Name: birch, silver birch, white birch, river birch, paper birch, Himalayan birch, Betula pendula, Betula sp and cultivars.
Height: usually 6–30m. Dwarf birch, B. nana, is a shrub 0.6–1.2m high.
Plant type: deciduous tree.
Foliage: green leaves with serrated margins in spring, and golden yellow tones in autumn, depending upon the species or cultivar.
Climate: birches require a cool temperate climate and are resistant to frost.
Soil: deep, cool, well-drained fertile soils, but some species can grow in shallow or poor waterlogged soils.
Position: most birches grow best in full sun or partial shade with protection from hot drying winds.
Flowering: separate male and female catkins (cylinder-shaped flowers) are produced from winter to spring. The fertilised female catkins produce copious quantities of winged papery seeds.
Feeding: use an organic controlled release fertiliser specifically for trees and shrubs in spring and again in late summer/early autumn.
Watering: watering 2 to 3 times per week is required throughout the hotter summer months or dry periods as birches have shallow fibrous root systems.
Birches are handsome deciduous trees usually prized for their white to pinkish brown coloured trunks, often with peeling bark. Graceful branches provide perfect dappled shade, bursting with delicate fresh green leaves in spring, which turn to golden yellow in autumn before falling. There are varieties with coloured or weeping foliage, dwarf shrubs and small trees for gardens with limited space, but most are medium-sized trees growing between 6 and 30 metres high. Birches are often planted in groups, just as they are found in nature.
Most birches originate from the cooler parts of the Northern Hemisphere in the temperate zones with some species surviving further north than any other tree species in the cold Artic zone. These zones include Europe, Asia, Siberia and North America. Birches are slender trees with attractive bark and colourful autumn foliage. In Australia and New Zealand, birches grow best in the cooler temperate areas and in higher elevated areas with cold winters. They should be positioned in either full sun or partial shade with protection from hot drying winds, otherwise leaf scorch may occur.
There are now some varieties that are more heat tolerant and better suited to warmer summer conditions, including the cultivar Betula nigra ‘BNMTF’–Dura Heat™. Edna Walling, one of Australia’s most influential landscape designers, famously advised planting birch in haphazard copses or groups of trees, by taking a bucket of potatoes throwing them over your shoulder and planting them where they landed, just as nature intended.
Birches have shallow root systems so they prefer a cool, rich, acidic soil that is moisture retentive, but also well drained. They grow best in a soil pH between 5 and 6.5, so it pays to test your soil first with a pH kit. Incorporate some sphagnum moss and compost at planting. Granulated or liquid sulphur may also be applied to acidify the soil if required. Mulch is advantageous to keep the shallow roots cool during the summer months, particularly in warmer areas.
Birches naturally grow alongside rivers and streams so many varieties can withstand moist or wet soils for extended periods during the warmer months. Some species can adapt to shallow or poor soils but may grow slowly.
Use a controlled release organic fertiliser specifically for trees and shrubs in early spring and again in late summer.
Birches can be affected by a number of pests including aphids, leaf miners, beetles and borers as well as birch leaf spot disease. On young or small trees, treat pests at the first signs with insecticidal soap sprays, horticultural oil or Neem oil. Larger trees will need to be treated by injecting or drenching the soil with an insecticide. This must be undertaken by a qualified tree surgeon or arborist.
Borer treatment is difficult, and infected branches may need to be removed. Metal coat hangers can be used to squash larvae deep in their holes. Birch leaf spot may be controlled on small trees using a copper-based fungicide, and on larger trees by injection from a qualified arborist.
Birch species are usually propagated from seed collected in summer. This is sown as soon as possible outdoors in cool winter areas as they require chilling to break their dormancy. Alternatively, place seeds in moist peat and sand in a plastic bag and leave them in the crisper of the fridge for 12 weeks before sowing in spring.
Named and selected forms of birch are usually budded or grafted onto seedling birch rootstocks. The weeping form B. pendula ‘Youngii’ is usually grafted onto 2–3 year old rootstocks at 2 to 3 metres high or at ground level and trained upwards with stakes.
Camellia: a magnificent evergreen shrub flowering from late winter through to spring suitable for acid soils.
Magnolia: stunning evergreen and deciduous shrubs to large trees with magnificent white and pink coloured blooms in spring or summer.
Azaleas: small to medium evergreen and deciduous shrubs with spectacular flowers in an array of colour combinations also suitable for acid soils.
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