Thuja-Arborvitae . Evergreen trees of imposing dimensions found wild in North America, China, Korea, and Japan. The several kinds are among the most decorative evergreens and, as they are hardy, they can be used in most parts of North America where suitable soil conditions prevail and the atmosphere is moderately free from impurities. The leaves are very small and almost scalelike, and they closely overlap on the shoots, giving a frondlike arrangement.
In general appearance these trees resemble Chamaecyparis, but the cones are different in shape and the seeds in several instances have larger wings. Although there are not many species or wild kinds, there are a very great num ber of horticultural varieties of some of these species.
When bruised, the branches of some kinds, particularly T. plicata and T. occidentalis, emit a characteristic odor rather like a mixture of Tansy and Turpentine. Thuja belongs to the Pine family, Pinaceae. Although the spelling Thuya was widely used until a few years ago, and still is in many places, research has decided that the correct rendering is Thuja, which is a variation of Thuia, a name used by the Greek scholar Theophrastus.
Propagation by Seed
Seeds should be used for propagation purposes whenever possible. When large numbers of trees are required, the seeds may be sown in late spring in prepared beds of light soil out of doors as are Pine seeds. They should have only a slight covering of soil, for the seeds are very light, and sowing should take place on a calm day.
Small quantities of seed may be sown in pots or flats of light soil placed in a greenhouse or frame early in February. The young plants should be planted in a nursery bed in May or, if that cannot be done, they should be potted singly in small pots and be plunged (buried to the rims of their pots) in a cold frame.
The numerous varieties of the different kinds can be increased by cuttings of young shoots inserted in a bed of sand or sand and peat moss in a warm greenhouse in September or October, or in a similar bed in a cold frame, during August, and left undisturbed until well-rooted. They can also be increased by grafting them, in a warm greenhouse in winter, on stocks of their respective types which have been previously established in pots. As a rule, trees raised from cuttings are found more satis factory than those which have been grafted.
Although these trees are not very satisfactory when planted on very limy soils (high pH), they thrive where a limestone subsoil is covered with a moderately deep layer of non-limy (noncalcareous) soil. Otherwise, they succeed in somewhat acid soils, sandy soils, and those of a peaty nature, where the climatic conditions are rather moist. They should be planted in permanent places when moderately small, though when properly lifted, with the roots balled and burlaped (see Ball), specimens 8-10 ft. high and even higher can be moved without much danger of loss or serious harm. The more vigorous kinds grow rapidly once they are established, and very soon form sufficient growth to screen out un sightly objects when used for that purpose. Planting may be done in mild weather in early fall or spring. ·
As Hedge Plants
Some of the Thujas form good hedge plants and screens. When they are grown as decorative trees very little pruning is necessary other than restricting them to a single leader and removing any lower branches that may deteriorate as the trees age. When grown as hedges they may be sheared once or twice a year but care should be taken not to cut back into wood more than one year old.
There are numerous varieties of Thujas of the dwarf habit of growth which are excellent for rock gardens and foundation plantings. They grow slowly and keep compact. Several of these are referred to under their respective types be low.
Thuja Wood Is Durable
Thuja wood is used for construction, cabinetwork, and cooperage; it is favored for purposes where great durability is required when wood must be exposed to weather changes. So resistant to decay is the timber of this tree, that instances have been known of trees falling in the forest, seedlings appearing on the fallen trunks, rooting into the ground, and growing into specimens showing 300 to 400 annual rings and eventually being cut for timber; the original logs remained sound and were cut up and used for shingles.
T. occidentalis, the American Arborvitae, is a native of eastern North America, where it is a widely distributed tree, often growing on wet ground. In a natural state it grows 60-70 ft. high, with a trunk of moderate size or some times up to 5 ft. in diameter. The frondlike branchlets are compact and clothed with tiny scalelike leaves, each one carrying a globe shaped oil gland on the back. When the leaves are crushed, a strong tansy-like odor is given off. The cones are small and brown; as a rule, fertile seeds are found at the base of two of the scales. There are many varieties. The typical T. occidentalis and some of its varieties turn an un attractive yellowish color in winter.
Golden-leaved Varieties. Notable are aurea, Douglasii aurea, lutea, lutescens, semperaurea, and Vervaeneana, all with yellowish or golden foliage; the last-named turns to a bronze tint in winter. Several varieties are distinguished by their stiff, pyramidal outline-Buchananii, com pacta, conica, fastigata, filicoides (in this the branchlets are divided into fine sprays), River sii, robusta, Rosenthalii and viridis.
Dwarf kinds are Boothii, dumosa, globosa, Hoveyi, nana, pumila (Little Gem), pygmaea, recurva nana and umbraculifera. Varieties with abnormal or curious branch systems are filiformis, Ohlendorfii and pendula. In Ellwan geriana and ericoides the juvenile foliage is maintained throughout life.
T. orientalis, Oriental Arborvitae. At one time this was placed in the separate genus Biota, by reason of its differing from other kinds in its fleshy cone scales and large seeds. Under natural conditions, it may grow 50-60 ft. high with spreading branches. In cultivation, it is usually seen as a compact, shapely tree, with numerous erect branches, up to 20 or more feet high. When planted in exposed places there is a defi nite tendency for the branches of old trees to be separated by wind, and it may be necessary to tie them together for security.
The tree is very variable in character, but the typical form and many varieties can be recognized by the way the secondary branches stand out at right angles, or edge-on, to the main branches. The leaves are small, scalelike, and
Bright green in summer but they may turn to a brown or bronze shade in autumn and retain that shade until spring when they regain their original green coloring. It is not a very fast growing tree and is useful where space is limited. There are many varieties, some of them being notable for their rich golden color.
Useful varieties are aurea, a compact shrub of the globelike outline with golden foliage; semperaurescens, a low, slow-growing bush with golden leaves; bonita, a slow-growing bush of conelike outline; elegantissima, a pyramidal variety with golden leaves in the spring but the color may deteriorate later in the year; Hillieri, a compact, slow-growing bush with yellowish leaves in summer, turning green in autumn; minima glauca, a very dwarf form with blue green leaves, suitable for the rock garden; Rose dalis, a dwarf form with the juvenile type of leaf prominent; flagelliformis, with long, slen der, abnormal branchlets; meldensis, an erect, narrow, compact shrub with bluish-green leaves which are often of the juvenile type; and stricta, a tall plant of narrow, stiff, erect habit.
T. plicata, the Giant Arborvitae, is a very handsome tree, native to western North America, where it sometimes grows 200 ft. high with a trunk of considerable size. It grows rap idly and its rich green foliage is very attractive. When bruised, the leaves emit a characteristic tansy-like odor. In addition to its value as a decorative tree, it is also planted under forest conditions. The timber known as Western Red Cedar is the wood of this tree.
A number of varieties of T. plicata have been given distinctive names. Good ones are atrovi rens, with dark green leaves; aurea or zebrina, with golden and green leaves intermixed; fastigiata, of columnar form; Hillieri, a slow-growing, densely branched form; and pendula, with slen der, abnormal, pendulous branches. T. plicata has also been known as T. gigantea and· T. Lobbii.
T. Standishii, the Japanese Arborvitae, is sometimes called T. japonica. In Japan it grows up to 50 ft. high. It is a handsome tree and well worth planting.
T. koraiensis is the most recently introduced kind. A native of Korea, it first became known about 1918. It may form a low spreading bush, or grow into a small tree, 20-25 ft. high. In a young state, it tends to spread widely at the expense of height. The leaves are dark green above and silvery beneath.