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.
The varieties of this genus in cultivation at the present time are somewhat numerous, and all gardeners are acquainted with a greater or less number of them. The brilliancy and peculiar freshness exhibited by their flowers, combined with the profuse manner in which they are produced on healthy plants, are qualities that place Azaleas in the front rank of flowering plants, and no other class of greenhouse plants can successfully compete with them in the matter of producing a brilliant and striking floral display from January to June. Then the great diversity and purity of colour exhibited in the flowers of different varieties, are points in which Azaleas excel. The flowers of some varieties are pure white, those of others, various shades of pink or rose colour; some have crimson, and others orange-scarlet coloured flowers; and again, there are varieties that have striped flowers of various shades, - so that in the matter of colour they supply a wide field to choose from. Then there is a difference in the shape or formation of the flowers produced by different varieties. Some have double or semi-double flowers, others have single flowers.
Some varieties have the petals of the flowers crisped or frilled, and others have plain or smooth-petalled flowers; then there are kinds that have the petals reflexed, and others that have flowers more or less cup-shaped. Thus, in the colour and formation of the flowers, they present an amount of varied and interesting beauty that is equalled by few other classes of greenhouse plants, and not surpassed by any. Other recommendatory qualities possessed by Azaleas are that, as a rule, they are of a compact habit of growth, and, when properly treated, never fail to produce an annual crop of flowers in great abundance from the time they are 6 inches high by 6 inches through, until they reach as many feet high by the same through. Their free-flowering habit while the plants are small renders them very appropriate' and useful subjects for taking part in floral decorations in the dwelling-house, where such are in request. As subjects for cutting from, they are extremely useful, their flowers being adapted both for bouquet - making and arranging in vases. They are also amongst the hardiest of greenhouse plants, and if the wood is well ripened they will bear without injury several degrees of frost. It is better, however, not to expose them to frost if it is possible to avoid doing so.
And further, Azaleas are easily forced for a supply of flowers in the winter; but the process, to be successful, must be gradual. If the plants are brought at once from the temperature of the greenhouse to a structure where the temperature is say 70° or 75°, the likelihood is that the wood-buds will burst into growth, and the flower-buds will damp off or go "blind," and thereby defeat the end in view. The proper way is to place the plants in a temperature of from 50° to 55° at first, and keep them in this temperature until the flower-buds are seen to be on the move, then a rise of 5° or 10° in the temperature will cause the flowers to expand before the wood-buds have made any great progress in growth.
The last thing I will mention in favour of Azaleas is that they are very "telling" plants at public exhibitions. A healthy well-bloomed specimen is a "strong point" in favour of the collection in which it is placed; and no collection of flowering plants at a spring show can be said to be complete that does not include a good example of some variety of the Azalea. Every one who has seen a Spring Show of the Royal Caledonian Horticultural Society must have noticed the magnificent specimen Azaleas exhibited by Mr John Paterson of Millbank, and others. These plants illustrate, in a striking manner, the profuse flowering qualities of different varieties when under the care of skilful cultivators. The only fault that, in my opinion, could be found with the examples in question is, that there is scarcely "a bit of green" to be seen about them; they are masses of flowers from top to bottom. This is due, in some measure, to the close way in which the shoots are trained; and I am of opinion that even in the case of plants intended for exhibition, it is a mistake to train the shoots in so stiff and formal a manner; and for home decoration Azaleas should have only as much training as will prevent them from having a straggling look.
Still, it would be interesting to some, and useful to many readers of the 'Gardener,' if Mr Paterson would state in its pages the mode of culture by which he suceeds in laying on the colour so thick.
To produce fairly good examples of the Azalea, however, is not a difficult matter, and we will now say a few words on cultural points.
This is accomplished by seeds, cuttings, or grafting, - the former method with the view of producing improved varieties, the two latter with the view of perpetuating and increasing the varieties already in existence. Under favourable conditions cuttings of most varieties emit roots freely. Many varieties, however, do not grow so fast on their own roots as they do when grafted on stronger-growing kinds, and, as a consequence, grafted plants are to be preferred. Only the strongest-growing varieties should therefore be propagated by cuttings, and these principally with a view of supplying stocks on which to graft less free-growing kinds. September is a good time to put in the cuttings. When selecting them, choose mature shoots, of from 2 to 3 inches long, of the current season's growth. Sever them from the parent plant with a sharp knife, and trim off a few of the lower leaves from each. This done, insert them in well-drained pots or shallow pans, filled with peat and silver-sand in equal proportions, well mixed together and firmly pressed in the pots.
After the cuttings are inserted give them a good watering by means of a fine-rose watering-pot, for the purpose of settling the compost firmly about them; then place the pots containing them on the bed or on a shelf in the propa-gating-pit, and cover them with bell-glasses : shade them from direct sunshine, and supply them with water as required until the following spring, when they will be rooted and ready for potting off into separate pots, using a compost similar to that in which they were rooted.
After the little plants are potted off place them in a temperature of about 65°. Shade them from sunshine, and maintain a close humid atmosphere about them for two or three months. Under this treatment they will grow apace, the object being to get them on as fast as possible the first year. Those plants intended to be used as stock for grafting other varieties on should not be permitted to make more than one shoot each, and if all goes right they will be strong enough to receive the grafts in eighteen months from the time they were put in as cuttings. When about to be grafted, the stocks should be placed in a temperature of about 70°, a week or two previous to the operation of grafting taking place. This will cause the sap to be moving in them at the time the scions of the desired varieties are attached to them, and thereby the union between stock and scion will more readily take place. The scions should not be more than 2 inches long, taken from the points of the shoots; and the method of grafting should be what is known as splice or whip grafting. Side-grafting is also a successful method; and both these are so well known to gardeners that I need not describe them.
After the operation is complete, the plants should be placed in a close case in the propagating - pit, and kept shaded and moist until the union is complete, and afterwards treated as established plants. I would remark, however, that at the present time the propagation of Azaleas, in any way, is not much practised by private gardeners. Young plants in a flowering state can be purchased at the nurseries much cheaper than what the same sized plants could be produced for at a private place; besides, it is not at every place where the necessary accommodation is at hand for propagating Azaleas, either by cuttings or grafting.
This may be done at any season, but just as the plants have done flowering is perhaps the best time to do so. Before transferring the plants from smaller to larger pots, the balls of soil about their roots should be thoroughly moist. It is also important to success that the drainage be ample, and neatly arranged in the pots, so that it may act satisfactorily at first, and continue to do so until the plants need repotting again.
A suitable compost for Azaleas consists of sandy loam or good fibry peat - but not a mixture of both - and coarse river-sand, in the proportion of four parts in bulk of loam or peat to one part of sand. "When applying the compost to the roots of the plants make it as firm as possible, and do not fill the pots over full; leave plenty of room for holding water. After being repotted the plants should be placed in a temperature of 60°, shaded from sunshine, supplied with plenty of atmospheric moisture, and a moderate amount of air for six weeks or so - after which time they should get as much air as possible.
About the middle of July the plants should be placed out of doors, where they may remain till the middle of September. While standing out of doors the pots should be placed within other pots, or wrapped round with hay or straw bands, which serve the same purpose - that of protecting the roots from injury through the action of the sun or dry air on the outside of the pots.
No rule can be laid down as to how often this should be done. The compost about their roots should not, however, be allowed to become anything like dust-dry at any season; and on the other hand, a sloppy condition of the compost must be avoided.
Azaleas are liable to be attacked by mealy-bug, scale, greenfly, red-spider, and thrips. The two last insects give most trouble. Thrips in particular have a special liking for Azaleas, and if permitted to overrun the plants, will soon destroy them.
Placing the plants on their sides on a proper platform, and giving them a good washing with cold water by means of the water-engine now and again, will keep red-spider in check, and, at the same time, prevent thrips from making much headway.
If thrips get numerous, treat them to a strong dose of tobacco-fumes on two or three successive evenings. J. Hammond.