This section is from the book "The Gardener V1", by William Thomson. Also available from Amazon: The New Organic Grower: A Master's Manual of Tools and Techniques for the Home and Market Gardener.
IN compliance with the request of one of your correspondents, who desires a chapter on Allamandas, I beg to offer the following remarks, in the hope that he may derive some assistance therefrom.
The Allamanda, without question, is one of the most splendid stove-plants we have, whether as regards the beauty of its flowers, or the length of time over which some of the species produce blossoms without interruption. The varieties A. cathartica and A. nerifolia very much resemble each other both in flower and habit, partaking more of what may be termed the style of a bush, under particular treatment. Then again, A. Hendersonii and A. nobilis are better fitted to cover a rafter, or for winding spirally around a set of stakes when grown in pots for specimens. "With these differences in view, we shall proceed to discuss a few of the different methods of treatment, commencing with propagation. Perhaps early in March is the best period to make the cuttings from the young growths. The points of these, when about three joints, strike freely, inserted under a bell-glass, amongst soil composed of well-reduced leaf-mould and silver-sand in equal proportions. The bottom temperature into which the pots ought to be plunged should be kept at 70°, with the atmosphere at 65° to 70°. Light shading should be resorted to in bright sunshine, until the cuttings have absorbed sap sufficient to sustain themselves erect under the influence of the sun, when shading ought to be dispensed with, unless when the sun is extra strong.
Pot the plants when rooted into separate pots, retaining as much soil as will adhere to the roots, so that the plants exhibit no signs of suffering by the change. The soil which we prefer is composed of rich, moderately light, turfy loam two parts, one part equal portions of sharp sand and old leaf-mould, and the other part old Mushroom manure. These ingredients, well incorporated, form an excellent compost for this and all the subsequent pottings required. Pots from 3 to 4 inches diameter should be used in the first instance; these will afford ample room for the bulbs and roots without breaking. Allow plenty of broken pots, to secure ready drainage, and pot with the finer parts of the soil. After potting, return the plants to heat again, and water sufficiently to moisten the whole soil. Shade, and maintain heat and moisture about the plants to accelerate growth. Pinch out the centre of each plant at the first indication of active growth, so that laterals may be obtained; and those laterals, when long enough, should be trained separately into uniform distances, to make a nice foundation for specimens, or indeed for climbing purposes as well.
Pots two sizes larger should be supplied on every occasion of shifting, while the crocks ought also to be covered by the turfy lumps of the compost to keep the drainage clear. Continue by those means to keep the plants in active growth, syringing overhead mornings and evenings in hot, dry weather, along with abundance of air. Pinch again when the first set of growths have produced laterals 6 inches long, and allow all the other succeeding growths to grow without pinching - all the attendance necessary after this being comprised in training the growths neatly as they make progress, and affording larger shifts when the condition of the roots demand such. Flowers may sparingly appear on some of the points as they ripen, but those, as a rule, are few in number at this stage of growth - the next set of wood produced the following summer being the flower-producing portion of the wood.
Passing onwards to September, we will find, should all have prospered,' the plants mostly occupying 10-inch pots, with splendid heads of wood and foliage. At the same time indications of exhaustion will be exhibited, the plants are approaching ripeness, and will require to be cautiously dealt with, to preserve the roots and harden the wood, by in a great measure withholding water until the succeeding February, when preparations for fresh growth ought to be attended to. Meantime stand the plants in a dry airy place in the stove, where no opportunity is afforded for them rooting beyond the pots. Wintered in this manner, with only enough of water given to keep the foliage from flagging, they will be in admirable condition to suit the desired end.
Early in February turn out their balls and reduce the same, taking care to preserve all the fresh roots while separating as many as possible. Repot into pots of 12 inches diameter, and while in the act of potting, press the compost unusually firm about the roots. Then supply tepid water copiously, so that the soil is thoroughly penetrated. Plunge for some time following this in smart bottom-heat, that fresh roots and growth may be produced, after which the plants may occupy a place on the stage fully exposed to the sun. Tie in the shoots as they advance, with an eye to harmony and neatness of plant. And in the course of summer these shoots will furnish bloom, and continue to keep up a succession on some of the varieties to the end of October following. Finally, when it is fully ascertained that flowers are in formation, add to their water a small portion of guano. Never once allow the plants to get dry at the roots, nor permit shade to affect the plants, else the flowers will droop half developed. Either strong shade or insufficiency of water at this period or stage is sure to have that effect. As the winter again approaches, manage as recommended for the winter preceding, - and so on.