Dahlia are tuberous rooted perennials with pinnately divided leaves and showy flower-heads, double in many cultivars, in summer and autumn
Single-flowered dahlias have flowerheads usually less than 10cm across, with one or two rows of spreading ray florets, surrounding a central boss of small tubular disc florets which are valuable for bees and butterflies
'Twyning's After Eight' grows to 1m, with very dark blackish-brown foliage and single white flowers 8cm across, with broad rays florets and a deep yellow central disk, opening from late summer