Betula

Distinctive coloured barks are the outstanding merits of these attractive trees and shrubs.

Betula B.utilis var. jacquemontii
Betula B.utilis var. jacquemontii

The birches (Betula - Betulaceae family) are attractive and visually striking trees to incorporate in a scaled-down garden arboretum/woodland garden or planted as a small group of trees to add structure and form to grass landscape areas. This is especially the case with the white-bark species of Betula.

This was evident on my last trip to New York in 2011. Groves of birch trees add outstanding structure to enhance the sculpture garden at the Museum of Modern Art, an oasis in the heart of the city.

Betula comprise about 35 species of deciduous trees and shrubs located in the northern temperate regions. The outstanding merits of the trees are the coloured barks, comprising whites, creamy pinkish tints, greyish whites and, at the other end of the colour spectrum, reddish browns.

Flakey bark combined with the yellow autumn tints of the leaves provide a spectacular finale in the autumn. This is followed in the winter by a beautiful haunting aura from the white-bark species, especially when the trees are devoid of their foliage.

Male and female catkins are borne on each individual tree. The male catkins extend in length during the spring, while the female catkins have a shorter, more rigid formation.

Betula tolerate a wide range of soils, withstanding dry to damp conditions. Acid soils are the preference for this genus. Their shallow roots can be sensitive to heat. The ideal site is for the roots to be shaded and for the canopy to receive sun for most of the day for the foliage to flourish. Mulching around the roots helps to maintain an even soil temperature.

Birches are rapid growers. As an example, a 30cm seedling can obtain a height of 6m in 10 years. Multi-stemmed birch trees can be formed by planting several smaller trees in a well prepared, suitably sized hole. Interesting shapes can be achieved at maturity. However, from my own personal viewpoint and experience, I would rather not plant trees using this method.

Autumn/winter pruning involves shaping the feathered branch ends to produce a clear central leader. This is worth the effort on grassed landscapes, creating a well-managed effect. It also improves light and air into the trees to reduce diseases. The main pests of birch are borers and leaf miners.

The outstanding white-bark birches originate from North America, Europe and the Orient. All species of birch are able to shed bark in horizontal strips as well as vertically. This action exposes a rejuvenated appearance of layers of fresh colours - cream, pink, brown or even a shining matt.

B. papyrifera, the paper birch, provides spectacular autumn foliage and gleaming winter white trunks. This species provides a sharp outline with the famous white trunks, which takes the effect high up into the leaf canopy. The brilliant white bark of B. jacquemontii from the western Himalayas takes some beating. The bark is a rich creamy colour and it features distinctive dark lenticels.

By comparison in bark colour, texture and form, there is the pinkish, orange peeling bark of B. nigra from central and eastern USA. It is also known as the "river birch" because it grows well in damp ground. The yellow birch B. lutea and B. lenta from north America display brown bark with a polished effect along with yellow, rich-coloured foliage to light up the autumn canopies. Growth rates of this species can exceed 15m.

For bark colour combinations, B. utilis var. jacquemontii 'Grayswood Ghost' Award of Garden Merit (AGM) with striking white bark and glossy leaves planted with brown polished bark species creates an interesting visual dimension.

The main areas of propagation are from cuttings taken in mid spring to early summer and seeds in midsummer to late winter. Most birches are grafted as the main area of propagation. Grafts are taken onto B. pendula - incompatibility may be a problem.

What the specialists say

- Paul Bartlett, manager, National Plant Collection, Stone Lane Gardens, Devon

B. utilis 'Mount Luoji'

"A very dark birch. The origins of this species are in Sichuan province, China. The bark is a deep chocolate brown. This is complemented with white blooms above the deep-coloured bark. The light coloured lenticels add an interesting contrast on the chocolate-coloured bark. The finale of this outstanding bark feature is the visual peeling effect of the bark."

B. utilis 'Forest Blush'

"From the Yunnan province, China. This is a very distinctive birch. Smooth, pale-coloured bark, beneath which are shades of orange to red. This is covered with a misty white bloom. The result of this colour formation is a soft pink. This is complemented with eye-catching orange lenticels. The leaves are waxy, dark green and comprise a deeper vein than other forms of B. utilis, also with the addition of a curved leaf margin."

B. utilis var. jacquemontii 'Snow Leopard'

"A Himalayan birch, pure-white form. This is a cultivar that was recently introduced from Jammu and Kashmir state, northern India. Among all species of birch this specimen has the whitest and smoothest bark. This form can add interesting structure to the garden with the emphasis being planted in a group. The barks stand out against a shady background as a focal point."

- Dan Crowley, dendrologist, Westonbirt, The National Arboretum

"At Westonbirt we grow a wealth of Betula species, ranging from the brilliant white-barked forms of B. ermanii to dark-barked forms of B. utilis, with a great deal of variety in between.

"In the spring, the long catkins and fresh foliage of the dark B. insignis catch the eye, while in summer the distinctive foliage of the rarely seen B. corylifolia is a welcome sight.

"Among the autumn highlights are the North American B. lenta and B. alleghaniensis, which both colour a brilliant yellow. The latter is also particularly notable for its metallic bark that glistens in the autumn sun.

"Another tree at Westonbirt that is always worthy of mentioning is the UK champion B. ermanii x pubescens. Previously considered to be a true B. ermanii, further investigation has proven it to be of hybrid origin. Regardless of its parentage, it is one of our most fantastic trees and as big a birch as you are likely to see."

- Paul Rawlings, Dulford Nurseries, Cullompton, Devon

"We sell more than 30 varieties of Betula - plenty of the native B. pendula and some of its cultivars, especially B. pendula 'Tristis'.

"The most popular ornamental birch are B. utilis var. jacquemontii. People often ask for the cultivars such as 'Grayswood Ghost', 'Silver Shadow' and 'Trinity College', but the straight jacquemontii has a good white bark and we sell a lot of these. The majority of our birch are produced by grafting."

Species and varieties

- B. alleghaniensis is a medium-sized tree with smooth, shining amber/golden-brown bark that peels away. The leaves are ovate to oblong in shape and the autumn leaf colour is a rich yellow.

- B. lenta is known as the cherry birch. The trunk forms a colour of dark reddish brown or purple. When scraped, the new bark is scented of the oil of wintergreen. The leaves turn a rich yellow in the autumn.

- B. medwediewii is a form that borders a large multi-stemmed shrub/small tree. The branch formation comprises erect spreading branches. Large terminal buds are complemented by large corrugated leaves that turn an eye-catching shade of yellow in the autumn.

- B. nana is the dwarf birch. Its branches have a slender formation. The small leaf structure comprises neatly rounded, toothed leaves.

- B. nigra, the river birch, is a tree that has outstanding beauty. Fast-growing and easily recognised for its orange shaggy bark. On older trees the bark turns a much deeper colour. Renowned for growing to its potential in damp areas. The leaves are diamond shaped, soft green and glaucous beneath.

- B. occidentalis is classified as a large shrub or small to medium-sized tree. The bark is bronze to reddish brown in colour. Leaf structure is sharply double toothed - these are on shoots that are covered in glandular warts.

- B. papyrifera is a large tree with striking white papery bark and yellow autumn foliage. Forms of this species occur in wild areas, producing a bark that is brown in colour.

- B. utilis 'Forest Blush' AGM (H6) comprises smooth white bark with a touch of bluish to pink. The leaf form has been described as elegant. The plant hunter George Forrest collected seeds in Yunnan, China.

- B. utilis var. jacquemontii 'Doorenbos' AGM (H6), the snow queen, is a medium-sized tree that comprises a white peeling bark - when exposed, the colour is a pale orange. This form was selected from a seedling by Dutch dendrologist Albert Doorenbos in 1933.

- B. utilis var. jacquemontii 'Grayswood Ghost' AGM (H6) is a particularly striking form of var. jacquemontii. The bark is an outstanding bright white. Propagated from the parent tree, B. ermanii 'Grayswood Hill' AGM (H6), Surrey.

- B. utilis var. jacquemontii 'Silver Shadow' AGM (H6) is described as one of the loveliest birches, with dazzling white stems. Small to medium sized with outstanding white bark complemented by drooping dark-green leaves.


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