Plant of the Month - Dahlia

Dahlia

Striking, sculptural, vibrant.

Plant: Ball Dahlia (Dahlia Asteraceae)

Striking and sculptural – no two words better describe the humble dahlia! Coming in a range of colours, sizes, and forms, they’re a beautiful addition to any summer garden. And being relatively easy to grow, they’re perfect to any gardener.

Ask any dahlia grower which is their favourite, and you’ll be hard-pressed to get an answer. The colours range through the entire rainbow spectrum, and can vary in size from tiny lollipop blooms to gigantic dinner plate flowers. Dahlias come from a genus of tuberous plants, being related to sunflowers, daisies, and chrysanthemums, and the varieties are numerous; some of the more common types include cactus dahlia, anemone dahlia, water lily dahlia, decorative dahlia and ball dahlia.

Dahlia tubers are best planted in spring – early summer, with flowering occurring late summer – autumn. Some tree dahlias even flower into early winter! They look their best when layered in mixed beds either as borders or in amongst plants of similar height, or as a mass planting by themselves. Choose a position with full sun to light shade, and protected from wind. Taller varieties will need staking as they grow – those vibrant flowers may tip the plant over!

As dahlias grow, they do not require much water until they’re over 15cm high – the tubers could possibly rot if overwatered during this time. Once they flower, we strongly encourage you to cut or pick the flowers. They make an incredible display in a vase, but it also encourages the plant to flower further.

Once all the bloom are gone, and the leaves change colour, cut them off at ground level for their dormant phase. Depending on the severity of winters in your area, you can dig up the tubers, cover with dirt or sawdust to prevent them drying out, and store until spring, when you can plant them again. Not only does this protect the tubers from rot over winter, but it gives you the opportunity to divide them for the next season.

Dahlias are a favourite with our volunteer gardeners – they are planted in the beds in the Walled Garden, adding colour to areas after the peonies and roses have past their best time. Whilst we predominately have the ball dahlias, there are occasionally decorative dahlias and cactus dahlias on show also.