Clematis 'Bill MacKenzie'

Clematis 'Bill MacKenzie' was raised in 1968 by English gardener and breeder Valerie Finnis at the Waterperry School of Horticulture from a cross of C. orientalis and C. tangutica. She named it after her 'great friend and mentor' William Gregor MacKenzie, Curator of the Chelsea Physic Garden. In 1976 the cultivar won the RHS Award of Merit at an RHS show, and it later received the prestigious RHS Award of Garden Merit. Its 5–6 cm flowers are a vivid dark yellow, nodding bell-shaped, with four thick, slightly glossy tepals and distinctive dark purplish-brown stamens.

Growing to around 400 cm, 'Bill MacKenzie' is one of the most vigorous cultivars in the Tangutica Group and needs space to match: it quickly covers large fences, arbours, pergolas and trellises, and makes an excellent ground cover over larger areas. It thrives in sunny to partly shaded positions and tolerates dry, poor soils — waterlogged or heavy clay soils should be avoided. A wonderful autumn effect is created when silky silver feathery seed-heads develop alongside the last flowers, remaining decorative well into winter while the foliage often stays green until early November.

'Bill MacKenzie' is very hardy (zone 5, down to about -28 °C) and straightforward to care for: cut the plant hard back to 25 cm in March to encourage vigorous new growth and a generous flower display. If you want to enjoy the decorative seed-heads for as long as possible, you can delay pruning until early spring once the seed-heads have lost their ornamental value.