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.
Possessing many features in common with the Rhododendron, to which they are so closely allied, that, with the single exception of our native species Procumbens, the older botanists classed them in that genus, - the Azaleas are, beyond all question, in the front rank among hardy flowering shrubs. Though less vigorous in their habits of growth, and lacking that imposing grandeur so much admired in the Rhododendrons, they recommend themselves by their remarkably profuse blooming qualities, and by the exquisite richness and variety of the colours of their flowers, embracing, as they do, all the shades of crimson, rose, pink, orange, yellow, and white; and these, in the several sorts blotched and striped in so many different combinations, give an interest and beauty to the American garden in May and early in June, which is at once peculiar and striking, and which must be seen to be adequately realised.
All the really hardy Azaleas are deciduous, and, with the exception of Pontica, which was sent home from the Levant about the end of last century, the few species that have formed the parents of the great majority of the now almost innumerable varieties are natives of North America, and though introduced into Europe at intervals between the years 1734 and 1818, little was done for a long time by way of producing new varieties by hybridisation - the variations being chiefly sports or natural hybrids, the result of the different sorts being grown together. About thirty years ago, however, some of the Continental cultivators took up the matter systematically, and the brilliant varieties known as Ghent Azaleas, a term now popularly applied to all the hybrids, were the fruits of their labours. This work of improvement has been since steadily carried on, both on the Continent and in this country; and in later years the Chinese species Sinensis has been judiciously intermixed with the hardy sorts, the result being seen in the increased size, improved form, and clearer colours of the flowers of the newer varieties.
So far, indeed, have the original American species, such as Calendulacea, viscosa, nudiflora, and speciosa, been eclipsed and superseded by their progeny, that they are now almost out of cultivation in their normal state.
The Oriental species are for the most part too tender for outdoor culture in Britain. Though one or two of those introduced a few years ago from China have been found equal to our winters in the open air - such as "obtusa," and "amcena" - they bloom and start too early into growth to escape damage from spring frosts, precluding them from being so extensively used as outdoor plants, and from receiving that prominence to which, but for that unfortunate drawback, their beauty and profuse blooming qualities so richly entitles them. Amcena is one of the hardiest and most showy of the group, producing its rich rosy crimson blossoms in April, and forming a neat dwarf round bush, densely furnished with small dark-green leaves, rendering it, apart from its flowers, a useful marginal shrub for clumps or beds of plants of taller growth, and well worthy of a place in the American garden, even though it should sometimes require a little attention during its flowering season, in the way of protection at night from frost.
It is worthy of notice that it is a superb conservatory plant, and may be forced into flowering at Christmas with great facility, and if moderately shaded, remains a long time in perfection; for this purpose they must be potted early in November, and placed at once under glass, and introduced into the forcing-house from time to time, as they are wanted in flower.
The arrangement and distribution of Azaleas in the American ground must always depend upon the taste and convenience of the cultivator. Under ordinary circumstances, they require neither artificial watering nor more shelter than is usually afforded to other ericaceous plants. They are found growing naturally in dry situations, and prefer gritty fibry peat; and though, in common with Rhododendrons, they require a good amount of moisture while making their growth, which may be supplied them with the greatest advantage when the weather is exceptionally dry during that season, they will not thrive in a wet swampy position where the soil is continually saturated with water during winter; in such a condition the roots soon decay, and, as a necessary consequence, the plants lose their vigour and gradually die. In preparing ground for their reception, therefore, care should be taken to have it sufficiently drained to prevent the possibility of stagnation; and in the case of retentive clay soils, it is a good plan to raise the beds considerably above the surrounding level.
When a choice can be had, preference should be given to a west or north-west aspect, as they are there protected from the full glare of the sun, and less apt to suffer from continued drought, while the partial shade keeps the flowers longer in perfection. They may be transplanted any time between the autumn, after they shed their leaves, till they begin to show signs of activity in early spring; in this operation the roots should be carefully preserved - the less the ball is mutilated the better, and more likely to secure success.
Azaleas, being so distinct in their general appearance from the rest of American plants, give a pleasing variety, and appear to great advantage, when associated with Rhododendrons and other evergreens in mixed borders or beds; or when, as is very frequently done, grouped in masses by themselves, they have a most magnificent effect - their elegant foliage, richly coloured and in some cases fragrant flowers, produced in such profusion, amply compensating for that naked appearance in winter which is sometimes urged as an objection to this mode of planting.
In the following list are a few of the finest varieties in cultivation - all of them thoroughly hardy, profuse bloomers, and with effective colours: -
Adelaide. Alba flavescens. Ardens. Aurea speciosa. Aurantia major. Aurantiaca cuprea.
Bicolor grandiflora. Calendulacea coccinea.
„ ,, rosea.
Criterion. Cruenta. Cuprea eximea nova.
,, grandiflora. Corusca. Compte de Flandre.
Coccinea major. Cliviana. Coronaria. Delicata nova. „ rosea. Duchess of Parma. Eropereur de Russie. Elector.
Elegans Mortierii. Fulgens. Gloriosa. Genio Mortierii Gloria muudi.
„ triumphans. Incomparabilis. Imperatrix. Ignescens. Leopold I.
Lutescens grandiflora. Lateritia striata. Nudiflora carnea.
,, pallida. Prince Frederick. Pontica.