Alpines for the Rock Garden
ALPINES are among the most exciting .of plants, having the fascination of intricate embroidery — and their delicate detail, exquisite form and brilliant colours are combined with the wonder of the miniature.
They are at home in mountainous regions’, and so will tolerate thin stony soils and drying winds.
Many of them are easy to grow provided their natural conditions of sharp drainage are imitated for them. As well as in thethey can be grown in a raised bed or along the top of a low wall in a , in a trough or sink garden, or anywhere where their beauty can be looked upon from above.
There is something very personal about a rock garden, and there is no better way of becoming well acquainted with its innumerable small inhabitants than by giving it the close attention it needs, and which it so well repays. It does not take an undue amount of time and trouble provided it is properly looked after, but if it is neglected it is more difficult to put into good order again than other parts of the garden.
A rock garden that has become over-grown with such possessive plants as snow-in-summer (Cerastium tomentosum), the lovely but invasive creeping( ), or in which such as couch-grass, running thistle or bindweed have been allowed to secure a firm hold, will be difficult to clean and much of the stonework may have to be removed and the garden rebuilt.
Before building a rock garden remove allfrom the site, and see that the is free from potential troublemakers. Extreme precautions would involve the use of sterilized soil in which weed-seeds and pests such as wireworms, leather jackets and other harmful grubs have been destroyed. But it would be expensive if sterilized soil were purchased, or laborious if the soil were sterilized on the site. And in any case, sterilization is only a temporary safeguard, as seeds will inevitably blow in from surrounding areas, and omnivorous grubs will find their way into tender roots and succulent shoots.
WHAT NOT TO PLANT
Much trouble can be caused through an unwise choice of plants. Many fast-growing and invasive plants are very decorative and showy, but they should be avoided in the early and inexperienced stages of rock gardening, or used with extreme discretion until their potentialities are fully appreciated and suitable positions can be assigned to them.
The following plants should be regarded as probable troublemakers, certain to occupy too much territory too quickly and likely to smother less vigorous neighbours: Acaenas of all kinds,tomentosa, ajugas of all kinds, Allium moly, — single or double flowered, Campanula poscharskyana, Cerastium tomentosum, cotulasof all kinds, Helichrysum bellidioides, hieraciums of all kinds, Oxalis corniculata — a pestiferous weed, never to be admitted, and Veronica filiformis.
Plant the rock garden in either spring or autumn, as there is little to choose between these two seasons.
Most alpine plants are grown in pots and are supplied in them by the nurseryman, and can therefore be safely planted out over a much longer period than other plants. But if they are planted well out of either of the two recognized planting seasons they will need extra care and attention, both with regard to watering and to shade, until they are established.
A rock garden planted in the autumn is unlikely to require much watering after the initial soaking unless the weather is unusually dry for periods of more than a week at a time, when it will need a weekly soaking until the plants are sufficiently established to seek their own moisture.
But spring planting necessitates more attention to regular watering.
A mulch of fine grit or gravel spread half an inch deep over the entire rock garden is much appreciated by the plants and, as it conserves the moisture in the soil beneath, is a labour-saver.
Apply this layer after planting and renew periodically. Work the grit right under the plants so that their collars are surrounded by it.
The grit discourages slugs, whichin the cover of a plant, and keeps the neck of the plant free from wet soil, which could cause decay.
The mulch of grit will help to prevent plants being heaved up by frost and left with exposed roots, but plants set out in the autumn are unlikely to achieve a really firm root-hold before the winter, and may be ‘lifted’ by frost. If this happens carefully press them back into the soil as soon as the ground has thawed and is no longer saturated.
RAIN AND WIND
Plants with very soft, hairy leaves which persist through the winter may need slight protection during very wet periods, so provide this by placing a small piece of glass over them, secured by wire clips.
Drifting leaves from deciduous trees can also be a danger, as they often pile up in a corner between rocks, and distress plants which have to endure this soggy blanket. Remove them at intervals, and, after high winds, watch carefully for leaves which may have drifted in from quite far afield.
Perennial plants that make a lot of soft growth, such as aubrietas, alyssums, arabises, helianthemums and saponarias, should be cut back quite hard when they have finished flowering. This applies particularly to aubrietas, which soon grow into leggy, untidy mats and flower less profusely if they are not given an annual trim, and helianthemums, which last for years if properly tended, but which may perish in two or three years if left to straggle into loose bushes.
Never let weeds get a strong hold on any part of the rock garden. A sturdy tuft of grass is a bad neighbour for a small alpine plant, and it may be impossible to remove the weed without uprooting the plant as well.
It does not take long to work over a small rock garden, scuffing and loosening the soil with an appropriate instrument, such as a small hoe, and it this is done regularly weeds will never become a problem.
Slugs are a grave menace to spring-flowering alpines, as they like to eat the new leaves, flower stems and buds. They shelter beneath overhanging plants and in crannies between stones.
An occasional inspection of these likely hiding places, and keeping the plants clean and free from weeds, will keep the slugs down to a minimum. An application of one of the several effective slug killers will deal with any which escape notice.
Woodlice also can cause much damage, so sprinkle D.D.T. Dust in areas where they are troublesome.
Greenfly rarely attack alpine plants, but if any are found in the rock garden use one of the systemic insecticides, carefully following the instructions on the container.