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.
Seldom are these plants grown for a display of their rich golden flowers during the declining months of autumn and winter. Generally they are to be seen in great profusion through the summer months, when flower-shows abound, and are therefore largely cultivated by exhibitors of flowering plants. These growers, in the majority of cases, have their plants in good condition; but in many gardens where plants are not grown for exhibition purposes, it is difficult to find much attention paid to Allamandas - in fact they are not generally well cultivated. However profusely flowered and beautiful they may appear when trained upon balloon trellises and staged for exhibition, they cannot compete, when thus grown and trained, either for effectiveness or beauty, with those grown as climbers under the roof of a plant-stove. When well grown in this position, they by far surpass any other plant I have ever seen employed for the same purpose.
If the house in which Allamandas are grown is rather lofty, so much the better, as the plants can be allowed to hang some of their shoots down from the wire-work to which they are trained, and thus present a more natural effect. If the house is not sufficiently lofty to allow the growths to suspend from the roof, they will not look stiff if trained to upright wires. The flower-shoots will grow fully 2 feet in length and hang beneath the roof, thus presenting a natural rather than a stiff appearance. Those who have never seen the roof of a house literally covered with A. Wardleyana (Hendersonii) cannot form any idea of the gorgeous and pleasing effect they produce.
Only a poor conception can be formed of the capabilities of this plant to produce a striking picture, when grown and trained upon a 4 or 5 feet trellis.
Allamandas bloom fully eight months out of the twelve, and a solitary plant, if well and judiciously-grown, will produce flowers over that period of time. With about three plants, started at different times, it is not difficult to obtain a supply all the year round. If a plant commences flowering in May, it will go on producing blooms until after Christmas; and if started a month or two later, it will of course flower until February or March. One important point to be considered is - those plants intended to bloom through the dark days of winter should not be allowed to commence blooming too early in the season. They appear to become exhausted in producing quantities of flowers in much less time during the sunless days of our winter than is the case during summer; and those that wish to achieve success should make provision for this.
Some may suppose the flowers of Allamandas are of but little service for cutting, except the entire stem bearing the flowers is severed from the plant; but they are invaluable, especially during autumn and winter. Here the single flowers only are removed, with no wood attached, and we pack hundreds in course of the season, and find they travel well. For low dishes or vases, these flowers are graced with a few fronds of Maidenhair Fern, intermixed with a few sprays of any other flower that will contrast well and rise out lightly from the ground of yellow.
Allamandas are easily propagated by means of cuttings at any season of the year when young growing shoots can be obtained. If rooted at once, a good and early start can be made the following year. They should be inserted singly in small pots, and if plunged into bottom-heat will quickly throw out a number of roots. When the roots reach the sides of the pots they should be transferred into others, 6 inches in diameter, and the one shoot allowed to extend until it reaches the height where the roof commences. The young shoot should then be pinched, in order to cause it to make two, which should be allowed to extend in an upright direction until the end of the season. They must be transferred into larger pots as they require it, until placed in 10-inch ones, which are large enough for the first year. The young plants will, if properly attended to, produce a few flowers during the season, and make plants as strong as ordinary pot-Vines will do in a season from eyes.
When the wood is well ripened, the plants must be brought to a standstill and rested for a time, and then cut back, leaving each shoot fully a yard in length. The shoots should be laid horizontally at the base of the roof, after placing the plants in 12-inch pots. By this means the shoots left will break growths from nearly every eye, which should be trained upright, except the extreme shoot at either end, which should be allowed to run in a horizontal direction as far as it is thought prudent to prune the plant back to the following year. If run about a yard on each side, and then allowed to go upright, the foundation is laid the second season for a plant to furnish a space of four yards of roof. The plants can be extended on this principle until they fill the whole of one side of the house, or as far as it is necessary to extend them. I filled the side of a span-roofed house, 40 feet long, with three plants, the third season from striking the cuttings. Two plants now occupy the space on each side of the house : one would have covered it before now, but two are preferable if a continuous supply of bloom is required. One plant can be retarded while the other is pushed forward.
By this system the house will not present such a grand display as if the whole was literally covered with bloom at one time. This is a matter for individual cultivators to determine, according to their taste and circumstances.
The soil most suitable for Allamandas is rich loam, with a seventh of manure or small bone-dust, and sufficient sand to make the whole porous; they require a rich soil to grow them well. In potting, the pots should be well drained; the drainage being covered with a layer of rotten manure before placing in any of the compost, which must be pressed firmly into the pots. Allamandas require potting as firm as it is possible, which causes the wood to be short-jointed, and the quantity of bloom greater than if loosely potted. When the plants are young, and are being grown on, they can be potted from time to time without reducing the old ball. But when in pots sufficiently large, and it is not necessary to increase the size, the ball can be reduced to one-half, and placed back again into the same size of pot. When placing plants in the same pots, sufficient room is left for a good mulching of cow or other manure, when the pots are well filled with roots. This assists the plants greatly, and the roots quickly lay hold of it. It is wonderful what a large amount of growth Allamandas will make in a 20-inch pot.
This size would be large enough for a plant to grow in to cover the side of a house 40 feet long, and have a distance to travel of 16 feet or more up the roof of the house, and produce thousands of large blooms.
While growing, these plants require liberal supplies of water. At first, after potting especially, when the roots have been considerably reduced, they must be carefully watered, giving more as they develop in growth. When they have to cover such a large space as alluded to above, they will require, during hot weather, water at least three times a-day. When the pots are full of roots, and have been top-dressed, manure-water must be freely given every time the plants are watered, or the blooms soon diminish in size. Soot-water every alternate watering is very beneficial to them : not only does it keep the foliage a fine dark hue, but adds brilliancy to the flowers. Water must gradually be withheld as the season for resting the plants advarices, and while at rest they need no water. After resting, the balls must be thoroughly soaked in tepid water in a tank, and be allowed to drain well before potting.
In bringing Allamandas to rest, the wood is generally well ripened at the bottom if pruned as I shall describe. When the plants have finished blooming and have been sparingly watered for about a week, they are allowed to go dry until the foliage flags, then a little water is given, but not sufficient to thoroughly soak them. If they are well checked at the first attempt they are soon brought to rest, and no harm results from the sudden change if the wood is quite ripe. After this, sufficient water only is given to keep the wood from shrivelling. The plants are then partially pruned back, cutting away all the unripe wood; no more water being given until the balls are soaked ready for potting. Allamandas do not require such a long rest as many suppose; six or eight weeks are ample, and the plants are ready for starting again.
The system of pruning I adopt is to treat Allamandas like Vines, after the foundation is laid to cover the required space. The plants are cut back to one or two eyes, and when pruned have only two rods, similar in every respect to two Vine-rods pruned on the short-spur system. The spurs can be as near or as far apart as cultivators wish. At one time I trained a shoot up every wire, which was about 6 inches apart; but this shaded the house too much for the other plants growing beneath. The growths are now trained nearly 18 inches apart, and the flowers are much finer than when I trained up more shoots.
Shade is beneficial to these plants for a few hours during very hot weather; the flowers last longer and retain a brighter colour.
Insects never attack my plants; but Allamandas are liable to be attacked by a small yellow thrip, which is easily eradicated by freely using the syringe.
When treated as described - both as to rest, priming, and starting sufficiently late - no plants are more easily bloomed profusely during autumn, winter, and spring. Wm. Bardney.