Spice up your garden with roscoeas
Roscoea is an Asian genus of 20 species, distributed along the Himalayan Mountains and into China and Myanmar (Burma). They are in the ginger family (Zingiberaceae), with rhizomatous roots that are dormant in winter. There are a number of subspecies and varieties, plus some hybrids and cultivars. Here at Kew Gardens we concentrate on the species and naturally occurring varieties. Most are grown in pots in the Alpine Nursery but some are also grown outdoors, especially in the Rock Garden.
Roscoea cautleyoides in the Rock Garden (Image: Richard Wilford)
When the plants come into flower, pots are moved from the nursery into the Davies Alpine House for display. Different species are in flower from May to August. The flowers look quite exotic and some people have commented that they remind them of orchids.
Roscoea humeana (Image: Richard Wilford)
Flower colour is generally a shade of purple or yellow but there are some white forms as well - we grow Roscoea tibetica forma alba and also R. humeana f. alba. In some the pale flowers can be nearly pink or may be so dark that they look almost black, such as R. scillifolia. There are two yellow forms in the Alpine House now: R. humeana f. lutea and the yellow form of R. cautleyoides. Here at Kew we have observed that the yellow forms tend to flower before the purple forms of the same species.
Left, Roscoea humeana forma alba, and right, Roscoea cautleyoides forma sinopurpurea (Images: Richard Wilford)
There is one plant that breaks from this general colour scheme and this is Roscoea purpurea 'Red Gurkha' from Nepal. As its name suggests, this plant has striking red flowers, sometimes with narrow white streaks on the lower petals. The stems are also flushed red in some forms.
Roscoea purpurea 'Red Gurkha' flowers in July and August (Image: Richard Wilford)
Here at Kew we repot the Roscoea collection in late January to early February, in a moisture retentive but well-drained compost, then plunge the pots in sand in an outdoor frame. The pots are watered in, then only the sand is kept damp until the first signs of growth in spring. Once they are in full growth they are kept well watered and shaded from the sun on hot days. Between the time the foliage dies back in autumn and repotting takes place in winter, both pots and plunge sand are kept completely dry.
Left, repotting roscoeas in January this year (Image: Graham Walters) and right, the Roscoea frame in the Alpine Nursery (Image: Richard Wilford)
We find most species propagate readily from offsets but they are also quite easy to propagate from seed, although this does mean it is longer before they reach flowering size.
- Sue -