Plant guide: Dahlia

Dahlias are popular garden plants admired for their wide range of colours, flower forms and sizes. Blooms can be as small as pompon types measuring less than 5 cm in diameter, or as large as decorative dahlias with flowers exceeding 30 cm across. Depending on the variety, flowers may be single, semi-double or fully double. Dahlias are grouped into several classes based on flower shape, including single, anemone-flowered, collarette, waterlily, decorative, pompon, cactus and semi-cactus types. Plant height varies from about 30 cm to nearly 1.5 metres. Dahlias have a long flowering season, running from mid-summer until late autumn, making them highly valued for adding late-season colour to the garden.

How to plant

Dahlia tubers are planted from mid- to late spring, once the risk of frost has passed. They are placed with the eyes facing upwards at a depth of approximately 10 to 15 cm. Plant spacing depends on the size of the variety: small types are spaced about 30 cm apart, while large varieties require 75 to 100 cm between plants. Dahlias thrive in well-drained soil enriched with plenty of compost, as they are heavy feeders. Tall varieties should be staked at planting time to prevent wind damage later. Tubers can also be started earlier in spring under cover in a greenhouse and planted out after the last frost.

Flowering period

The flowering period begins in mid-summer and continues until the first frost. During this time, dahlias produce an abundance of colourful blooms. Regular watering is essential, especially during dry periods, and plants benefit from monthly fertilising or liquid feeding every two weeks once flower buds appear. Removing faded flowers regularly helps to extend the flowering season and promotes the formation of new buds.

After flowering

After flowering ends in late autumn, dahlias require protection from frost. In light, free-draining soil they may survive in the ground, but in heavier soil or colder regions it is best to lift the tubers. Cut the stems back to about 15–20 cm above ground level, carefully lift the tubers and remove excess soil. Allow them to dry, then store them in a cool, frost-free, covered with sand, soil or peat. In spring, the tubers can be replanted to start a new growing season.

Tip:
Dahlias perform best in rich, fertile soil and full sun. Regular removal of spent flowers encourages continuous blooming and keeps plants looking neat throughout the season