Dahlia Plant Growing & Care Guide for Gardeners

Article by Dean Ravenscroft, Ph.D. - Updated 14th Oct 2023

In this Gardener's HQ guide, we'll explore cultivating Dahlia plants in your garden, indoor spaces, and other settings.

Dahlia: Cultivation & Garden Use

Although Dahlia are half hardy perennials they are normally grown as a half hardy annual by gardeners.

Depending on the variety, they come into flower from the middle of summer to the first frost of winter. This makes a great plant to grow if you wish to bring some fall color into the garden.

Some of the bigger varieties of Dahlia can reach heights of five feet (1.5 m) or more, and carry double flowers in a large range of colors.

Dahlia (tiptoes) pictures by KaCey97007.

How to Grow Dahlia

Dahlia can be grown from either seed or tubers. If growing from tubers then plant with the eye towards the surface at a depth of about 15 cm (after the last frost of spring).

The seeds of Dahlia should be lightly covered once sown (before the last frost of spring).

Ideally Dahlia should be planted into an area of the garden that is sunny; spacing depends on variety, small (30 cm / 12 inches), medium (45 cm / 18 inches), large (65 cm / 25 inches).

They like a soil that is of pH6 to 7.5, and that is enhanced by the addition of bone meal and humus, and low in nitrogen.

Seedlings of Dahlia can first be grown indoors for later transplanting. They should be started about 10 weeks before they are due to be put outside in the middle of spring.

They normally takes from one to three weeks to germinate in individual pots at about 18°C.

Dahlia Chick A Dee by F. D. Richards.

Caring for Dahlias

Once growing in the garden Dahlias should be fed by the use of bone meal at the beginning and end of summer. Dahlia should be watered in prolonged dry periods, and weekly when in bloom.

Quick Dahlia Growing Guide and Facts

• Common Names: Dahlia. Common Cultivar classes are Ball Dahlia, Cactus Dahlia, Pompom Dahlia, and Waterlily Dahlia
• Family: Asteraceae. As a member of the Aster plants it is closely related to plants such as Daisies, Palm Spring Daisy, and Canary Marguerite.
• Life Cycle: Half hardy perennial usually grown as a hardy annual by gardeners.
• Height: 12 to 60 inches (30 to 180 cm).
• Native: South and Central America.
• Growing Region: Zones 3 to 10. As a perennial in zones 9 and 10.
• Flowers: Summer to first frost.
• Flower Details: Purple, violet, yellow, red, pink, white. May have large flowers. Often have double flower heads.
• Foliage: Blue-green. Ovate. Serrated.
• Sow Outside: Tubers: plant about 6 or 7 inches (15 to 18 cm) deep with the eye at the top following the last frost. Seed: Cover seeds. Two weeks before last frost. Spacing: small species: 12 inches (30 cm); larger species 20 to 36 inches (50 to 90 cm).
• Sow Inside: Pots. Germination time: one to three weeks. Temperature 68°F (20°C), ten weeks in advance. Transplant outdoors in mid-spring, well after any chance of frost.
• Requirements: Full sunlight. Soil pH 6 to 7.5. Deep soil. Humus rich. Add bone meal. Low nitrogen. Provide support. Occasional feed with bone meal. Pinch tips. Deadhead. Bring tubers indoors for the winter in areas of frost. Propagate: dividing in autumn.

Common Questions

How many members does the Dahlia genus have?

The Dahlia genus currently has approximately 42 species.

Are Dahlia species suitable for garden or landscaping use, and if so which ones are commonly chosen by gardeners?

Yes, Dahlia species are a popular choice for gardens and landscaping due to their vibrant and ornamental blooms. Among the Dahlia species, Dahlia pinnata (Garden Dahlia) is the most frequently grown by gardeners.

Are members of the Dahlia plant genus fragrant?

Most Dahlia species are not known for their fragrance, but are admired for their beautiful blooms.

Is Dahlia invasive in the USA, if so in which states?

Dahlia is not considered invasive in the USA.

How do I remove Dahlia plants from my garden?

To remove Dahlia plants, dig them up, ensuring to get all the tuberous roots to prevent regrowth.

Summary

The Dahlia genus is a group of tuberous plants native to Mexico. They have vibrant, diverse flowers that come in a wide array of sizes, shapes, and colors. Dahlias are prized for their late summer to fall blooms, and I like to use them to help bring color into the garden as other flowers start to wane.

To grow Dahlias, you should plant the tubers after the last frost into a sunny location with well-draining soil. Plants will require consistent moisture, but avoid waterlogging them. Simple care involves supporting the larger varieties with stakes, and removing some of the side buds to help enhance the size and quality of the main flower.

I hope that you enjoyed this guide on how to grow Dahlia Plants. You may also enjoy the following Gardener's HQ Asteraceae growing guides: How to grow Safflower and Crepis plants.