Dahlia 'Purple Gem' is an upright, tuberous perennial prized for vivid violet-purple semi-cactus flowerheads, whose long quilled petals create a dramatic spiky silhouette from midsummer until the first frost.
Plant tubers after frost in fertile, humus-rich, moist but well-drained soil in full sun. Stake early, water consistently during active growth and use a low-nitrogen feed to support flowers rather than soft foliage.
Deadhead often for continuous bloom and cut stems regularly for arrangements. In USDA zones 3–7, lift tubers after frost and store them cool, dry and frost-free; in zones 8–10 they may remain outdoors where drainage is reliable.