THE ROCK GARDEN AFTER SPRING

Otago Daily Times, Issue 23685, 17 December 1938, Page 26

THE ROCK GARDEN AFTER SPRING

TIDYING-UP THE STRAGGLERS HELPING LATER-FLOWERING PLANTS As spring passes into summer, the rock garden loses some of its early beauty, and, unless sterjs are taken to rid it of fading flowers and straggling growth, it may even become positively untidy. It behoves the gardener, therefore, to set abo* t a little ele&ning-up in good time. Such naturally trailing plants as aubrietias and arabis will benefit from a moderate cutting-back as soon as their flowers fade. This will encourage ba 1 growth, and prevent the plants from getting brown and bare at the centre. The work can be done very quickly with a pair of large scissors, or even, in the case of big clumps, with garden shears. Incidentally, some of the new shoots that the plants will make after this cutting back may, if desired, be detached when just under an inch In length, in the case of aubrietias, and a couple of inches long in the case of Arabis, and inserted as cuttings Thev will root freely enough in sandy soil in a shaded frame, or even outdoors in a shady position. Candytuft and Sun Roses Very similar remarks apply to the treatment of perennial candytuft after flowering. Although this does not exactly trail, it spreads rapidly in all directions, and may overgrow less vigorous plants, if not kept in check. In any case, the removal of faded flower heads to prevent seed formation is of double value, preventing untidiness and saving the plant the unnecessary strain on its vitality caused by producing seeds. Sun roses (helianthemums) definitely benefit from a moderate cutting back immediately after flowering. They should not be cut into hard wood, as this sometimes fails to produce new growth, but, if the younger shoots are shortened by anything from a third to threequarters of their length, the plants will make plenty of growth, and remain compact and attractive for years. Unpruned sun roses may become very bare after a time. Once they have got into this condition, it is difficult to renovate them. Alpine Violas A few plants, and notably alpine violas, will continue to flower almost throughout the summer, if the faded blooms are removed from time to time If it is desired to propagate these varieties, it is advisable to prevent a few plants from flowering for a time by cutting off all the buds, and shortening some of the older growths. They will then make young shoots from the base, in just the same way as aubrietias and arabis already referred to, and these may be taken as cuttings and rooted in sandy soil at any time during February and March. Top-dressing Pruning is not the only task in the rock garden at the moment. Topdressing is also important, especially in a dry season such as the present. Rock plants do not make great demands on the soil, so far as food is concerned, and they do not require chemical fertilisers, but an annual topdressing of a compost prepared with a little good loam, moss peat, or leaf mould, sharp sil-

ver sand, and stone chippings, can do nothing but good. It encourages the formation of fine roots, and, by preventing excessive surface evaporation, conserves the natural water reserves of the soil. Such topdressing should only be spread quite thinly, and must be worked right into the basal shoots with the fingers. It is of particular value in case of many late-flowering alpines, such as the autumn gentians, and will sometimes induce plants that have hitherto been barren to produce bloom. In the case of dwan heathers, mossy saxifrages, and violas, a more spongy compost will give better results than the gritty mixture recommended above. Moss peat may well form the bulk of it, with a little sharp sa. 1 ' keep it open, and some good fibrous loam to supply nourishment. An annual dressing- of this humus-, ich compost will go a long way towards preventing the central browning which so often disfigures mossy saxifrages if they pre neglected. Straggling shoots of heather may be laid flat on the ground, and covered with half an inch of the compost, when they will often form roots of their own.

It is quite a fascinating pastime to raise a few alpine? from seed which one has saved at home. There is no difficulty about this, if a few plants are set aside for seed bearing and-left untrimmed. Watch the seed vessels that form af'-r flowers fade, and as soon as they turn yellow and show the slightest sign of splitting open, cut them off carefully with as much stalk as possible, and lay them in small boxes, lined with clean white paper. Stand these in- a sunny window or greenhouse until they are thoroughly ripe and the seeds fall out readily, and then packet the seeds up, label them carefully, and put them away in a cool, dry place until the following spring. They can either be sown in a frame during March, or in May outdoors, where they are to flower. The former method is the better with really choice varieties, but most of the common alpines come readily enough from an outdoor sowing. A Choice Bellflower One beautiful late-flowering alpine for the rock garden is Campanula Zoysi. At its best, there is no more lovely plant at the end of the summer, and it smothers itself in attractive!', puckered flowers in a lovely shade of china-blue. Its one enemy is the common garden slug, which appears to be willing to face any dangers to enjoy its tenccr leaves. An occasional vatering on moist, sultry evenings with a solution of permanganate of potash in water, at' a strength of a level teaspoonful of crystals per gallon, will go a long way to keeping off these persistent foes; but, ♦ be on the safe side, it is advisable to place a zinc collar around each plant in good time. If these collars project a couple of. inches out of the soil, and completely encircle the plants, there is little danger of slugs surmounting them.