These rather exotic-looking plants, loosely allied to the ginger family, look like irises to some and orchids to others. Their appearance seems to suggest a lack of hardiness to gardeners, however these tuberous, rooted plants are hardy if planted deeply.
Roscoeas grow in grassland, on screes, or on the edges of deciduous woodland at moderate heights of 1200–5000 metres (4000–16000 ft) along the Himalayas and into China. There are up to 17 species in all and eight are found in China. They are prompted into growth at the start of the monsoon season, emerging later than most plants, so they enjoy late-spring and early-summer rain but actively resent dry weather and scorching sun.
Roscoeas form tuberous roots that resemble small dahlia tubers. These push downwards to form vertical roots in the soil, before dying back in winter to leave a gap. These tubers are very vulnerable if left in a pot during winter, so if you buy a roscoea do plant it as soon as possible and as deeply as you can. Otherwise you may lose your plant.
The stems of roscoeas are formed from tightly wrapped leaves and these can colour up in some cases. A good form of ‘Red Ghurka’ will have red stems and red flowers, for instance. The flowers are unique, having a hooded top ‘petal’ and three lower ‘petals’, looking rather like slipper orchids in shape.
Where to plant
They prefer semi-shade but will tolerate a sunny position if plenty of moisture is present during the summer. Avoid deep shade which will draw the plants up, making them floppy, and reduce leaf colour.
Roscoea flowers are long-lasting in shadier positions, giving four to six weeks of interest. The flowers of most can shrivel in hot sun, so site them carefully.
How to plant
The top of the crown should be planted four to six inches below the soil level. As the plant settles in, the tubers will go deeper, but if your garden is cold it is best to surface mulch for the first three years to provide extra frost protection. Use bark in the woodland garden, or gravel on a scree, as your mulch. Mark their positions well because they are much later to appear than most plants. Be patient and water the ground well in dry April and May weather to promote growth.
When to divide
Divide large roscoea plants every 3-4 years in April, before the tubers begin to grow.
Roscoeas are extremely useful in woodland gardens, grown in light shade, as they perform after most woodlanders and extend the flowering season.
They associate well with spring woodlanders, bulbs and ferns in the dappled shade provided by deciduous trees and shrubs. Other shorter forms, found naturally on screes in the wild, are perfect for the alpine slope in sunnier situations. So you do need to select your varieties and forms. Good winter drainage is essential for both types, but alpine screes and woodland gardens tend to have good drainage.
Roscoea x beesiana cream group
Strong growing, to 40cm. Lots of big cream (not white and not pale yellow!) flowers over an unsurpassed flowering season.
Roscoea x beesiana ‘Monique’
White, not cream, flowers on a vigorous plant. Variable purple veining on the lip. Long season.
Roscoea cautleyoides ‘Early Purple’
The first to flower, short and stout, a nice soft purple.
Roscoea cautleyoides ‘Yeti’
Substantial flowers of a warm, light yellow, which are particularly frilly.
Roscoea humeana ‘Rosemoor Plum’
Deep plum flowers, quite early in the season, on a plant which clumps quickly. It needs a cool spot though – the flowers are prone to bleach under hot, bright conditions.
Roscoea ‘Long Acre Sunrise’
A pale-yellow mid-season hybrid not the earliest from Nigel Rowland of Long Acre Plants.
Roscoea purpurea ‘Brown Peacock’
Purple flowers, in later summer as usual for this species; brown-tinted leaves and dark, brownish leafy stems.
Roscoea purpurea ‘Red Ghurka’
Highly desirable with large red flowers on a short stout plant with dark red stems. This is very late into growth and late flowering too, in mid-August - September. Not quite as hardy as some others, so find a sheltered spot.
New breeds of roscoeas
Plant breeders, including Robin White of the now-closed Blackthorn Nursery in Hampshire, have bred several new forms. John Massey, of Ashwood Nurseries has taken over from Robin and now sells White’s Royal Purple Hybrids. These showy purple roscoeas have stripy purple-hued dusky foliage. Hugh Nunn of Harvington is also breeding them. His include the purple ‘Harvington Purple Star’, the ivory-white ‘Harvington Raw Silk’, the narrower-flowered ‘Harvington Royale’ and the pale-mauve ‘Harvington Amethyst’. Prices tend to be low because roscoeas are struggling to be accepted. However they are good garden plants and deserve to be planted more widely.
Did you know...?
Roscoea were named by an English botanist James Edward Smith in 1806 to honour his friend william Roscoe, the founder of the Liverpool Botanic Garden. Roscoe was known to have been interested in "gingers" (Zingiberales) and to have grown a number of them.