Tsuga is a genus of 10 species of evergreen, monoceious, coniferous trees found in forest from the Himalayas to north Burma, west Vietnam, China, Taiwan and Japan, it is also found in North America.Tsuga species feature flattened, usually linear leaves (similar to that of Yews), with silvery white bands beneath.
Tsugas are typically tall, graceful trees with spreading branches that droop downwards at the tips creating a cascading effect.
The bark is a cinnamon red colour and it becomes deeply furrowed with age. Cones are small and pale brown when mature; after dropping their seed they remain on the tree for a quite a long time.
They are medium-sized to large evergreen trees, ranging from 10–60(–79) m tall, with a conical to irregular crown, with the latter occurring especially in some of the Asian species.
The leading shoots generally droop. The bark is scaly and commonly deeply furrowed, with the colour ranging from grey to brown. The branches stem horizontally from the trunk and are usually arranged in flattened sprays that bend downward towards their tips.
Short spur shoots, which are present in many gymnosperms, are weakly to moderately developed. The young twigs as well as the distal portions of stem are flexible and often pendent. The stems are rough due to pulvini that persist after the leaves fall. The winter buds are ovoid or globose, usually rounded at the apex and not resinous. The leaves are flattened to slightly angular and range from 5–35 mm long and 1–3 mm broad.
They are borne singly and are arranged spirally on the stem; the leaf bases are twisted so the leaves lie flat either side of the stem or more rarely radially. Towards the base the leaves narrow abruptly to a petiole set on a forward-angled, pulvinus.
The petiole is twisted at the base so that it is almost parallel with the stem. The leaf apex is either notched, rounded, or acute. The undersides have two white stomatal bands (in T. mertensiana they are inconspicuous) separated by an elevated midvein. The upper surface of the leaves lack stomata, except in T. mertensiana.
They have one resin canal that is present beneath the single vascular bundle.
Tsuga mertensiana foliage and cones.
The seed cones are borne on year-old twigs and are small ovoid-globose or oblong-cylindric, ranging from 15–40 mm long, except in T. mertensiana, where they are cylindrical and longer, 35–80 mm in length; they are solitary, terminal or rarely lateral, pendulous, and are sessile or on a short peduncle up to 4 mm long. Maturation occurs in 5–8 months, and the seeds are shed shortly thereafter; the cones are shed soon after seed release or up to a year or two later.
The seed scales are thin, leathery and persistent. They vary in shape and lack an apophysis and an umbo. The bracts are included and small. The seeds are small, from 2 to 4 mm long, and winged, with the wing being 8 to 12 mm in length. They also contain small adaxial resin vesicles. Seed germination is epigeal; the seedlings have four to six cotyledons.
Species suitable for bonsai include;
TSUGA CANADENSIS/ Eastern or Canadian Hemlock
A broadly conical tree to 25 metres tall in its native eastern North America. T. canadensis has linear finely-toothed, mid-green leaves to 2cm that taper from their bases and are 2-ranked. There are many varieties of Tsuga canadensis available including dwarf and prostrate forms. Frequently seen is Tsuga canadensis 'Jedoloh' which has a common name of 'Birds Nest Tree because of its habit of spreading and forming a depression in the crown that resembles a birds nest.
TSUGA HETEROPHYLLA/ Western Hemlock
Narrowly conical tree with narrowly-oblong, finely-toothed, glossy dark-green leaves 0.5-2cm long which are 2-ranked. Native to west North America (Alaska to California) where it can reach heights of 20-40metres. (Extremely shade tolerant but requires extra shelter from the wind).
TSUGA DIVERSIFOLIA /Japanese Hemlock
Broadly conical, later domed tree, orange bark and orange shoots with short, fine hairs. Linear leaves are very glossy, dark-green, 0.5-2cm long and 2-ranked. Native to north Japan where it can reach heights of 15metres.
FEEDING Every two weeks throughout the growing season.
REPOTTING Every two years in Spring as new growth starts, use a basic soil mix.
PRUNING Hemlocks grow very slowly and as new growth is similar in colour to mature foliage (except Tsuga heterophylla) growth extension can grow unnoticed and trees can easily get out of shape. Prune hard in late-Winter any trees that have grown out of shape. Wiring can be done at any time of the year though care should be taken not to damage tender new growth in Spring. Cut back fresh growth as it extends to produce a more compact second flush of growth and back budding from the base of old needles.
Take care when wiring as Hemlock have a habit of marking easily.
PROPAGATION Sow seed outside in Spring. Root semi-ripe cuttings in late Summer or early Autumn.
PESTS AND DISEASES Largely trouble free.
STYLING Suitable for all forms except Broom, in all sizes.
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