Rose Trees: A Double Take /
Putting the spotlight on the versatile and much-loved rhododendron
It has been said that a garden is a friend you can visit anytime, and from a gardener’s
viewpoint time has been on our side in recent months as plants continue to follow their
normal seasonal routine. Lately there’s been an opportunity to ‘keep it local’ and take the
chance for a second look at familiar plants closer to home. Rhododendrons, named from
Greek via Latin rhodon (rose) and dendron (tree) are a good case in point.
of us have a rhododendron or two, even if space is tight and they’re in a pot or container. In larger spaces there’s room for more, and they provide an evergreen structure to the garden which is particularly valuable in the winter when deciduous trees and herbaceous perennials lose their leaves or retreat underground.
The rhododendron genus is one of the largest in the plant kingdom with nearly 1000 species, found mostly in the Northern Hemisphere and concentrated in Central and East Asia. Over a century of ongoing hybridising and selections from the native species brought to the West has resulted in a greater variety of flower colours and the typical plant that we’re familiar with: around 1.5–2.0 m high and broad, with smooth, medium-sized green leaves and rounded trusses of flowers.
All well and good, and many beautiful varieties have been bred in New Zealand. However, as the climate slowly changes, it makes sense to plant more selectively and avoid potential problems on the horizon. For example, modern rhododendron hybrids (and other evergreen shrubs) suffer more often now from thrips and mites, tiny insects which together turn the leaves a silvery colour and can defoliate a whole plant in late summer and autumn. Some hybrids have less of a problem, and certain rhododendron species and first generation hybrids between them have a dense, almost suede-like coating on their leaves and stems which deters thrips. They have a wide range of growth habit, leaf and flower shapes and sizes, and some are strongly scented. They’re specially adapted to different conditions in their home environments so we can pick a species, for example, that’s more tolerant of drought and heat.
The best eco-friendly way I’ve found to control thrips and mites on smooth-leafed rhododendrons and other evergreens is to spray thoroughly (including stems and under the leaves) in cool conditions, using Conqueror oil at no more than 10 ml per litre of clean water. And including a little copper powder at the rates on the box will help to clean up any sooty fungal residue. A spray every fortnight or three weeks from January to April is usually sufficient, and there will be less of an issue the following season.
Here are some favourites I wouldn’t be without, thrips or no thrips: ‘Rubicon’, ‘The Honourable Jean Marie de Montague’, ‘Bibiani’ and ‘Ilam Cornubia’ (reds); ‘Karen Triplett’, ‘Phyllis Korn’ and ‘Ken Burns’ (butter yellows); ‘Lemon Lodge’ (pale greenish yellow); ‘Helene Schiffner’ (palest pink fading to white), ‘Lalique’, ‘Van Dec’ and ‘Countess of Haddington’ (shell pink); ‘Everest’ (white); and ‘Bumble Bee’ (clear violet-purple).
Rhododendron species and hybrids with a dense furry coating on their leaves – properly called indumentum (meaning ‘garment’ in Latin) – are a diverse bunch. Original species have developed this coating to shield them in their natural environment, in the same way our native Marlborough daisy shrub Pachystegia has thick cream-coloured indumentum under its leaves, protecting it against drought, heat and salt spray.
Rhododendrons with this luxurious suede effect have a distinct personality, like a display of teddy bears; and even more so when we understand how indumentum helps them thrive.
Most are native to relatively harsh high altitude areas with