Bell flowers with N.Z. charm

Press, 5 December 1986, Page 18

Bell flowers with N.Z. charm

Axrdener’s w DIARY

Derrick Rooney

Colour in the rock garden will begin to taper off soon, and there will be a gap until the cyclamen and autumn bulbs begin to flower in February. Fortunately some longflowering or late-flower-ing alpines are available to fill in. Among them are the smaller campanulas.

These plants, known variously as bell flowers or hairbells, are summer stars of Northern Hemisphere rock gardens, and they grow well in the Southern Hemisphere, too, although they do not occur here naturally. We have our own alpine hairbells, belonging to the Southern Hemisphere genus Wahlenbergia, and although they do not have the flamboyant appeal of the northerners, they have charms of their own. New Zealand hairbells range from the very rare (Wahlenbergia tricho-

gyna, from one known site in Marlborough) to the very common (the übiquitous Wahlenbergia albomarginata). Throughout the summer and well into the autumn, the common New Zealand hairbell may be seen flowering in hilly and mountainous coiintry, in a variety of forms with broad or narrow leaves, and white or blue flowers, varying in size from a thimble downwards. It is hardy, and tolerant of drought.

Though the New Zealand hairbell is not in the top rank of alpines, several of its forms are worthy, of cultivation in rock gardens. Getting them established is the hard part. Seed, which is ripe from about mid-January onwards, affords a ready means of propagation, but seedlings vary in the size

and hue of their flowers and few gardeners have the time or space to grow 40 or 50 plants to supply the one superior form that they require. Vegetative propagation of plants selected from the wild seems like the obvious solution; unfortunately the problem is not straightforward. ,

Frequently, healthy looking clumps of largeflowered or dark blue forms of Wahlenbergia albomarginata, transplanted from the wild to rock gardens, seem to thrive for a few weeks, and then disappear, never to return. There is an explana-

tion for this, to be found in the relationship between the plant and its natural habitat.

In the tussock slopes and stony places where it grows, the New Zealand hairbell faces competition from larger species. Its seed often has little or no chance of germinating. To survive, the hairbell has adopted a device also used, though for different reasons, by scree plants.

The leaf-rosettes and flowers appear at the ends of stolons, long, underground runners which thread among the tussock roots or rock crevices and emerge wherever there is a gap in which the rosettes can grow and flower. Thus the leaves and flowers of the New Zealand hairbell may appear some distance from the actual root system. Several of the plants with which it grows natur-

ally have also adopted this device — most notably the snowberry (Gaultheria novae-zelan-diae) and the patotara (Leucopogon fraseri). These plants also defy most attempts to transplant them from the wild, but it is possible to succeed by treating them as cuttings. Seed of the snowberry usually germinates freely if it is fresh, but the seedlings are of excessively slow growth. The patotara sets goodlooking seeds in its attractive orange fruit, but these rarely, if ever, germinate in cultivation. The mechanism which enables patotara seeds to germinate in the wild is not at all well understood, and it may be that the seed has to pass through the gut of a bird. Or there may be some other, unknown, element.

All these factors in combination may explain why the hairbell, the snowberry, and the patotara have arrived by different routes at their common solution to the space problem.

As a horticultural entity, the New Zealand hairbell is at present largely confined to the gardens of those to whom New Zealand plants are an obsessive interest. It is not quite pretty enough to

compete on equal terms with its European equivalent, Campanula cochlearifolia.

Wahlenbergia trichogyna, with its large, sky blue flowers, is a more striking plant but its fugacious life-style lessens its garden value. To find the best of the southern hairbells you have to look to the Australians — wahlenbergia gloriosa, W. tasmanica, and W. ceracea.

The last is the pick of them. Above dense, green foliage mats it flaunts large, sky-blue, wide-open bells for months in summer.

The other two share the peripatetic habits of the New Zealand hairbell, indicating that they are colonising plants which like fresh soil from time to time. They tend to thrive in one place for a year, perhaps two, then die out, only to re-emerge elsewhere.

W. tasmanica has skyblue, thimble-sized flowers, with more substance than those of the New Zealand hairbell. Its tufts of small foliage are closer and glossier, too. W. gloriosa runs about and sends up short stems, rather than rosettes. Each shoot is crowned by large, open bells which are deep purple-blue.