This section is from the book "The Florists' Manual", by William Scott. Also available from Amazon: The Florist's Manual.
Of all the species of this beautiful genus, the Indian or Chinese are the most valuable. The growers of continental Europe have made such a specialty of growing azaleas that it is not likely that we shall for some time look to any other source for our supply. They may have neither soil, climate nor labor more suitable than we have in many parts of this continent, but certain it is that with our present facilities or methods we cannot begin to raise an azalea at anything like the same cost and quality as those imported. New varieties are, of course, raised from seed, and at the third season you will be able to see whether you have any improvements on existing varieties.
They can also be propagated from cuttings by inserting the cutting in sand in March. A cutting of two and one-half or three inches of what is known as half-ripened wood is best; that is, the young growth of spring, not in too green or succulent a state, as you would a verbena, nor too much ripened and hard. A closely shaded frame with some heat under the sand, either from pipes or manure, would be the most favorable condition. They are slow to root, and in our climate the little plants or cuttings are so liable to the attacks of thrips and red spider during the summer months, and so difficult to remove, that propagation by cuttings is not worthy of consideration, either to produce a fine plant or for profitable operation. All the plants we handle in our business are grafted. Desirable and popular varieties are grafted on stocks raised from the seed of some strong growing varieties. Our chief interest in the azalea is how to handle them when they arrive here, and how to care for those unsold, which should make, by good care, fine plants for the second or third year.
It is generally acknowledged that a soil containing lime is very unsuitable for azaleas or any of the order erica-ceae, which includes the heaths, rhododendrons, etc. It will be noticed that in some soils the plants imported and potted in October have made scarcely any young roots into the soil we give them. The Belgians grow them in what may have originally been a peaty soil but it is saturated with manure, and as their azaleas are always planted out it is further enriched by constant doses of liquid manure. They plant them out after danger of frost, lift them if unsold, and plant them on benches during winter, and out again the next summer; with all this disturbance of roots the greatest vigor of health is maintained. But peat is not entirely essential. Two-thirds of turfy loam, not sifted, but just broken up, and one-third of leaf-mold, will make a good compost in which azaleas will thrive. If to the above is added one-tenth of finely sifted decomposed cow manure, so much the better.
When unpacked, the roots are often found dry. They have also rooted so freely that to pot them just as received would require an unwieldy pot. The ball of earth can be reduced one-third by shaking off the soil and this appears to do the plant little or no harm. Considerable of the ball can be reduced by slicing off an inch or so with a sharp knife or hatchet. "When the ball is reduced to the required size - and it should only be done when the roots would require a pot out of proportion to the plant - soak the ball of roots in a tub of water for a few seconds. Pot firmly. If the soil is left loose, it will only be a channel for the water to run down and escape the roots that need it.
For the first two or three weeks after potting, the plants are best in a cool, shady and rather close house or frame; after that, a cool, light house for those you wish to flower the following Easter. By cool I mean 40 degrees at night is ample, and to retard them still more, anything above the freezing point will do. Some varieties cannot be kept for spring, and it is well to bring early varieties along, so that at all times during winter you have some plants in flower. At no time should the roots of the azalea be allowed to get extremely dry. They will not bear it; and it may be well to state right here that the many complaints of our customers that their azalea has shriveled up or the flowers are wilted is nothing but the insufficiency of water. Especially is this the case with the plants when sold the winter following their importation. When in a temperature of over 50 degrees or when any forcing is attempted, the plants should be well syringed at least once, or better, twice a day.
Indian Azalea Dr. Metzger, Grown in Pyramidal Form.
Mealy bug often attacks azaleas. Plenty of syringing will keep them down. Thrips and red spider are also very bothersome to them, but neither of these would appear if syringing were faithfully observed. They can be removed by a syringing of the tobacco extract. The nicoteen extracts diluted fifty to one will do. It is a general belief that tobacco smoke injures the foliage. It may be so, and it is well to avoid it, but I have seen little evidence that it injured the azalea.
During January, February and March the plants imported the previous autumn have a great inclination to make a growth before they develop their flowers. If this growth is not rubbed off the flower will be so weakened by the strong young growth that it will amount to nothing.
Many growers would rather import every year, and if they had plants left over in the spring, throw them away. To the man who grows but a few dozen this is likely to be the most prontable way of doing business; but where there are enough to warrant systematic care, it should not be done, for the second, third or even tenth year they are more satisfactory plants to the purchasers than those just imported. With good but not necessarily costly care the azalea attains a good size and flourishes for many years.
Plants of the previous autumn's importation that are unsold the next spring, and are frequently in bad shape from neglect in stores, should be cut back quite severely, even to the previous summer's growth. Place them in a light, warm house, and syringe frequently. When cutting back, see that the soil is in good shape and the drainage in order. By the first of June they will have made a good growth; that growth is what gives you the bloom the following winter. From the first to the middle of June plunge them out of doors in the broad sun. The pots should be plunged in some material to the rim, but in a place where water will not remain during heavy rains to unduly soak the roots. Over the surface of the pots spread an inch of rotted refuse hops or rotted stable manure. In this position they will do till the end of September, or till there is danger of frost. They want faithful attendance in watering, never to be killing dry, and in hot weather a daily syringing.
We notice when Easter is very late, as the spring of 1905, that many florists lose the sale of their azaleas because they are too early. This is bad management. We know the date of Easter and if very late the azaleas should be kept very cool and if possible away from direct sunlight. It is much easier to do your retarding in the dark winter months than in March and April.
If it is desired to grow on some plants a number of years to make fine specimens, the above treatment in most respects will do, but there are a few exceptions. Plants established in pots will seldom need those early growths rubbed off, for they have not the inclination to make them; neither will they want the hard cutting back every spring, the growth they make after flowering being sufficient for the next year, and stopping strong growths to keep the plant in good shape is all that is needed.
Azaleas by training and tying easily conform to almost any shape. They are beautiful if left to grow quite naturally. They are easily kept by pinching and stopping in what may be called umbrella form, but are grand when trained in pyramidal form. Few cultivated plants can equal a well flowered azalea four or five feet in diameter at base, tapering to two feet at top and six or seven feet high.
Contrary to what would be expected, the plants you have grown during summer are not the ones for Christmas blooming. The newly imported plants must be used for that purpose. Deutsche Perle, white; Simon Mardner, deep rose pink, and Vervaeneana, rose and white, are fine varieties for this early blooming.
It would be useless to mention all desirable varieties. There are hundreds and the Belgians grow in largest quantities the most attractive and free flowering kinds.
Hardy deciduous azaleas. These are the so-called Ghent azaleas and hybrids of A. Mollis. The flowers appear in great abundance before the leaves are developed. They are now imported in large quantities for Easter sales and are very handsome plants. If forced early enough for Easter the flowers are fairly durable, but in the warm days of May they drop quickly. The shades of color are all beautiful and range from pure white to red. Many of the pink and orange varieties are grand in color and when decorated with suitable ribbon are most attractive in our stores and sell well.
The plants arrive with the Indian azaleas and should receive a soaking at the roots and then be potted or plunged and stored away in a coldframe till they are wanted to force. The time needed to bring them into flower will depend upon how early the season is, and more still on the temperature of your house. In a house with a night temperature of 55 degrees allow about six weeks. Any soil will do for them, as it will not pay to carry them over the season unsold. It will be much cheaper to import fresh stock. Our nurserymen recommend them strongly for planting out, and where the rhododendron does well the hardy azalea will also thrive, but in many places they are an entire disappointment and you should be careful about commending them to your patrons.