PROPAGATING ROCK PLANTS.

Otago Daily Times, Issue 20330, 11 February 1928, Page 3

PROPAGATING ROCK PLANTS.

A large number of rock plants can be propagated from cuttings in the summer, and the stock raised in this way is far superior to chance divisions, often very imperfectly rooted, made in the autumn. It is absolutely necessary to devote a cold frame to the work, for if put in theopen ground most of the cuttings would shrivel up before they became rooted. The frame should be stood in full light, but to save the cuttings from excessive heat it is best to place it so that it faces the north [south in New Zealand]. A good layer of ashes should be put in tho frame to serve a double purpose, provid ing the cuttings with a moist cool bottom, and ensuring their not being too far away from the glass. If the ashes come to within 6in or Sin of the glass, so mucli the better for the cuttings. After trying various methods I have found that the best plan is to put the cuttings in small pots, Sin or in diameter, rooting from four to eight cuttings in each. In some cases it is best to put the lesser number in a pot, and then plant them out in the autumn without separating them: but things that take up a fair amount of space can be rooted close together, and potted off into small pots when they start growing. _ The little pots should be well drained, and the best soil for general use is a mix ture of four parts light loam, one of leaf mould, and one of silver sand. Some plants that are peat lovers root better in peat and sand, and more coarse sand or rock chippings can be added for moraine subjects that do not care to have much soil around them. Adding a top layer'of dry sand just before putting in the cuttings greatly facilitates the rooting process. A cheerful optimist might advise keeping the frame moist and absolutely closed until the cuttings rooted, but experience teaches that it is better to give a little air night and day, and it will be enough to push the light down 2in. The cuttings should be watered as often as they need it, giving attention to eacli individual pot, missing those that ire already moist enough. One great point is to keep the. cuttings from flagging, and in hot dry weather it is’ advisable to spray them with soft water during the early morning and late afternoon. Even with a frame facing the north [south] there is a fear of getting too much sunshine, and a thin screen, such as a piece of tiffany or a mat, should be put over the glass during the brightest hours of a sunny day. A thin coat of whitewash can be used, but these little mountain plants are lovers of light and need all they can get on our cloudy days. The majority of the cuttings will root in three weeks, though others may take much longer, and when rooted they should gradually be given more air, out not fully exposed until they have been potted off and arc well rooted in the new soil. Some subjects that root freely from summer cuttings are achillea, sethionema, alyssum, aubrietia, cistus. erysimum, dianthus, dryas, crodium, geranium, helianthemnm, iberis, linnm, lithospermum, origanum, phlox, thymus, viola, veronica, and zauschneria. Fresh young growths of these from 2in to 3in long make excellent cuttings. It may oe well to mention that Lithospermum prostration and its variety Heavenly Blue are lime haters, and they only root freely in a soil devoid of lime, so it is best to treat them to a mixture of peat and sand. When dealing with saxifrages of the mossy kind it is best to dibble tUree or four rosettes in one pot for planting out in tho autumn without disturbance. A pocket filled in this way will be one mass of bloom the next season. New rosettes can be taken off the encrusted saxifrages, the larger ones being given single pots and the smaller ones put in three or four together. The cushion saxifrages should not he interfered with durifig summer, for it is best to divide

them Just after they have flowered in spring or during the early autumn. Pieces can usually be got from them with roots dlerady formed, and they can go back ,n the moraine or a pocket.

"The smaller tufted androsaces are tod tiny to be turned into cuttings and can bo divided in the autumn, though it is sometimes possible with large plants m hand to pull off sprays and root them in the cold frame. Larger varieties making runners, after the manner of A. sarmentosa, can have the runners taken off and inserted as cuttings, getting the soil right up to the lower leaves. That gem of summer flowers A. lanuginosa, will root freely if the voimg growths are put in as recommended for ordinary things. It is the safest plan to keep the young plants in the frame during the "winter, for, though they are cold proof, they do not like the damp of our winters. Tilings that increase with great rapidity, such as the ledums and sempervivums usually give a sufficient stock by division in the autumn; but choice or rare varieties can have little pieces taken from them, to be pricked off in pots like cuttings.—T. H. World, in the Garden.