Growing Dahlias

Dahlias are easy to grow classic that will provide you with beauty from mid-summer to autumn. Every late-summer garden deserves these showstoppers! 

  1. Dahlias can be started in one of two ways. The tubers can be started indoors in pots, 4-6 weeks before planting them out. Simply find your last frost date and count back 4 to 6 weeks. Use a good quality potting soil. This method provides the dahlias with a head start and is especially helpful for those with relatively shorter summers. Be sure to harden off the plants before planting outdoors.

  2. Tubers can also be started by planting them directly into the ground. Here at AVF (zone 5), our season is long enough to plant tubers directly into the ground early to mid-May, without a head start indoors. Be certain that the ground has warmed up to a temperature of 15 Celsius (60 Fahrenheit) before planting out.

  3. Select a site in full sun and well-draining soil. Dahlias require a minimum of 8 hours of direct sunlight to perform at their best. Amend the soil by working in 2-3 inches of compost and organic fertilizer. Plant the tuber horizontally with the eye facing upwards and at a depth of 4-6”.

  4. In a garden border, space your dahlias 18-24” apart. This will give the plants plenty of room to mature into full, lush plants. If you are planning to grow for cutting, tubers can be planted much closer, approximately 12-18” apart.

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  5. While dahlias require plenty of water when actively growing throughout the season, it is important that you do not begin to water the tubers until after you see the green sprouts begin to break through the ground. Watering before this point can lead to the tuber rotting.

  6. Once the plants have reached a height of 12”, pinch the central growing stem by snipping it just above the third leaf pair. This will promote branching and increase flower production.

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  7. Taller varieties of dahlias (over 3’) tend to become top-heavy as the season progresses and will require staking to keep them upright. Insert a sturdy post/stake into the ground next to the tuber at planting time. As the plant grows, secure it to the post with twine. Tomato cages, available at most garden centres or hardware shops, also work well.

  8. Don't be afraid to cut your dahlias and enjoy them indoors. With dahlias, the more you cut, the more you get! If you aren’t growing your dahlias for cutting, you’ll want to stay on top of deadheading (removal of spent flowers) to keep the plants blooming well into the season.

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