Late developers prolong rock garden colour

Press, 4 December 1981, Page 8

Late developers prolong rock garden colour

Gardener’s W DIARY

Derrick Rooney

October, say the experts, is the month of the rock garden — that is when the trickle of tiny treasures becomes a flood, and blazes of colour erupt on all sides. To a degree they are right, because alpines evolved in harsh climates, and typically will burst into flower and seed almost overnight once the weather is right, then retire for the rest of the year. But there are a few that flower on and on through the summer, and some precious latecomers that help to provide a succession of colour up to Christmas and beyond, until it ■is time for autumn bulbs. I thought it might be interesting to list some that were at their peak last week. Pride of spectacular place went to a large spike of Saxifraga cotyledon, a plant raised from seed three years ago and flowering for the first time. The leafy rosette is not large, just 20cm across and 6cm high, but the inflorescence that springs from it is a giant among the pygmies. I have just measured it — it is 60cm high and 40cm wide, branching right from the base, a solid cone of glistening white. A second spike just emerging from the rosette will prolong the display perhaps until Christmas, but will not be as big. This saxifrage is a very widely distributed species in Europe and North America, and there are a number of geographical forms, which have been grouped in two broad types — “genuina” from more northerly latitudes which has larger leaves and a smaller inflorescence, and “pyramidalis” from southern Europe which has a bigger inflorescence and smaller leaves. Once there were many species, but now there is just the one, with its two divisions; my plant belongs in the second. It is not particularly rare — you might even call it a bread-and-butter alpine — but it is choice. Growing alongside it is another, very different, saxifrage raised from the 1978 seed sowing and also flowering for the first time. This is rare. It is Saxifraga vayredeana. Unlike S. cotyledon, which has hard, strap-shaped leaves with teeth and encrustations of lime on the margins, it has mossy light green foliage and is making a dense, twiggy hummock beside a path.

In the wild this species is found only in the Montseny Mountains, near Barcelona. There is nothing spectacular about it, but it has charm. The flowers are small, and creamy white, and there are several on every stem; once it gets going so'many stems are produced as to hide the plant. In a monograph on saxifrages published in Britain it is treated as an alpine-house plant, but here it grows quite happily in the open, in a coolish spot which gets morning sun only. The leaves are distinctive, being stemless and shaped like a knifeblade but bent back and split in three segments at the apex; once seen, they could hardly be confused with any other species. Other choice latecomers in the same part of the rock garden include Roscoea humeana, Primula viali, Celmisia dallii, and Calceolaria “John Innes.’’ The roscoea is not only first on the list but is of the most singular appearance — there are no leaves yet, and the flower, rich pinkish purple with contrasting white eye and yellow anthers, is just clear of the ground. In about 10 days the flowers will have faded away and the pleated green leaves will be lengthening, like little sheaves of sweetcorn. These will grow for a while, but before autumn comes they, too, will fade away, not to be seen until summer comes again. Roscoeas belong to the ginger family, Zingiberaceae, a mostly tropical group of which they are rare tem-perate-zone examples. The flowers are remarkable — hooded, with a flaring lower petal and secondary ones which hang down like goatdrops; imagine a cross between an iris and an orchid and you have a roscoea. They are not very easy to

grow, because they are very exacting in their requirements — they need a humusy, gritty soil, with their heads in sun (for the mornings, at least) and their feet in the shade, and throughout the growing season they demand plenty of moisture. But at the same time they must have very sharp drainage. Roscoea humeana, which has the largest flowers on the shortest stems, is probably the most spectacular, but there are others which are good, and a couple of tall ones that will grow in the herbaceous border, given appropriate soil. These are R. purpurea,

which flowers after the leaves have developed, and R. procera, a little larger and a little better. There is a yellow species, R. cautliodes, which I have not yet acquired. Another, sometimes offered by nurseries, is R. alpina, which is reputedly the easiest to grow but the least satisfactory because the leaves emerge before the flowers, which are small and tend to be hidden. I flowered it last year, and it wasn’t bad, because the leaves were reduced by drought and the flowers were easy to see. But this year it has not come up again. I am not worried, yet — I have known

roscoeas to stay dormant until January, and even to take a whole year off. Primula viali. one of the alpine plants that every enthusiast must have, is an odd man out in .its family because the flowers, instead of growing in conventional primula fashion in whorls, are in narrow spikes like red-hot pokers. The spikes are bicoloured, rich carmine buds opening to rosy lavender. Most catalogues put out by alpine nurseries list it among the moisture-loving primulas, but unlike some Asiatic species it doesn’t seem to demand constant moisture as long as there is plenty of humus in the soil. After it had flowered through a dry spell last year I looked up the proceedings of the 1928 RHS primula conference, and learned from a report on the natural habitats of Chinese primulas by Dr H. Handel-Mazetti of the Vienna Natural History Museum that it is basically a plant of wet meadows. But, reported the doctor "it is very eurytopic, enters the most varied thickets, even the dense and dwarf evergreen bush of prickly oaks. and dry stony meadows." ’ “Eurytopic” doesn’t appear in my Oxford dictionary but I imagine it means adaptable. I wouldn’t risk Primula viali in too dry a place, though - its happy compromise home that I have given it is at the bottom of the rock garden, with plenty of gravel round its crown. All the water drains off on to it in summer, and in winter the gravel overcoat keeps its crown snug and dry, which is important. Like many Chinese primulas it disappears below ground in winter, and is a late riser in spring — often it shows no sign of growth until the beginning of November. Calceolaria “John Innes” is a hybrid which bears the

name of a famous English horticultural research station, and is a graceful miniature version of the great gross hybrid calceolarias sold as indoor plants. I believe the fabulous Calceolaria darwinii is in the parentage. but unlike darwinii, which is next to impossible in Canterbury, "John Innes" is very easily grown. It is very hardy. Like Primula viali it makes a thorough job of disappearing underground in winter, and it does not reemerge until summer. Once it gets through the ground, though, it shoots up into flower quite quickly. One of its popular names is “lady’s slipper.” but the lady must have been a very-heavy-footed model, because each flower has a great protruding bulbous bow. The whole flower is closed in all round, like a pouch, and the only ingress is a small slit at the top. It is such an unlikely shape that I can only speculate that it was designed to be attended by a similarly unlikely insect. The colour is golden yellow, speckled with red. Last but not least on this week’s short list of late treasures is Celmisia dallii, a native mountain daisy from western Nelson. It is not very common in cultivation and has a reputation for difficulty, but is behaving so kindly in my garden that the reputation must be replaced. Without hesitation, I would place Celmisia dallii in front rank of both flowering and foliage plants in the rock garden. The leaves are not very big, only 10cm to 15cm long when fully grown, but are densely coated with silver or buff down, and thus have the air of distinction peculiar to silver plants. The flowers are handsome, too: silvery pineapple-like buds burst open to reveal a brilliant whiteness which contrasts stunningly with the science-fiction flowers of the calceolaria alongside.