Sunday, 20 May 2007

When is a Canna not a Canna?

A Canna certainly is not a Canna when it is Thalia dealbata.

Commonly known throughout the southern states of the USA as "Water canna" or powdery thalia, it is a rhizomatous marsh or marginal aquatic perennial that features long-stalked canna like foliage and violet blue flowers.

It is a tall plant, 2-3 metres (6-10'), that lends a tropical flavour to ponds and water gardens. It is native to swamps and ponds from South Carolina to Florida west to Missouri and Texas. It is rare to Missouri, its distribution being limited to swampy areas in the southeastern lowlands region.

The species features paddle-shaped to lanceolate-elliptic blue-green canna-like leaves 50cm (18") long, on petioles to 70cm (24") long. Foliage is dusted with white powder. Violet flowers appear in branched open panicles 20cm (8") long, atop of scapes typically rising well above the foliage to 2 metres (6') , less frequently to 3 metres (10') tall. It blooms July and August. The genus name honours a 16th century German physician and naturalist, Johann Thal.

As far as cultivation is concerned, Thalia dealbata grows in wet soils or in shallow water in full sun. It grows best in organically rich loams. Plants are considered winter hardy to USDA Zones 6-10. In St. Louis, plants are best grown in containers either sunk in wet mud near the water line or submerged in up to 60 cm (2') of water.

Plants may also be grown in wet boggy areas. Containers covered by 50-70 cms (18-24") of water will generally overwinter in place. Consider bringing other containers indoors to a greenhouse or other frost-free area with bright light. For plants grown in wet boggy soils, just cut back stems and mulch heavily in winter.
The plant has no serious insect or disease problems.