The Alpine Greenhouse

A good example of the simplest form of the unheated greenhouse is to be found in the Alpine House at Kew. It is nothing more than a low span-roofed glass-house, 40 ft. long by 9 ft. wide, with flat stages on each side of a narrow gangway, and has no heating apparatus of any kind. It is provided, however, with shading to temper sun-heat, should it prove too powerful, as it often does, in early spring. Here, throughout the winter and spring months, a succession of low-growing plants and bulbs indigenous to the alpine districts of all parts of the globe may be seen in happier circumstances and in better flower than would be possible out of doors in our changeful climate.

A large proportion of such plants perfect their growth rapidly during the short but strong summer heat of their native habitats, and are almost ready to burst into flower again when their progress is arrested, sometimes quite early in autumn, by a thick fall of snow which tucks them up safely for their long winter sleep.

Months later, when the snows melt and there is no more danger to fear, they have little more to do than to open their bright eyes upon the world new-clad in greenery. Any one who has had experience, for example, of a Canadian spring, will understand the sudden transformation from the winter shroud of snow to gay, green woods and plains enamelled with flowers.

Transplant the denizens of such climates to our seagirt Britain and, so far from being happier, they are sore bewildered and tried beyond endurance by the alternations of mildness and rigour to which they are subjected, and we who try to cultivate rare and beautiful species under these altered conditions too often meet with disappointment.

Under the protection of a simple glass roof, however, the want of the snow coverlet is not so much felt, and such plants can go on, without check from wind or weather, to perfect their pure, stainless flowers. At the same time, they do not give us that sense of unnatural forcing which is inseparable from the hardy spring-flowering shrubs, like Lilac or Wistaria, when, as is often done, they are brought on quickly into bloom in a heated atmosphere.

True alpine plants will not stand artificial heat, and the Saxifrages, Soldanellas, Cyclamens, Irises, and other mountain plants shown in the Alpine House at Kew are grown out of doors during the summer and autumn, either in prepared beds or in cold frames where they can be planted or plunged according to their requirements, and are brought inside to open their flowers. They are mainly grown in pans and pots which can be easily returned to their growing-quarters as soon as their beauty is past. Ice has been standing on several occasions on a small glass tank containing Azolla filiculoides in the Alpine House when I have seen Saxifraga burseriana major, Corbularia monophylla, Primula megasexfolia, &c., in flower, and many other plants in bud without showing the least sign of distress.

Saxifrages are typical plants for the alpine house. The earliest of them all to open is S. burseriana major, and any one may be proud of having, early in January, a well-established pan of so lovely a plant in bloom, for it takes some time to build up and some care to preserve in good condition.

Few gardens possess a superabundance of this fine variety or even of the typical species with smaller flowers which open a little later. Saxifrages, and especially these slow-growing, densely tufted species, do well grown in pans from 6 in. to 8 in. across, in light sharp soil freely intermingled with nodules of stone-some of the larger pieces being only half-sunk beneath the surface, against which the little tufts can nestle.

A very pretty specimen may be grown in such a miniature rockery. To increase the stock, when a plant has gone out of flower, a rosette may be snipped off here and there wherever it will be least missed, pressing it gently into a pinch of sharp sand on the surface of the soil. These will soon root, and each will become the nucleus of a healthy tuft.

Saxifrages of this section will live in the same pan for a length of time, the bare worn-out pieces being carefully cut away and fresh soil of the nature of pulverised granite added as a surface dressing, but much disturbance of the roots is to be avoided. Very many species of these minute silvery rock-foils may be grown in this way. The mossy kinds, represented by S. camposi, grow much more quickly into good specimens. Amongst the alpine Saxifrages may be found golden-yellow, pale primrose, purple, and pink flowered species, as well as white. S. cotyledon -S. pyramidalis and S. nepalensis being only fine varieties of the same-which belongs to the encrusted section, makes a noble pot plant in late spring, though few people, for some reason, succeed in growing it well.

To form a good specimen, perfect rosettes of the strap-shaped leaves must be chosen for potting singly in three-inch pots-" perfect" being said advisedly, as an ill-shaped rosette never produces a fine spike of bloom. These must be kept entirely free from the numberless offsets by which, in its native home, it creeps along the fissures of the rocks.

By giving frequent and gradual shifts into larger pots, the plants are encouraged to grow as large as possible before the flowering stems are produced. This may happen either in the second or third season, but if a succession of young plants be kept up by putting in sufficient offsets every year, some are sure to flower every spring, and the tall pyramid of multitudes of milk-white flowers, sometimes two and even three feet in height, is extremely ornamental. By planting several of the rosettes in a pan, thus restricting root-room, and taking care still to remove all offsets, a dwart specimen may be grown, carrying several feathery white plumes instead of the single pyramid.

No more truly alpine plant can be named than that child of the snowdrift, Soldanella. Its cultivation is not altogether easy, and a hint given by M. Correvon, years ago, having proved of great value, may be passed on to others. Soldanellas enjoy nothing so much, under abnormal conditions, as growing in living sphagnum, in full sunshine. Living sphagnum must, of course, be constantly moist, and requires a thin layer of sandy bog-soil at the bottom of the pan.

The tiny plants of Soldanella inserted over the surface of the moss send down their roots among the cool spongy stems and thrive apace. This method provides as good a substitute for the melting snow as can be devised under cultivation, but they are successfully flowered at Kew under ordinary treatment in pans of suitable soil.

To turn to an entirely different class of plant. Amongst the luxuries of the alpine house, at present, must be counted the newer species, increasing in number year by year, of dwarf bulbous Iris. Some of these are far from new, since I. persica, nearly related to some of these more recent introductions, is the very first plant figured in the old series of the Botanical Magazine (A.D. 1793). But of late years, collectors in various parts of Asia Minor have turned their attention to this beautiful genus, and our gardens will be richer in future by their labours.

Very many of these new species are tempting items for the Iris connoisseur. I. Heldreichi, with large grey-blue flowers and deep violet falls, is one of the most attractive of plants to grow for an alpine house. Not quite so striking, perhaps, in flower, but more so as a plant, with its abundant channelled leaves, is I. sindjarensis, a Mesopotamian species, which blooms in February and March, when its tender slate-blue flowers shading off to creamy white are both pretty and fragrant. In the same category with these rare species are I. Hausknechtii, I. Tawei, I. bolleana, and others.

Their culture is scarcely to be taken in hand by a novice, because they are both scarce and dear, and their requirements may not as yet be entirely understood, but there are others, like I. alata, I. orchioides, I. Danfordioc, I. bakeriana, &c., which are more easily procured, and are charming additions to the alpine house. Better known still is I. reticulata in its many delightful forms.

No more fascinating branch of garden work could, in fact, be taken up by the enthusiastic amateur than the furnishing of an alpine house for six months of the year from November till May, providing occupation for the summer and enjoyment for the winter. The form of it, besides, may be varied, for another arrangement which can be adopted for the alpine house is a permanent rock garden under glass-the lights being so put together that they may be entirely removed during the summer.

Evergreen ferns of low stature, some of the dwarf vacciniums and gaultheria, and other suitable greenery might here be grouped-intervening spaces being left with a view to the introduction of plants in flower in their season from the outside frames.

Such an alpine house, which may be larger or smaller according to circumstances, would make as charming a winter garden as could well be devised.
Alpine plants are legion, and it is impossible here to do more than indicate the lines upon which they may be used under glass, but a list will be found of the best and most suitable species, including many of the smaller bulbs and tubers which have been successfully grown at Kew and elsewhere for this purpose.

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