With many rock plants a greater amount of care is needed in handling than is required by the inhabitants of the herbaceous border. An alpine house as an adjunct to the rock garden makes it possible to give them this extra care, and so toall kinds of rock plants.
A further use for an alpine house is in the winter culture of rare rock plants that will not stand our damp, foggy winters. It should be recognized by the rock gardener from the outset that the alpine house is not a warm house. It is not intended as a protection against frost, which rarely kills alpine plants, but as a protection against the damp air and rains which cannot be avoided in the open in this country.
Heating apparatus certainly exists in many alpine houses, but its purpose is to dry the atmosphere, and usually the cooler the house can be kept the healthier will be the plants.
BLOOMS THAT NEED GLASS SHELTER
Still another reason for cultivating certain alpines under glass is the delicacy of their blooms. Some plants flower when our weather is, generally, rather showery, and if we are to make certain of havingin perfection, glass shelter is necessary. In some cases, too, as with some of the rare saxifrages, the plants are grown in pans all the year round under glass, partly because of their real beauty and interest at all seasons.
The best alpine house is a span-roof type with rather low roof, so that the shelves, while showing off the plants well, are not too far removed from the glass. For the same reason
the shelves are usually on each side, allowing for a central path a cool staging is desirable, and this usually takes the form of al 2-in. Layer of pea-sized gravel.
Although good ventilation is absolutely essential, care must taken not to allow a draught through the alpine house, as plant&, that are used to the still air of the house suffer keenly in unaccustomed draughts. Strange as it may seem, when we think of the blazing sunshine on the high Alps, certain of the rare alpines do need a little shading in the hottest part of the year, and for these specimens whitewash over the glass is the simplest and most common method for protecting delicate growths against the direct rays of the sun„
CLEANING THE ALPINE HOUSE
Cleanliness is another important point in the general care of the alpine house. Fumigation is the only really safe method to adopt is ridding the house of various glasshouse pests, such as scale, insects and wood lice. The preparation of composts for use in the alpine house is also very important, and all soil used should be sterilized.
Fibrous loam, with some-mould and a good proportion of; gritty sand (i.e., sand that is fairly coarse, not fine sand which cakes almost as badly as clay in some circumstances) makes a good general , and a supply of stone chippings of various degrees of coarseness should also be to hand.
USE OF ALPINE PANS
Alpine pans are sold by all sundriesmen. These are like broad; flower, several inches deep, and raised a little from the saucer.1 Wide holes are provided, and in planting alpines for the alpine house these holes are first covered with about 2 in. of coarse,’ material. Broken crocks (i.e., 4-in. pieces of broken’ flower pot) with a few larger stones make a good drainage layer. The idea of this layer is that when the plants are to be watered, the pans can stand in water 2 or 3 in. deep, and the moisture will gradually percolate to the upper layer of soil.
In a great many cases the pans stand permanently in water, so that thecan always be kept supplied with enough moisture. The fact that the top soil is of a very open nature, that is, at least one-third sand, allows for the circulation of air to the roots, so that the growth remains healthy.
Inthe rare alpines for under-glass culture, the idiosyncrasies of each should be catered for, crushed mortar being given to the lime-loving saxifrages, and sandy peat provided for such plants, as the dwarf campanulas, and the rock daphne (D. rupestris). Special care should be taken over this.
A full list of rock plants suitable for the alpine house, with culture for each, would occupy a volume on its own; but here is a short list of a few subjects that the beginner might use to stock his shelves, adding to them from time to time as he becomes better acquainted with these interesting plants.