. Dahlia plants can reach up to 5 feet tall and 3 feet wide making a statement with their dark green or burgundy colored foliage. The real show happens in late summer when the flowers appear. There are more than 20 different dahlia flower shapes with the most common the pom-pom, water lily, cactus, and decorative. Some are literally the size of dinner plates. That’s one big flower! There are single and double flowers available in a wide range of colors. The flowers attract butterflies and hummingbirds, are great for cutting and flower arranging, and are not favored by deer.
Where, When and How to Plant
Dahlias are not hardy in our region and should be treated as an annual or the tubers should be dug and stored indoors in winter. Plant dahlia tubers in spring once the soil temperature is above 60F, about the time you’d plant corn. Plant bulbs in well-drained, compost-amended soil. Place a handful of an organic fertilizer in the hole. You can also plant in containers indoors, 4 weeks before your last frost date. Space plants 2 to 3 feet apart.
Support tall varieties and large-flowered varieties with a cage or stake to keep the blossoms from flopping over. Apply additional organic fertilizer monthly as a side dressing. Mulch with bark mulch to control weeds and keep the soil evenly moist.
Regional Advice and Care
Control slugs and snails on young plants by setting out beer traps, sprinkling organic iron phosphate baits and wrapping copper flashing around containers. To store, dig tubers in fall after frost has blackened the foliage. Cut the foliage to the ground, lift the tubers and knock off excess soil. Let the tubers dry in a warm, airy location out of direct sun for one week and then store in a perforated, plastic bags filled with slightly moistened peat moss in a cool basement.
Companion Planting and Design
Plant tall dahlia varieties in the back of a perennial flower border among other fall bloomers, such as anemones. hardy hibiscus and ornamental grasses. Plant shorter varieties in containers or in the front of the garden. Consider planting them en mass for an amazing, wow effect in late summer.
‘Bishop of York’ stands 4 feet tall with single golden blossoms on dark colored foliage. ‘All That Jazz’ has rose-red, zinnia-like, 5-inch diameter flowers on 4-foot tall plants. ‘Envy’ has amazing 11-inch diameter red blooms on 3-foot tall plants. ‘Frank Holmes’ has small pompom-shaped, lavender colored flowers on 3-foot tall plants. ‘Inflammation’ has single apricot-colored flowers on 18-inch tall plants. ‘White Lightning’ is a white, cactus-shaped variety on 4-foot tall plants that’s good for cutting.
Excerpted from my book, New England Getting Started Garden Guide.
There are few perennials that flower in fall, but dahlias are the darlings of autumn. These Mexican natives produce one to six-foot tall plants depending on the variety. The flowers can be as diminutive as a button or as large as a dinner plate with colors such as white, pink, red, yellow, and lavender. They’re grouped by flower shape, with cactus, water-lily, and pom-pom being some of the more unusual types.
Dahlias grow best in full sun on warm, fertile, well-drained soil. They take the whole growing season to flower, but once they start, the show is magnificent and lasts till frost. Stake or cage large plants or plants with large flowers to keep them from falling over. Pick them in the morning, place the stem in 2 inches of very hot water and allow it to cool for an hour. They’ll last for up to one week.
Dahlias are not hardy in our climate, so once frost has blackened the tops, cut back the plants to the ground. One week later, dig up the tubers, clean off the soil, and store in a dark, cool basement in slightly moistened sand or peat moss.
Now for this week’s tip: Off with their heads! – the Brussels sprouts heads that is. If your Brussels sprouts are slow to form sprouts, top the plant to stimulate their growth.