Dahlias

Inspiration for a colourful border

What better antidote to the decline of high summer than the dahlia? Brash, bright and beautiful, dahlias bring joyous colour to the garden at the time of year we need it most. For years, dahlias were deeply unfashionable, but thanks to gurus like Christopher Lloyd and Sarah Raven, dahlias are popular again in the garden – and the bolder the better. The origins of the dahlia lie far from the over-bred marvels that we see on the show-bench. Exotic Mexico is their true home, where they grow wild on the open slopes of mountains. These simple, usually single-flowered dahlias are a world away from the elaborate forms that we have come to associate with the plant, and were originally grown not for their flowers but for their edible tubers that were used in medicine. It wasn’t until the late eighteenth century that dahlias arrived in Europe. It didn’t take long for people to realise that, grown from seed, dahlias produced variable and interesting results, giving rise to many different hybrids, and throughout the next two centuries the plant has been bred by horticulturists and amateurs alike to produce the tremendous range of forms available today.

Despite preconceptions, dahlias are extremely easy to grow. In Britain, dahlia tubers are traditionally lifted and stored inside over winter, but in many areas of the country it is possible to leave them in the ground all year round, provided you give them an insulating mulch of leaves or straw before the first frosts. If they are dry, freezing temperatures should be bearable: it is when they are left in a cold wet soil for prolonged periods that they will rot. If you lift your dahlia tubers, keep them dry over winter by storing them in sand or straw. Replant them in pots in April and keep them under cover until late spring, or plant them straight out in the ground in late spring. Water them regularly until they start to sprout - but don’t over-water - and then continue to water well once they are really growing quickly, being careful not to let the compost dry out. One of the most pleasurable things about growing dahlias is taking cuttings to make more plants, which you can do when you first see the tubers sprouting. Wait until a leaf sprout is 5-6cm long and then cut it from the tuber, taking a tiny slice out of the tuber at the same time. Dip the cutting in rooting powder and plant it into a small pot - or place several cuttings round the edge of a larger pot, which can encourage the cuttings to root quicker. Water and put a plastic bag over the pot to keep humidity in, and keep an eye on it until it is visibly growing. Watch my video showing you how to do it here.

When you’re ready to plant your dahlias out in the garden, choose an open, sunny spot with well-drained soil, and prepare the site carefully with generous amounts of well-rotted manure or compost. To make a bushy plant with plenty of flowers, pinch out the growing tips as the plant gets bigger, and water regularly if the weather is very dry. Grow species dahlia from seed, or seed strains like 'Bishops Children'. Sow under cover in early to mid spring and they should flower the same year.