This section is from the book "The Gardener V2", 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.
Of this genus of American shrubs it is unnecessary to say more, by way of commendation, than that it contains among the few species of which it is composed some of the most handsome Evergreens in cultivation, and that they have long been extensively grown and universal favourites both in general shrubberies and in collections of peat-soil plants.
Introduced at intervals between 1734 and 1825 from North America, where they are diffused over a very wide area, growing in rocky woods and high mountain-bogs, some of the species pervading large tracts in a similar manner with the Calluna vulgaris of our moorlands, they have proved themselves perfectly hardy and easily cultivated in this country, growing with the greatest luxuriance under the ordinary conditions necessary for the other American plants.
All the species have bright showy flowers, elegant foliage, and neat habits of growth, forming close dwarf bushes, in some cases only a few inches, and never above 4 or 5 feet, in height. The blooming season extends over a considerable period of the spring and summer, some of the sorts coming out early in April, in favourable seasons in March, while others are not in perfection till July.
Along with their attractive colours the flowers are interesting from their singular shape, the corolla consisting of a single tubular-based and spreading-topped petal, the ten stamens bending back from the centre so as to resemble the ribs of an umbrella, concealing the anthers in an equal number of cavities regularly disposed round the inside; these cavities form horn-like protuberances on the outside, and give to the flower the appearance of an elaborately-carved and elegant salver.
While all the species are really evergreen, some of them have a tendency, in very severe winters or in exposed situations, to partially shed their leaves in midwinter or early in spring, before the growth begins; this, however, has no bad effect on the health of the plants, as on the approach of genial weather they begin to grow with their usual vigour, and expand their blossoms at the proper season.
Though light sandy peat is the best soil for all the sorts, they will thrive in a rich arenaceous loam, provided it contains plenty of fibre.
The Kalmias are admirable subjects for pot-culture, as they can be easily forced into early flowering, and are most effective and pleasing additions to the decoration of the conservatory at any season. For this purpose they may be potted, and placed at once in the forcing-house. If wanted very early, however, the best plan is to lift them in autumn, or as soon as it is possible to determine which of the plants are best set with flower-buds, and to protect them from frost till it is time to introduce them into heat.
We note a few of the more distinct and showy species and varieties: -
This pretty species is a native of Carolina and Pennsylvania, where it grows in bogs, swamps, and sometimes in high mountain-lands. It rarely exceeds 3 feet in height, forming a thick bush with Myrtle-like leaves of a peculiar light shining green colour, in themselves very ornamental, and contrasting well with the darker green of most other shrubs. The flowers, which are in perfection about the end of June or beginning of July, are of a delicate pink colour, and are produced from the sides of the branches in bunches. It is thoroughly hardy, and will thrive in any situation with the other peat-soil shrubs. There are several well-defined varieties of this species in cultivation, more or less interesting to horticulturists. Of these we can recommend rubra, with darker-coloured flowers, and pumial, a miniature form, with other characters very similar to the species. Both varieties are well worthy of cultivation.
Kalmia Glauca, from Canada and some parts of the United States, is a well-known and beautiful species, growing from 1 to 2 feet high, dense in its habit, with foliage much smaller than that of the preceding, of a dark-green colour, and glaucous beneath. The flowers are pale red, and are produced in terminal corymbs. It is a most profuse bloomer, and is generally in perfection in the beginning of April, though in mild springs it is sometimes seen in full bloom in the middle of March. It is the best of the family for very early forcing, and may be had in full flower, with a moderate amount of heat, early in January.
A moist situation should always be chosen for this species; and where it cannot be had naturally, it will be found advantageous to supply it liberally with water once or twice during the dry season.
The varieties usually grown are stricta, a well-marked upright form, and superba, with somewhat larger and higher-coloured flowers, but otherwise very similar to the species; both of these are fine, and ought to find a place in the peat-beds.
Kalmia Latifolia, from Canada and a large portion of the United States, popularly known as the Calico Bush or Mountain Laurel, is a magnificent shrub, either in or out of flower, and by far the most showy of the genus. Its leaves are of an ovate lanceolate form, thick in texture, and of a fine shining green colour; the flowers, which are of a fine red colour, changing to a paler tint, are much larger than those of any of the other species, and are produced in large bunches at the ends of the branches; they usually expand from about the middle or end of May till the beginning of July, according to the season. It attains a height of from 8 to 10 feet in this country, and when well grown has a most symmetrical appearance.
The situation best adapted for its growth is one fully exposed to the sun, and so well drained that there is no possibility of water stagnating at the roots: a dry sloping bank or raised bed suits it admirably. It is most impatient of wetness or excessive moisture; under such circumstances it soon gets stunted-like, and rarely forms flower-buds. The best variety of this species in cultivation is Myrtifolia, a miniature form, yet as indispensable as its parent to any collection.