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Included among our New Zealand native plants are some very interesting species from widely differing genera that have all developed a similar bushy growth habit of dense wiry twigs with little or no foliage on the outside of the plant. The leaves and flowers appear behind a protection of fine, often pointed, overlapping outer branches and twigs.
This growth style is known as divarication or a divaricating habit. The name is derived from the Latin word divaricare, which means to spread apart, and refers to the very sharply angled branches (the stems are often at about 90° to one another) of these shrubs.
There are several theories as to why plants that are not otherwise all that closely related should develop such a similar growth habit. Obviously it was due to some environmental stimulus, but what? One suggestion is that it was in response to heavy browsing by Moas. Leaves and flowers that were inside the framework of the bush had a better chance of reaching maturity and so over a period of time the plants concentrated growth in these areas and developed their outer twigs into a protective layer. Another theory suggests that divarication is simply an adaptation to a very harsh, windy environment. Outer leaves and flowers would be desiccated by the wind or broken off under the weight of snow.
Having never encountered a moa, I can’t vouch for the authenticity of the first theory, but it is true that most divaricating shrubs naturally occur in very windswept environments that are also often quite dry. The areas that I am most familiar with, Christchurch’s Port Hills and the mountains of Canterbury, certainly fit the bill and such divaricating plants as Sophora prostrata, Corokia cotoneaster and Myrsine divaricata are all common.
So, you may ask, what significance does all this have for gardeners? Well, divaricating plants are all very hardy, they are natives, they grow in open, windy, rocky areas and they all have great character. In short, they are superb shrubs for exposed gardens.
When grown in good soil with shelter, regular feeding and watering, divaricating shrubs tend to look much like any other garden plant. Their true character only emerges under harsh conditions. If you have an area of your garden that seems to be exposed to wind from every direction and takes the full brunt of every passing storm, that’s the place to grow your divaricating natives.
Although these plants will grow in ordinary garden beds, a large open rockery is far more appropriate. They look their best when grown with other open-country plants and where the rugged nature of the rocks can be used to emphasise their unusual lines.
Few divaricating plants could be called spectacular, but they are superb for creating a harsh and rugged look. Rather than have brightly coloured flowers or foliage that stands out, the beauty of these plants is in the way they blend with their environment. Look at the photograph of Muehlenbeckia axillaris, the continual exposure to wind has moulded its form so that it has become almost an extension of the rock over which it is growing.
Divarication is just one form of adaptation. Other plants in the same environment use different survival techniques: some grow very close to the ground, others, such as the grasses, have very flexible stems, and still others, like the native gentians, become dormant and disappear underground for much of the year.
All of these plants can be grown in a large rockery and may be used in combination with exotics for the odd splash of vivid colour. The bright blue European gentians and the orange, red or yellow of the Asian geums blend well with the less intensely coloured NZ natives, provided such plants are used with restraint.
When most gardeners think of rockeries they think of alpine plants, but many of our New Zealand alpines can be difficult to cultivate. Mid altitude plants offer a wealth of forms and will grow in a wider range of climates and they are often just as effective as the true alpines while being far better adapted to our garden growing conditions.
However, it is important to realise that these plants have become adapted to living in a harsh environment and can suffer when grown under easier conditions. Sheltered, humid gardens and rich soil will lead to rank growth and a shortened lifespan. Divaricating plants and those that grow with them thrive with full exposure to the elements and are a great choice for country gardens that are open to the weather. Also, they are usually very frost hardy and will tolerate early and late frosts, so they are well suited to high-country or inland gardens.
Although the subject of rockery design and construction is probably best left for a later article, it may be wise to highlight a few of the main points. Rockeries, more than most other garden styles, attempt to replicate nature, so before building your rock garden, visit some of the natural rockeries that can be found in the hills and mountains.
Look at how time and the forces of nature have acted on the rocks. In stable areas where the rocks have settled and plants have started to grow, you will usually find that the rocks are well embedded and their grain tends to run in the same direction. Jumbled piles of loose rocks are unstable, liable to move and few plants will be found there. The screes that are common in the South Island mountains are so prone to movement that the plants that grow on them have many unique features that enable them to survive in such a harsh environment. Keep these natural variations in mind when creating your rockery and you will be able to create changes of mood in the design and will also be better able to cater for the particular needs of the plants.
You can use any rocks for a rockery but bigger is better and stick to just one type. Nature’s rockeries show very little variation in texture and colour — combining widely differing rock types is sure to look artificial and it also draws attention away from the plants.
Use plants that are compatible in style and growth habit, and don’t overplant. Remember those natural rockeries? Natural rock outcrops have far fewer plants than most rockeries. The structure and layering of the rock often captures your attention before the plants are even noticed and this is also a feature of the best garden rockeries. An overplanted rockery tends to look like a herbaceous border with rocks.
Try these hardy and adaptable natives. What you lose in immediate floral impact you may well make up for with improved survival rates, lower maintenance and greater overall interest.
Copyright Geoff Bryant
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