Continuously changing display

Astilbe rivularis. Photo by Gerard O'Brien
Astilbe rivularis. Photo by Gerard O'Brien
Rushing down a Chinese hillside before the light faded, I grabbed some seed from a low-growing Astilbe rivularis.

Fast-forward 17 years and the progeny from that handful of seed here at Dunedin Botanic Garden has grown into a vigorous patch of striking foliage and swaying flower heads.

Astilbe rivularis is one of the largest astilbes which, depending on habitat and rainfall, can reach up to 2.5m. In the rhododendron dell species border Dunedin's moderate rainfall limits height to between 1.5m and 2m, as does competition from surrounding tree roots.

Most other astilbes in the dell flower in midsummer, but A. rivularis, although now at the end of its season, is a late-summer-flowering species. The frothy yellow-white flower heads are scented and add 50cm to the metre-high mound of coarsely divided dark green foliage.

Earlier in the season the leaves are a bronzy colour, creating an attractive two-tone effect above more mature foliage below. The leaf and flower stalks vary from yellow-green to reddish, with the red colour being particularly prominent in the flower stalks. They are also covered in coarse bronzy hairs.

From leaf emergence to late flowering, A. rivularis provides a continuously changing display far exceeding my expectations at the time of its hasty collection.

- Doug Thomson is curator of the Rhododendron Dell at Dunedin Botanic Garden.