Spice up your garden with roscoeas

By: Sue Skinner - 13/05/2011


If you want to spice up your garden then take a look at the exotic roscoeas. They are part of the ginger family, but are fully hardy in the UK and flower from now until late summer.

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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.

 

The yellow form of Roscoea cautleyoides

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.

 

Flowers of Roscoea humeana

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.

 

The white form of Roscoea humeana The purple form of Roscoea cautleyoides

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.

 

The bright red Roscoea 'Red Gurkha'

Roscoea purpurea 'Red Gurkha' flowers in July and August (Image: Richard Wilford)

 

Cultivation

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. 

 

Repotting roscoeas The Roscoea frame in the Alpine Nursery

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 -

 


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About us

Looking north towards the Davies Alpine House from the Rock Garden

Several people contribute to the Alpine and Rock Garden Team blog. Richard Wilford is the Collections Manager in the Hardy Display Section at Kew. His responsibilities include all the areas where alpines are grown at Kew Gardens. The three team leaders, Joanne Everson, Graham Walters and Katie Price, each have their own particular parts of the Gardens to look after. Between them, these four experts have over 55 years experience of growing alpines.

Alpines at Kew Gardens are not only grown to create colourful and informative displays, they also play an important role in the research Kew carries out around plant naming, classification, biodiversity and conservation.

Mountains are found on every continent and each range has its own unique alpine flora, but these plants are under threat from climate change. As temperatures rise, alpines are forced higher and will eventually have nowhere to go. The alpine collections at Kew are studied to help us all understand the mountain flora better and make informed decisions about protecting its future.

"Probably the most beautiful glasshouse in the world is the Davies Alpine House at the Royal Botanic Gardens Kew", John Hoyland, Gardens Illustrated, April 2011

Richard Wilford has written a book on alpines, 'Alpines from Mountain to Garden', published by Kew Publishing. You can buy it in the Kew shops or from Kewbooks.com.

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