Roscoea is a not very well-known tuberous perennial that is grown for its eye-catching flowers and tolerance of wet and shady conditions. It belongs to the family Zingiberaceae — the ginger family — and originates from high altitudes in the Himalayas and Sichuan as well as Yunnan in China, where it has evolved its tolerance to non-tropical or sub-tropical climates.
They are prompted into growth at the start of the monsoon season, emerging in late spring and early summer. There are 22 recognised species, of which eight are endemic to China. The genus was named by the British botanist James Edward Smith after William Roscoe, a botanist who helped establish Liverpool’s botanic garden.
In midsummer Roscoea produce flowers that have been likened to irises or orchids with their distinct form of one hooded top petal and three lower petals. The lower petals are in fact sterile stamens, two of which are fused together to form a landing pad for pollinating insects.
The flowers come a few weeks after the green pseudostems, made up of extended leaf blades, and are borne in a spike at the end of the pseudostems in a variety of colours. R. cautleyoides has clear pale-yellow flowers that reach a height of 30cm in June to August, while R. purpurea ‘Red Gurkha’ has red stems and red flowers. If planted in the shade, the flowers are long-lasting and can be on display for between four and six weeks. But exposure to hot sun will cause them to shrivel.
The tubers needs to be planted deep underground — the crown should be four-to-six inches beneath the surface — and protected from frost with mulch for the first few years. They will tolerate light sun as long as plenty of moisture is available during the summer. In fact, if grown completely in shade the pseudostem will become very long and they will have a tendency to fall over.
They grow well with woodland understory plants and bulbs, and can be used to extend the flowering season in a woodland or a rock garden. Good winter drainage is essential and they do not survive well in pots. Large plants will need to be divided every three-to-four years in the spring, before the tubers start to grow.
Despite their exotic appearance, Roscoea are quite hardy and the tubers are well able to survive British winters. However, they can be susceptible to slugs should they be grown in very damp conditions.
What the specialists say
Bleddyn Wynn-Jones, co-owner, Crug Farm, Wales
"The best ones are the R. purpurea, which are larger than a lot of them. As well as being larger they flower a lot later and also flower a lot longer, through October and even into November sometimes.
"‘Red Gurkha’ and ‘Brown Peacock’ are very popular because of their much bigger flowers. ‘Brown Peacock’ has coloured foliage as well that comes up purple and gradually turns a bit green when the flowers come out.
"We have our own collection with much paler flowers — almost white for a lot of them. They’ve always been very popular here and they are available from garden centres at the more specialist end.
"With the ginger family you have to make sure that the drainage is good. In clay, don’t expect them to live long. There are a lot of people creating new hybrids. It’s a big group and hybridising works well. New ones are always very difficult to get hold of — there are very small numbers available."
Graham Gunn, Kevock Garden Plants, Scotland
"There are 30 varieties in our bulb catalogue. Roscoea is one of those plants that come out quite late and a lot of people are not that familiar with them. It’s quite unusual.
R. cautleyoides and R. tibetica are two that we sell."
Dave Ward, garden nursery director, Beth Chatto Gardens, Colchester
"We grow quite a few and they are easy to grow. They have interesting tubers, which we split in spring as they come into growth and pot on for sale. I always knew them as the ‘poor man’s orchid’ or ‘garden gingers’.
"A nice one is ‘Red Gurkha’, which is relatively popular and goes well when we put it out. R. cautleyoides are the most common. We grow a nice one called ‘Kew Beauty’, which has a yellow flower.
"There are no real pest and disease problems, though slugs might be a slight issue in damper areas. One disadvantage is that they can be a bit untidy after they have flowered and flop a bit, so we prop them up. We grow them in semi-shade with hostas, tiarellas and shade grasses, but I have seen them at Kew in the rock garden out in the open."
John Winterson, deputy buyer, RHS Plant Centres
"Roscoea are a great genus that have an exotic feel and look about them yet they are easy to grow. They are happy in partial sun or even full sun in cooler parts of the country. They like plenty of water when growing, but keep them drier during winter dormancy to prevent rotting.
"You can also grow them successfully in containers, so they are easy to keep looking good when on the shop floor. We sell them from our A-Z herbaceous sections and on tables en masse when in flower for impact and to attract customers to them. They grow very successfully at Wisley and put on a great show, which obviously helps to sell them.
"R. cautleyoides is the best seller at all of our centres, followed by R. scillifolia and R. humeana. Our range also includes R. cautleyoides ‘Early Form’ and ‘Kew Beauty’. My favourite is R. purpurea ‘Wisley Amethyst’, despite still being quite tricky to get hold of."
Species and varieties
R. alpina has large purple flowers and is frequently planted in rock gardens. Height: 15cm.
R. auriculata Award of Garden Merit (AGM) (H5) bears purple flowers and originates from Nepal. Height: 25-55cm.
R. × beesiana alba has pale-yellow flowers on top of pale-green leaves. The flowers have highly variable purple streaks through the petals. It
is a hybrid between R. auriculata and R. cautleyoides. Height: 35-40cm
R. cautleyoides bears yellow, white or purple flowers and originates from China. Height: 55cm.
R. cautleyoides ‘Kew Beauty’ AGM (H5) features large yellow flowers. Height: 45cm.
R. cautleyoides ‘Purple Giant’ has large purple flowers and comes into flower early in May.
R. procera bears deep-green lance-shaped leaves that can grow up to 25cm long. The flowers are purple and white.
R. purpurea has large, orchid-like blooms in pinky purple or that are sometimes white or bicoloured. Having been in British cultivation since as far back as the 1800s, it has produced many garden varieties. Height: 25-40cm.
R. purpurea ‘Brown Peacock’ is a late-flowering variety that produces large purple flowers from August to September. It also has large dark-red-backed foliage. Height: 55cm.
R. purpurea ‘Nico’ is a compact variety reaching heights of 20cm. It produces large deep-purple flowers from July to September and has red and dark-green foliage.
R. purpurea f. rubra AGM (H4) is intolerant to too much sun. It bears red flowers with tissue paper-thin petals and a red pseudostem.
R. tibetica is a short variety growing to a height of 15cm. It features two-toned flowers of magenta purple and white.
R. cangshanensis is a newcomer to the genus, described as recently as 2000. It is relatively short in stature with deep-pink flowers. If planted deeply it will survive very cold winters because it originates from altitudes of more than 2,600m in the mountains of Yunnan in China.
Thank you to Floramedia, which supplied the images for this article from its photo library