Conifer Trees: Thuja

THUJA

This genus although being only a small one has produced many fine garden plants. In many ways they are similar to the Chamaecyparis, forming shrubs or trees of mainly conical habit and reproducing freely from seed. The tendency for many clones of similar appearance to get into general cultivation has produced similar problems to the Chamaecyparis. Three species of Thuja; occidentalis, orientalis and plicata have given us useful garden forms. They all have certain characteristics in common, fattened branchlets and scale-like overlapping leaves. One or two species have distinctly aromatic or pungent foliage, the choice of words to describe this is usually dependent upon individual tastes!

The Thujas are adaptable to most soils, but are usually less happy in swampy or badly drained situations. Thuja orientalis is the only species which could not be considered completely hardy in the coldest climates. Although hardy in Great Britain it will not normally survive Scandinavian winters nor below Zone 6 in the United States. Two species, occidentalis and plicata make excellent hedges. The considerable variety of sizes and colours represented make the Thujas an invaluable genus for inclusion in any garden.

This species is the hardiest of the Thujas and is often used for hedging where T. plicata would not be sufficiently hardy, the latter undoubtedly making the better hedge. It has produced a great number of large, slow growing and dwarf cultivars.

Thuja occidentalis

The “White Cedar” or “American Arborvitae” originates from the Eastern United States, from Nova Scotia in the north, to Tennessee in the south. It is somewhat variable in the wild, but usually columnar in habit, reaching a maximum of 20m. Or so. The branches are spreading, the branchlets flattened and spray-like. The leaves have conspicuous resin glands, are dark green on the upper surface, pale green underneath and turning bronze in winter. To my mind it has a pleasant odour when crushed, although

Thuja occidentalis ‘Hetz Midget’

Dwarf Tree. After ten years: 25-30cm.Ultimate Height: 50-60cm. x Ultimate Spread: 60-75cm.

This is an American introduction and promises to be quite a popular little plant for the rock or miniature garden. It is dark green and probably the slowest growing of all Thujas. There is a dwarf globular cultivar introduced recently from Denmark, called T. o. ‘Danica’, which promises to become quite popular.

Thuja occidentalis ‘Holmstrup’

Dwarf Tree. After ten years: 1-1.5m. Ultimate Height: 3-4m.

Thuja occidentalis ‘Holmstrup’Also known as T. 0. ‘Holmstrupensis’ this cultivar deserves to be better known. It makes a neat conical bush with tightly packed rich green foliage maintained well through most of the year. It will in hard winters become slightly bronze tinged.

Thuja occidentalis ‘Lutea Nana’

Dwarf – Medium Tree. 1-1.5m. Ultimate Height: 3-4m. Although much slower growing than the form ‘Lutea’ this does not appear as though it will remain dwarf for long. It is an excellent cultivar, being almost more golden-yellow in winter than in summer. It has been compared to ‘Rheingold’, but differs in being much more erect in habit with no juvenile foliage and much more yellow in colour. It should certainly in time become a very popular plant.

Thuja occidentalis ‘Wareana Lutescens’

Dwarf – Medium Tree. After ten years: 1-2m. Ultimate Height: 4-5m.

This is an excellent cultivar which is likely to become popular when better known, even though it has had every opportunity, being first introduced as long ago as 1884! It is slow growing, eventually making a small to medium sized conical tree. The foliage is compact with flattened sprays, the colour a light white-yellow green in summer, turning an attractive cream inside the plant during the winter. The delicate shades of colour are quite distinctive. It is also listed under the name T. 0. ‘Wareana Lutescens’.

Thuja occidentalis ‘Pyramidalis’

Medium Tree. After ten years: 1.5-2.5m. Ultimate Height: 4-5m.

This cultivar makes a useful formal tree, being mid-green and narrowly pyramidal in outline. There is a form grown widely in the United States, T, o. ‘Nigra’ which is broader based and deep green, the colour being maintained throughout the year. Both these cultivars are excellent for hedges and tolerate all conditions, from full sun to quite heavy shade.

Thuja occidentalis ‘Recurva Nana’

Dwarf Tree. After ten years: 25-30cm.

Ultimate Height: 60-70cm. x Ultimate Spread: 1m.

A useful plant for the rock garden, making a low growing flat-topped dome with erect and spreading branches. The branchlets are curiously recurved or half-turned at the end of the branches. It is light green in summer, bronze in winter.

Thuja occidentalis ‘Rheingold’

Dwarf Tree. After ten years: 1-1-5m. Ultimate Height: 3-4m.

Two forms are given for this popular plant because of its irregularity at different stages of growth. Many forms which have been propagated from juvenile foliage, normally taken from the base of the plant, make compact, rounded bushes, whilst those that have been taken from the upper part make a more open, conical form. The globose juvenile form will in time attain adult foliage and so become more conical in shape and resembling the typical plant shown in the photograph. The photograph shows the different types of foliage quite clearly. Whatever its-shape ‘Rheingold’ is one of the best of all garden conifers, old gold in summer and turning a rich copper-gold in winter. It is very effective in the heather garden, contrasting with the winter flowering heaths. Some authorities claim there is a distinct form in T. o. ‘Ellwangeriana Aurea’, but I have never been able to discern any difference.

Thuja occidentalis ‘Smaragd’

Medium Tree. After ten years: 2-2.5m. Ultimate Height: 4-7m.

This cultivar was raised in Denmark which explains the cumbersome name. It is known in France as T. o. ‘Emeraude’ which is at least more pronounceable to the English tongue! It has a neat pyramidal habit, is a good plant for hedging and has the additional advantage of holding its bright green colour throughout the winter.

Thuja occidentalis Woodwardii’

Dwarf Tree. After ten years: 50-60cm

Ultimate Height: 1.5-2m. x Ultimate Spread: 2-3m.

A strong growing cultivar of rich dark green, this makes a dense globular bush with rather coarse open foliage, arranged in a vertical plane. It maintains its globular shape without trimming and is particularly useful in certain regions because of its extreme hardiness and because it holds its colour well throughout the year.

Thuja orientalis

The “Chinese Arborvitae” was at one time considered a distinct genus and the generic name Biota is still referred to in some books and nursery catalogues. It is normally a large rounded shrub or small conical tree to about 10m. The branches and branchlets are erect, with flattened sprays bearing small green leaves. These leaves are the same colour both sides of the spray and the species can be distinguished further by being less aromatic than the other Thujas and by its recurved cone scales. It has given us some extremely attractive garden forms, although some are of doubtful hardiness.

Thuja orientalis ‘Aurea Nana’

Dwarf Tree. After ten years: 60-70cm. Ultimate Height: 1.5-2.5m.

The form normally grown under this name makes a globose, densely foliaged plant, golden-yellow in summer, yellow or bronze-green in winter. It has erect, flattened foliage sprays arranged vertically giving the plant a very compact, neat appearance. It is widely known in the United States as T. o. ‘Berckmannii’ or “Berckman’s Golden Biota”, but this name was originally given to T. o. ‘Conspicua’ described below. Because there have been a great many golden seedlings of Thuja orientalis raised and introduced into the trade some confusion is inevitable, but the plant shown and described here is generally accepted as the correct ‘Aurea Nana’. It is one of the best of all conifers and would certainly have to be included in the British top ten!

Thuja orientalis ‘Conspicua’

Medium Tree. After ten years: 2m. Ultimate Height: 4-5m.

This cultivar compares more than favourably with the more popular golden Chamaecyparis lawsoniana cultivars. It is of medium growth with golden-yellow foliage maintained better than any other orientalis form. This was raised in the United States by Mr. P. J. Berckmans and should logically bear his name rather than the form ‘Aurea Nana’. It should become more popular in England when better known.

Thuja orientalis ‘Elegantissima’

Medium Tree. After ten years: 1.5-2m. Ultimate Height: 4-5m.

This is another golden form, differing from ‘Conspicua’ in being somewhat slower in growth, with much more compact foliage which turns from old gold in summer to an attractive bronze in winter. All three of the golden cultivars mentioned are worthy of inclusion in any garden.

Thuja orientalis ‘Juniperoides’

Dwarf Tree. After ten years: 45-60cm. Ultimate Height: 1m.

Also known as T. o. ‘Decussata’ this is one of the juvenile forms of the species and like all of these types it makes a rounded bush, never more than lm. In height. It has dense foliage, greyish-green in summer turning to a rich purple in winter. Unfortunately these forms tend to open up with age and are easily damaged by snow. They are the least hardy of the Thujas and a reasonably a sheltered spot should be found for best results.

Thuja orientalis ‘Rosedalis’

Dwarf Tree. After ten years: 40-50cm. Ultimate Height: 75cm.-1m.

Probably the most popular of the juvenile foliage forms, it is distinctive in that it changes colour three times a year. In winter it is purple-brown turning in spring to bright butter-yellow then to light green in summer.

The foliage is very soft and this together with its colour change distinguish it from another juvenile form ‘Meldensis’. ‘Rosedalis’ is sometimes referred to as ‘Rosedalis Com pacta’.

Thuja plicata

Large tree. After ten years: 5-7m. Ultimate Height: 30-60m.

The “Western Red Cedar” is one of the most important timber trees in North America, but it is also of great ornamental value being used widely for screens and hedges. It was introduced to the British Isles by William Lobb in 1853 and is often still incorrectly referred to as T. lobbii.

It is a fast growing pyramidal tree with cinnamon red or brown shredding bark. The leaves are a mid shining green above with whitish markings beneath, borne on large flattened sprays. The foliage has a very pleasant odour when crushed. It is an adaptable species and although happier in moist soils, it will tolerate highly alkaline and dry conditions. It makes an excellent hedging plant, withstanding clipping well and it has the added advantage of branching into new growth from old wood. There have been many good garden cultivars arise from this species.

Thuja plicata ‘Atrovirens’

Large tree. After ten years: 5-7m. Ultimate Height: 30-60m. This selected form of the species differs in its dark glossy green leaves and its more conical habit. It is an excellent plant for hedges, being more consistent in form and colour than the species.

Thuja plicata ‘Rogersii’

Dwarf Tree. After ten years: 25-30cm. Ultimate Height: 1m.

This is in my opinion one of the best dwarf conifers on account of its neat compact habit and excellent colour held the year round. The inside of the bush is dark green whilst the outside tips are golden-bronze. It is normally globular in shape, but throws the occasional strong leading shoot which sometimes gives it a more conical habit.

Thuja plicata ‘Stoneham Gold’

Dwarf Tree. After ten years: 50-75cm. Ultimate Height: 2m.

This is as yet little known, but promises to be one of the best golden dwarf conifers in cultivation. It makes at first an irregular shaped plant, but eventually becomes erect or broadly conical. The inside of the plant is almost black-green and the outside a wonderful orange-yellow tinged bronze at the tips. The two-toned effect is very striking and as the colour is well maintained throughout the winter this cultivar is of great garden value and likely to become very popular.

Thuja plicata ‘Zebrina’

Large tree. After ten years: 3-4m. Ultimate Height: 15-20m.

Slower growing than the species, this makes a very attractive conifer with its light green foliage striped with greeny-yellow. In early summer it is particularly attractive with the whole plant giving a golden appearance and the green less evident. It will eventually become a large tree, so space should be allowed for its development.

01. September 2011 by admin
Categories: Conifers, Trees | Tags: , | Comments Off on Conifer Trees: Thuja

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