This section is from the book "The Gardener V3", 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.
This is a small but very interesting genus of evergreen shrubs and bushy trees, for the most part natives of North America, all of them very ornamental, thoroughly hardy, and of remarkably free growth in almost every kind of soil.
All the species and varieties possess in a greater or less degree that upright, densely branched, conical habit of growth, so characteristic of the Cypresses, but so distinct in appearance and so uniformly handsome, that they are rarely absent even in small collections of choice shrubs.
Of the sorts in cultivation, the following deserve special mention: -
Thuja Occidentalis (the Western Arborvitae) is indigenous to, and occurs in great abundance over, a large area in Canada and the United States, where it is commonly called the " White Cedar," and from whence it was first introduced into Britain about 1596. It is usually found growing in low sheltered swamps, and on the moist banks of rivers, where the soil is of a peaty or rich alluvial character, rising to heights of from 30 to 50 feet.
The timber being close-grained and remarkably durable, as well as light and easily wrought, is extensively used in America for fencing, house-building, and a variety of other purposes.
As an ornamental shrub, for which it is alone cultivated in this country, it has long been highly popular; its symmetry of outline, profusion of graceful plumy branches, along with its beautiful light-green summer's tint, renders its presence ever welcome, either in mixed groups of shrubs, or as single specimens on the lawn; and though it assumes a somewhat sombre russet brown on the approach of winter, it is even at that season, as a contrast to the lively greens of many of the Cypresses and Junipers, strikingly pleasing and effective.
From its dense bushy habit and facility of growth in almost all soils and situations, if moderately moist, this species is well adapted for forming garden-screens or ornamental hedges, which, if the operation is performed in early summer, may be pruned or trimmed into any shape with the greatest impunity.
The following varieties are distinct and handsome, equally hardy with the species, and well worthy of cultivation among select shrubs: Ericoides, a neat dwarf bushy plant, with a great profusion of tiny heath-like branches - called by the American nurserymen, with whom it originated, Tom Thumb - is useful for planting in front of groups of the larger shrubs, in flower-garden beds, or on lawns of limited extent. Compacta differs from the species in having a dwarfer habit, the branches more compressed, and produced in greater abundance; it is one of the prettiest of cone-shaped lawn specimen-plants. Pendula is a curious weeping form, somewhat sparingly branched, and is an interesting variety in a collection. Variegata has some of the branchlets tinted with a bright golden variegation, and though more slender than the species, is a desirable lawn-plant.
Thuja Plicata (The Plaited-Leaved Arborvitae) is found wild on the western shores of North America, particularly at Nootka Sound, growing in deep alluvial soils to heights of from 20 to 30 feet. This fine species was introduced into Britain about 1769, and has proved itself to be a thoroughly hardy and free-growing ornamental shrub, of a compact, conical habit of growth, abundantly furnished with short, stout, horizontal branches, much divided into thick branchlets disposed in regular rows, and these, overlapping each other, give the plant that peculiar appearance which doubtless suggested the specific name Plicata, or Plaited. In summer the branchlets are of a light, slightly glaucous green, changing in winter to a rich brownish tint.
Though one of the commonest of our hardy Coniferous shrubs, it is well worthy of a place of honour among the rarest and most select, and handsome enough for a lawn, or any other site where a distinct symmetrical evergreen of moderate size is desirable.
It thrives best in a deep, cool, moderately moist soil, and should always be allowed plenty of space to develop its branches on every side.
The Variety Minima is a neat-growing, bushy plant, very useful for planting on and around rockeries in small garden beds, or in terrace vases; and as it is quite as hardy as the parent, thrives in very exposed situations. Another well-known form called Wareana, formerly classed as a distinct species, but now by most authorities regarded as only a variety of Plicata, has a slightly more robust habit of growth - a distinction, however, that is not always very obvious, and which seems to depend very much upon the soil, or other circumstances under which the plants are grown.
This species, hitherto known and distributed under the names Menziesii and Lobbii, is now ascertained to be the true Gigantea first described by Nuttal in his ' Plants of the Rocky Mountains,' the plant erroneously so named being the Libocedrus decurrens, a tree that, even under the most favourable circumstances, in its native woods rarely rises higher than 50 feet, whereas Gigantea grows to heights of from 100 to 150 feet.
This grand tree is found wild at altitudes of from 4000 to 5000 feet, over immense tracts on the north-west coast of America, and in California, from whence seeds were first sent home by Jeffrey in 1854.
Though as yet only seen in this country as a large shrub, or at most but beginning to assume the tree form, and chiefly confined to parks and pleasure-grounds, it has been widely distributed and extensively planted, so that its thorough hardiness, freeness and rapidity of growth in almost every district and variety of soil, have been amply demonstrated, and there is every reason to believe that it will yet come to be regarded as one of the most valuable of British forest-trees.
In a young state, and as seen in our pinetums and parks, it is one of the most beautiful of its tribe, having a handsome conical habit of growth, clothed to the ground with long graceful branches, much divided into feathery branchlets, of a shining, warm green colour, which is maintained all over the year.
Among varieties, of which many may be detected in almost every lot of seedlings, Craigiana is the most distinct and constant. This fine form was raised from the original seeds sent here by Jeffrey, and differs from the species chiefly in having a more open habit of growth, with the branches slightly pendant, and turned up at the extremities. It is quite as hardy and of as free growth as the parent, and makes a very pretty specimen-plant. Hugh Fraser.