Tree Selection and Establishment 

 

How to select the right tree for your garden?

Trees are an effective way to create a cool, comfortable garden. As hot air flows through the tree, the temperature drops as moisture evaporates from the tree’s foliage, and oxygen levels rise. It is important to make sure you select a suitable tree for your property, and your requirements.  

Before planting any tree, make sure it won’t be in the way of paths, the driveway, buildings or a clothing line, and that it won’t interfere with underground drainage pipes or overhead wires. Also think about how it can be best positioned for maximum summer shade effect. Planting a tree on the northern side of the house (or the southern side if you are in the northern hemisphere) will shade the interior rooms for much of the day; a tree on the western side will shade the house and garden when it’s generally most needed - the afternoon.  

Trees are the most important plants in your garden. They have a broad influence on the entire garden, not only from a design aspect, but also due to the effect the root system and canopy has on the smaller plants growing under or near to them. 

Learn more about the best trees for your garden here.

 
Why Plant Trees?
  • They provide protection from extreme environmental effects:
  • They keep the property warmer in cold weather and cooler in the heat.
  • They catch the rain and reduce the chances of flash flooding.
  • They slow the wind down in storms.
  • They produce life-sustaining oxygen.
  • They filter out dust and other pollutants from the air.
  • They provide shelter from the sun's dangerous ultra-violet rays.
  • They provide a source of firewood and timber for the construction industry.
  • They provide food, nesting sites etc. for birds, insects and animals.
  • They stabilise soil, which is especially important in erosion-prone areas.
  • They help drain water-logged soils.
  • Selecting a tree for your garden

    Deciduous and Semi-Deciduous Trees

    Many deciduous trees provide shade in summer and allow sunlight through during winter. Though these trees are grown mostly in temperate or even colder regions, there are some tropical trees which are deciduous or semi deciduous. Deciduous trees suitable for gardens include:

    •  Acer negundo (Ghost Maple) – A hardy, fast growing tree to 6-12m tall. The cultivar A. negundo ‘Aureo Marginatum' grows to 5-6m tall, and has attractive yellow edged leaves. The cultivar A. negundo ‘Variegatum’ grows to 5-6m tall, has very attractive white margined leaves. Any non-variegated shoots should be removed as soon as they appear for these two cultivars.
    •  Acer palmatum (Japanese Maple) – A lovely small tree for the garden. Grows up to 6-8 m tall. Many varieties are available that display different leaf colours and shapes. Autumn foliage is best in cool areas in full sun. It has a fibrous root system that rarely causes problems.
    •  Betula pendula (Silver Birch) – A tall, narrow tree with attractive peeling white bark and small, dainty leaves. Close planting helps to keep the trees small; often closely planted in triangular groups of three. Needs moist soil and a cool to cold climate.

    • Bauhinia variegata – A small tree reaching 5-10 m. Large orchid-like white or mauve flowers in early spring. It mayneed shaping to develop a tree-like form. It grows in a range of climates, but is only fully deciduous in cold areas. 
    • Calodendrum capense (Cape Chestnut) – Grows to 8-15 m with a broad crown. Profuse clusters of pink flowers in mid to late spring. Fully deciduous in cooler climates and areas with dry winters; evergreen elsewhere. 
    • Caesalpinea ferea (Leopard Tree) - Medium sized tree to 6m with leopard-patterned bark. Showy yellows blossoms appear in spring. Best in tropical and subtropical areas.
    • Caesalpinia pulcherrima (Pride of Barbados) – A medium shrub to small tree (up to 4 m). It has attractive red and yellow flowers in summer and autumn, and fern-like foliage. It needs pruning in its early years to shape it into a tree form. A good shade tree for small gardens in frost-free areas (tropics and subtropics).

    Cornus florida (Dogwood) – A small to medium tree, 4-9m tall, with layered, horizontal branches. Pink 

    or white bracts appear in mid spring followed by red berries and colourful autumn foliage. Needs moist soil and a cool climate. An excellent feature tree.

    • Delonix regia (Poinciana) – Grows to 10 m tall but has a much broader spread. It has bright red flowers in late spring. It has an attractive broad canopy so it needs lots of space to spread. An excellent shade tree for subtropical and tropical areas only.
    • Fraxinus excelsior ‘Aurea’ (Golden Ash) – Grows to 6-12m tall, with its spring and autumn foliage being golden yellow. It is also attractive in winter when its yellow-gold younger branches can be easily seen. Lower side shoots should be removed as they appear to promote a tree-like shape when the plant is young. A pendulous form is also available, and this is grafted onto seedling root stocks at a suitable height.
    • Fraxinus oxycarpa (Desert Ash) – Grows to 10-15m tall, and is fast growing, and generally hardy in hot, dry conditions. Superior forms budded on to seedling root stocks are available.

    • Ginkgo biloba (Maidenhair Tree) – A narrow, slow-growing tee to 15-25m tall with beautiful lime-green ‘maidenhair-fern’ foliage that turns yellow in autumn. Tolerates pollution but needs a large garden. Needs mild to hot, moist summer and cold winter. Caution: fruits smell of carrion.
    • Jacaranda mimosifolia – Grows 10-15 m tall and has a broad crown. Showy mauve bell-shaped flowers in spring and fern-like leaves throughout summer. Fully deciduous in cool to mild areas; retains some foliage in warm climates.
    • Koelreuteria paniculata (Golden Rain Tree) - Fast growing and hardy tree to 12m with a broad canopy. Small yellow flowers are produced in panicles in late summer followed by inflated red capsules through to autumn.
    • Laburnum anagyroides (Laburnum) – Slender, vase-shaped tree 6-8m tall. Showy golden pendulous flowers in spring. Needs a cool to cold and moist climate. Can be trained over arches and as an espalier against a wall.
    • Liquidamber sytraciflua (Liquidamber) – A large tree to 20-30m tall, with a straight trunk and a pyramidal shape. Grows well in mild to cold climates but only develops a good autumn display in cool areas.

    • Quercus spp. (Oaks) – Tall trees which are best suited to larger gardens. Good autumn display in cool climates (especially the Pin Oak, Quercus palustris). Tolerates warm, hot summers but needs cool winters. 
    • Robinia pseudoacacia (Golden Robinia) – Grows to 10 m tall and 8 m wide. Can be fast growing in good conditions. Attractive lime-green foliage turns golden in autumn. Roots can be a problem, as can suckers
    • Tabebuia spp. (Trumpet trees) - Grow around the 6-12m height range with a number of different species well suited to the subtropics. Colours of flowers are yellow, pink or mauve in clusters during spring or summer. Most are attractive shaped trees.

     

    Evergreen Trees

    Many evergreen trees provide year-round shade. The following selection is only a small sampling out of thousands of good options:

    • Arbutus unedo (Irish Strawberry Tree) – Dense medium tree 6-8m tall with dark green leaves. Insignificant flowers are followed by strawberry-like fruits. Hardy in cool climates.
    • Ceratonia siliqua (Carob) – A hardy, adaptable, small tree to 5-6m tall, with attractive, compound, dark green, leathery leaves. It has small, reddish flowers followed by masses of pods which are a valuable source of nutrients (sugars and proteins) for both stock and humans. It is very drought resistant.

    • Eucalyptus ficifolia (Red Flowering Gum) – Small to medium eucalypt to 12m tall with a broad canopy and short thick trunk. Showy red or pink flowers in summer. Attractive small shade tree for mild to cool areas with drier soils.
    • Gordonia axillaris (Gordonia) – A small tree or large shrub to 7m tall. Showy white flowers in autumn, similar to camellia flowers. Tolerates some shade. A good lawn specimen or screening plant for moist, deep soils in temperate to cool climates.
    • Harpullia pendula (Tulipwood) - Dense tree to 10m when grown in most gardens. Dark green shiny leaves highlight the red fruits and black seeds that attract birds.

     Ilex aquifolium (Holly) – evergreen, much branched tree, usually erect. Height 20m and spread 6m. Frost hardy. Variably shaped, wavy, sharply spined, glossy, dark green leaves and bright red berries. Needs male and female trees to produce berries.

    • Michelia champaca (Himalayan Magnolia) – Conical light green foliage tree to 15m with scented yellow-orange flowers in late summer.
    • Pittosporum undulatum (Native Daphne) – Small tree to 6m but dense and wide. Leaves are wavy-edged and scented white flowers are produced in spring.
    • Prunus lusitanica (Portugal laurel) – evergreen, dense, spreading tree growing to 6-10m high and wide. Reddish-purple shoots with glossy dark green leaves. Slender spikes of fragrant white flowers in early summer followed by deep purple fruits.
    • Schinus molle (Pepper Tree) – Grows 8-10 m tall and nearly as wide – needs plenty of space to spread. A graceful tree with pendulous branches and fine leaves. Grows well in hot dry climates; also does well in cooler areas but does not like heavy, wet soil.

    Spathodea campanulata (African Tulip Tree) – Grows to 12-20 m with a broad canopy of 8-15 m. Has showy orange-red flowers in autumn and winter. Suitable for subtropics and tropics.

    • Syzygium sp. (Lillypilly) – Medium to large trees with dense crowns and glossy dark green leaves. Fluffy white or red flowers followed by white, red or purple fruits. Very adaptable with some species growing well in temperate, subtropical and tropical areas.

    Learn more about trees here.

     

    Tree Health

    Lack of proper attention given to trees (and for that matter, shrubs) early in their life can result in problems later on:

    • Splitting and loss of branches due to weak joints
    • Large sections of rotting wood
    • Poor shape or form
    • Poor flowering or poor autumn foliage
    • Whole trees or parts of trees threatening to fall and creating safety hazards
    • General reduction in the lifespan of the tree.

     

    Trees can die through many different problems: diseases, pollution, fire, environmental extremes (too hot, cold, water excess or deficiency etc.), insects, animals and the activities of humans. The main cause of problems in trees, though, is micro-organisms which enter the tree through wounds; this leads to gradual but eventual rotting away of the wood.

    Wounds can occur in many different ways:

    • As a knock from a lawn mower
    • Insects or animals damaging the tree
    • Breaking a piece off the plant instead of cutting it
    • Branches blown off in storms
    • A stub from a fallen branch that does not properly heal.

     

    Trees which are healthy and growing vigorously are usually far more capable of resisting disease and repairing damage when they are wounded. A healthy tree will usually seal off infection by "compartmentalising" it (i.e. locking it into a compartment so the tree grows around the affected wood). 

     
     
     
     
     
     
     

    To keep trees healthy, do the following:

    1. Avoid wounding. If necessary, protect trees with fencing or a guard. Be careful when working near a tree.
    2. Keep trees well watered and fertilised. Older, fully-grown trees respond very well to annual or biennial feeding, and to being well watered at least twice over the dry season.
    3. Don't cultivate around the base of a tree – this can damage roots.
    4. Keep pedestrian traffic away from the base of a tree. This causes soil compaction.
    5. Treat wounds as soon as they occur or are noticed (i.e. cut out disease back to clean wood using a sharp tool; cuts should be neat and clean.) Tree wound paints can be used, though they are not necessary.
    6. Avoid spilling chemicals, salt, beer or detergents around the base of trees.
    7. Remove injured or diseased branches. Prune back making a clean cut, at an angle of 45 degrees to the horizontal so that water will not sit on the stub. Leave a slight stub and don't cut flush with the trunk or main branch.
    8. Practice sanitation. Keep diseased wood away from trees. Tools should be clean and the general area should be as free as possible of pest and disease which might affect the tree.

    Supporting Trees

    1. Only stake trees if absolutely necessary – staking comes with its own set of problems i.e. damage from rubbing or girdling by stakes, stress at the point of attachment to the trunk which may cause the trunk to break, inappropriate growth patterns i.e. bending away from the stake, cause wind resistance if the crown can’t move which may cause breakage once the stake is removed, die back of trunk or branches, develop less trunk taper, increase the height but with less trunk thickness).
    2. Trees under a certain height and diameter don’t need staking i.e. less then 2 metres tall and 2.5cm diameter.
    3. Trees only need staking when they root system cannot support the tree in an upright position. The ability of the tree to do this will depend on the site, soil texture and moisture and exposure to wind. Plant the tree and check for movement before staking. Holes created at the base of the trunk above the root system indicates that staking is required, or if the tree starts to lean.
    4. Stakes should only remain in place for just long enough to enable the tree to develop a strong root hold into the soil and supports itself.
    5. Don’t stake too high – stake should be 1/3 of the length of the tree (and certainly not more then 2/3 of its length).
    6. Don’t tie too tightly.
    7. Use flexible material as ties and allow movement down the trunk to assist in correct taper development.

     

    Tying Trees

    Tree tying also refers to training branches to grow in certain directions. In fruiting trees this can be achieved by attaching weights to the branches to encourage downwards growth. In espaliered trees this can be done to achieve patterns of growth and in roses in is done to encourage the development of more flowers.

     
     
     

    Suggested Reading

    The following e-books have been written by the principal and staff of ACS Distance Education.
     
    We have developed and published these books to specifically complement the courses which the school offers. These books are all "stand alone" references though; and just as valuable a resource whether used with or without a course.