Summer flowers for the rock garden

Press, 17 December 1982, Page 10

Summer flowers for the rock garden

Country Diary

Derrick Rooney

Campanulas, one of the summer mainstays of the rock garden, are absent from the New Zealand flora.

But the family has its equivalent in the various species of wahlenbergia, ranging from the very rare (wahlenbergia trichogyna, from one site in Marlborough) to the übiquitous New Zealand hairbell, wahlenbergia albo-margin-ata, which is in flower now throughout the high country. This little plant is seldom seen in cultivation, blit it is well worthy of cultivation in the rock garden — it is one of our daintiest alpines. And as it comes from moderate to low altitudes, it is fairly easy to grow. Clumps from the wild do not transplant readily, but plants are easily raised from the seed which will be ripe in a few weeks.

Wahlenbergias are found in Australia also, and three fine species from the transTasman mountains which pop up occasionally in nurserymen’s lists are w. gloriosa, tasmanica, and ceracea.

The last is the pick of them — above dense, green mats of foliage it flaunts enormous, sky-blue, wideopen bells. Flowering continues for a long period in summer. The other two sucker and run about a bit, indicating that they. are colonising plants. They tend to thrive in one place for a year or two, then die out, only to reemerge elsewhere. Tasmanica has sky-blue thimbles, and gloriosa has

bigger, more open bells, in deep purple-blue. Neither likes to be overgrown by taller plants, though both will come’-up underneath prostrate shrubs, where they get a cool rootrun.

In the Northern Hemisphere the wahlenbergias disappear from the campanula substitutes, to be replaced by symphandra, adenophora, and codonpsis, three genera which are, or should be, keenly sought grist to the alpine gardener’s mill. . Symphandra wanneri is one of the best — on a plant of low stature dangling bells, each with the end neatly sliced off as though with a giant razor blade, appear in early summer. The colour is rich, deep, violet blue. Unfortunately this lovely plant is monocarpic — it dies after flowering. It is supposed to leave a legacy of self-sown seedlings but with me has not, so far, done so. There hasn’t even been any seed to save and sow in a pot. Symphandra armena is another good one which forms a bushy little plant upwards of 30cm high, and smothers itself in summer under a cloud of pale blue bells. It, too, dies after flowering. I now have, however, a plant given to me as “symphandra armena — perennial form” which is at present a mist of dainty, pale mauveblue bells with turned-back lips. In winter it dies back to a dense, green hummock. Every visitor in the last three weeks has admired it, but I. haven’t been able to

species, and has gone into a border, though it is not too tall for a large rock garden. This is reputedly perennial, and it has grown a large, carrot-like white root that looks permanent. The only reference to this species that I have been able

tell any of them its name, and none of them has been able to tell me. Still to flower is adenophora hoffmanii which, if the seed was true to name, will have many graceful, dangling cream bells. This is a slightly larger

to find made no mention of the flowering time but the plant is behaving like a latesummer flowerer. The beginnings of a flower spike are already visible. Still later to show signs of flowering is the tiny adenophora tashiroi var. homozana. This is a choice rarity which grows wild only on the Japanese mountain from which it took its varietal name.

Possibly it is the slowestgrowing member of the family — my two-year-old plants are only a few centimetres high. In autumn, an unusual time for an alpine to flower, it will carry large purple-blue bells. Among the true campanulas flowering now are the lovely cream c. alliarfifolia

— a little too tall for the rock garden, but placed there, regardless — and the prostrate c. bestulaefolia, which was supposed to be monocarpic but is in its third year and going strongly. It has dull green, hardish leaves shaped and notched like those of the silver birch trees, hence the name. The flowers are long, narrow bells which vary in colour from pink to white. My plant has white bells. The species of codonopsis are mainly Himalayan plants closely related to the campanulas. Some are tufted, some will climb to waist height through thin scrub; most have fleshy or tuberous roots to which the plants die back every autumn, so that they disappear beneath the ground. The attraction of this

genus is the extraordinary array of interior markings on the flowers of many species. Codonopsis clematidea. one of the twiners, is my pick of the bunch. It is flowering now, bearing tubby pale blue bells that look, from the path, rather nondescript. But tip up a flower and you will see inside the richly coloured concentric markings in lavender, mauve, orange and cobalt blue. Codonopsis ovata, which has finished flowering, is synonymous with the former species, according to the reference books, but is definitely 7 different in the garden. The interior markings are similar, perhaps not quite so rich in c.. ovata. The latter flowers several weeks earlier, and whereas c. clematidea has tubby bells with reflexed lips, c. ovata has .■■ straight-sided bells, opening wider. Both species are described

as natural twiners, but I have them in the open rock garden, where they stand without staking. C. clematidea is the taller. Yet to . flower is c. cardiophylla which has. as the name indicates, hearUshaped leaves. I have only the one plant which came up from a packet of seed, and it is now in its second year and growing away strongly, though as ' yet there is no sign of flowers. The roots are tuberous. A species which I have not yet grown, but will grow if I ever see it catalogued, is codonopsis meleagris. This is rather like c. clematidea. but the markings are richer — they are heavily laced with chocolate, rather like a fritillaria. Some of the species in this genus are very tricky to grow. They mostly germinate like mustard and cress, but damp off just as rapidly if not handled very carefully — the young seedlings like plenty of moisture at the roots, but cannot abide standing in the stagnant, moist air in an ill-ventilated frame or shade-house. They dislike disturbance when young, also, and losses at the pricking-out stage . tend to be heavy. Once you get them through the first winter, however, they seem to become fairly permanent, though I did lose unflowered plants of several species in the wet 1978 winter. These included the rarish . codonopsis mollis, and one or two others. Subsequently I ■ have been unable to get more seed.