Delightful Dahlias

On 27th February ODGC welcomed back Pip Smith, formerly Head Gardener at Wollerton Old Hall and now a garden designer.

Pip began with a brief history of the genus. Native to Mexico and Central America where the tubers were eaten by Incas and Aztecs, the first dahlia, Dahlia imperialis, was discovered by a Spanish botanist sent out by Philip II to explore the region’s plant life. Present day dahlias are descended from three species, D. coccinea, D. pinnata and D. rosea. Hybridising freely, by the 1880’s American catalogues boasted 14,000 cultivars, this number rising to 50,000 by the C20.

Dahlias take many forms including single, pompom, cactus, anemone and decorative. Originating from the equator they are at their best in early autumn when day and night lengths are equal. They require moisture retentive fertile soil, cool to warm temperatures
shelter and regular feeding with a high phosphorous feed. A nitrogen rich feed is to be avoided as it results in over abundant foliage. They grow rapidly and should be staked early, twiggy branches provide a natural look.

Dahlias may be propagated by tubers, cuttings or seed, though the latter results in a lottery which can be rewarding. Tubers should be started off in Spring under cover and cuttings taken as the shoots start to develop. Free draining soils benefit from a handful of Growmore or Fish, Blood and Bone added to the planting hole in mid-May. The stems of dahlias destined for the showbench need to be disbudded, the second and third bud removed as soon as possible to allow the plant to develop a single flowerhead on a long, straight stem. After the foliage is browned by the first frost the plants should be cut back and the tubers lifted, turned upside down to drain, the soil brushed off and then stored in dry conditions covered with new compost or shredded paper. A dusting of yellow sulphur helps to ward off disease.

Pests include slugs and snails, earwigs and rabbits and they can also suffer from mosaic virus, crown gall and powdery mildew.

Pip thoughtfully provided members with a printed list to accompany his kaleidoscopic slide show demonstrating how the various hybrids can be grown and combined with other late flowering perennials and grasses to extend the gardening season into late autumn. Examples include D. Oakwood Diamond, white with a lavender centre which harmonises beautifully with Salvia Phyllis’ Fancy, white suffused with lavender and D. David Howard, burnt orange contrasting with white Phlox paniculata David.
Although rewarding dahlias are labour intensive and Pip cautioned against growing more than three hybrids – a test of self control when presented with such an abundance of colourful cultivars.

      Ghislaine Arundale