Diascia, Twinspur

Diascias are extremely popular, cottage garden, summer-flowering perennials. They're generally small with vertical spikes of tiny flowers that add a colourful, carefree touch in shades of mauve, pink and orange.

Recommended varieties

Diascias tend to be short spreaders. They were traditionally used in rock gardens, but are more successfully grown near the front of a mixed border, where they can fill spaces. Diascias love inching over a top surface of gravel. Planted densely, most make excellent ground cover in full sun, although you can never be certain they'll survive winter. Take cuttings as a precaution.

The following generally grow to about 25cm (10in) high by 50cm (20in) wide.

D. barberae 'Blackthorn Apricot': has a soft, warm wash of apricot-pink flowers, while 'Ruby Field' has fresh pink flowers. The Royal Horticultural Society has given both its Award of Garden Merit (AGM).
D. fetcaniensis : a lovely show of soft-pink flowers.
D. rigescens : a useful plant at the edge of a rock garden, where its trailing growth and pink flowers can gently dangle down. Its height rarely exceeds 30cm (1ft), although it’ll spread by nearly twice that. The Royal Horticultural Society has also given it the AGM.
D. 'Rupert Lambert': an excellent show of deep-pink flowers (an AGM recipient, too).
D.stachyoides: among the tallest of the species, growing to about 45cm (18in) high. It has mauve-to-pink blooms, each with a darker centre.

Growing tips

Site and soil preferences

Diascias like free-draining soil (limy, neutral or acid) and, although they tolerate poor conditions, will flower better and spread more confidently if the ground has a crumbly structure. Good sun is vital.

Planting associations

In borders, diascias can be very effective among the silvery foliage of artemisias or Stachys byzantina . Diascias also work well with other pinks, especially perennials such as Astrantia major , low blue penstemons, and some of the campanulas. Try sowing Anagallis monellii among them for added effect. The intense blue flowers look terrific scrambling among salmon twinspur.

Most diascias also thrive in hanging baskets, giving their best display if planted so they develop into a flowering globe. If well fed and watered, they'll flower all summer. In pots, they combine well with fellow South African plants such as blue felicias. Or mix them with trailing blue lobelias and white or pink argyranthemums.

Aftercare

Make sure your plants are well watered in dry spells. When used in a border, an annual feed is sufficient. If planted in containers where their roots are a little more restricted, feed at least every three weeks. If plants get tired and leggy, cut off old flower stems and trim back to encourage new growth.

Propagation

Propagation is simple. Cuttings will root, given bottom heat, within days during the growing season. But you can also dig out chunks of diascia at any time, or pull sprigs or tiny divisions from them and, provided they have roots, simply replant.

Diascias will often survive outside over winter. But, to play safe, take cuttings in September and root them in a greenhouse propagator. Keep them in 9cm (3½in) pots for planting outside the following May. If you don't have a greenhouse, cover your outdoor diascias with a bulky winter mulch or conifer clippings for extra protection.