About
Dahlia merckii, the Merck dahlia, is a slender, tuberous-rooted perennial to around 2 m with many-branched stems and substantial, divided, fresh-green leaves. Single, daisy-like flowers in pink, purple or white with a purple or yellow centre are produced in profusion throughout summer and autumn. A graceful and refined dahlia species for a sheltered, sunny border.
About the genus
Dahlia are tuberous-rooted perennials from Mexico and Central America with pinnately divided leaves and showy flowerheads � single to fully double � in virtually every colour except blue, produced in summer and autumn. Among the most versatile and floriferous of all tender perennials for beds, borders and cutting gardens.
Growing conditions
SunlightFull sun
Soil typeChalk, Clay, Loam, Sand
Soil pHAcid, Alkaline, Neutral
Soil moistureMoist but well-drained
AspectSouth-facing, West-facing
ExposureSheltered
UK hardinessH3
Plant details
Plant typeHerbaceous Perennial
HabitClump forming
FoliageDeciduous
Height1.5-2.5 metres
Spread0.5-1 metres
Time to full height2-5 years
Suggested usesCottage and informal garden, Wildlife gardens
Native toMexico
Care notes
CultivationPlant tubers 10-15cm deep in fertile, humus-rich, well-drained soil, in full sun. Cut back to near ground level in mid-autumn. In mild areas, and on well-drained soils, leave the tubers in the ground and protect with a deep, organic mulch. In colder areas, or on heavy soils, lift and store the tubers and replant in late spring after all danger of frost has passed. See dahlia cultivation and our video How to plant dahlia tubers and care tips
PruningDeadhead to prolong flowering
PropagationPropagate by basal softwood cuttings taken in spring from shoots from stored tubers, or divide clumps of tubers ensuring that each division has a viable bud
Pest resistanceMay be susceptible to aphids, capsid bug, earwigs, caterpillars, slugs, glasshouse red spider mite and onion thrips
Disease resistanceMay be susceptible to powdery mildews, dahlia mosaic virus, cucumber mosaic virus, tomato spotted wilt virus, storage rots, leafy gall, crown gall, dahlia smut, grey moulds, fungal leaf spot, phytophthora, sclerotinia and verticillium wilts