“Trees are, quite simply, indispensable.”
HERE is what a tree can do: lower the temperature by 15C by providing shade and evaporative cooling with water transpiration from every leaf, provide food and shelter for wildlife including birds and insects, support pollinators such as bees and hoverflies, filter dust and air pollution, provide oxygen, support soil life through root activity, mulch and mychorrizal and fungal associations, allow winter sun through bare deciduous branches and filter water – including stormwater that is largely treated as a waste product in our cities – allowing it to percolate through to downstream water bodies and on to the ground water. Trees are, quite simply, indispensable.
You would think that extensive list was enough but in addition productive trees can also give us fruit, nuts, berries, edible leaves, bark, oil, resin and even sap (think Persimmons, Walnuts, Mulberries, Chinese Cedar leaves, Cinnamon bark, Olive and Eucalypt Oil, Mastic, Rubber and Maple Syrup) along with medicine, flowers, scent, Autumn colour and, of course, wood. And in terms of landscape design, they can give a signature style and theme, add structure, scale and definition to a garden, and are an essential layer of a Food Forest.
The longevity of trees is astonishing – the River Red Gum (Eucalyptus camaldulensis), indigenous to the area where I live in Melbourne, Australia, can live more than a thousand years – and even the Apple and Pear can live for a hundred years. When trees are allowed to grow to their mature size and shape – think of Botanic Gardens, old forests and pioneer homesteads where they are allowed to reach their full height and width – they are truly awe inspiring. However trees are disappearing with the increased pressure on our planet’s resources.
Forests are being cleared for agricultural and grazing land, and the small stock of trees in urban areas – fewer in the inner city and low-income suburbs – are being called on to serve as badly needed green space as our cities get denser and hotter. Local councils around Australia are putting together local Urban Forest Strategies as they recognise the vital role that trees – and vegetation layers in general – play in the health of the environment: the air, water, the temperature, and the support they give to humans and wildlife.
Closer to home, matching trees – and indeed any plant – to the conditions of your area is one of the most effective things you can do in terms of the success of a plant, its performance and ongoing maintenance. If you put a tree in a spot that’s not quite right – such as too close to a path or blocking a visual eyeline you want to keep – the time, effort and cost involved in removing it down the track can be considerable. Taking some time to think about your site conditions – boggy, sandy, intermittently flooded, shady, compacted and so on – is the key to what plants will do well there. There are a wide range of trees that naturally grow in all of these conditions and these will be your best performers.
There are exceptions: some tropical trees, for example, seem to have a wide tolerance and do surprisingly well in cooler regions while some coastal plants also display amazing tolerance for heavier clay soil. And weeds, of course, can adapt to all kinds of soils and conditions as an effective survival strategy. But if you are not working with a plant with a wide range of tolerances, you can use strategies such as creating microclimates to help plants thrive – think of the British monastic gardens of the Middle Ages with espaliered apples and pears against south-facing brick walls to capture the sun’s heat and act as heat banks. Creating a sheltered spot out of the wind can really help when it comes to plants that won’t normally tolerate your climate. I live in a temperate climate with distinct seasons – cold winters and hot summers: perfect for Mediterranean plants such as citrus but too cold for tropical fruit. Nevertheless, gardeners here are having success growing such tropical delicacies as Coffee and Sapotes. It can be done but requires nursing and sunny sheltered spots.
A much more robust and sustainable approach is researching a plant’s natural environment, or provenance, for vital clues as to the conditions it naturally does well in. Just as important is looking closely at local examples to assess their performance in the conditions you are up against. It can be as simple as: ‘Hmmm, that tree is South African and I know that plants from there generally do well in Mediterranean-type climates like where I live. I’ve also seen some of those exact trees thriving in my area. I think I’m on to a winner.’ And, importantly, plants that are indigenous to your area have spent millennia adapting and thriving in your local conditions.
A quick word about nursery tags and information from books or the internet that originate from overseas. The kind of site and climate-specific information you need is more detailed than what’s often written on a nursery tag and more specific to your local conditions than most information you will find online. There is no substitute for looking at examples of plants growing in your local area. In our experience, specialist nurseries will often be honest about which plants are hard to grow and what conditions they like – and don’t like. But even armed with knowledge, often people fall in love with tricky plants and go ahead regardless, although the rate of poor performance and plant death can be very high.
If your site is too hot, dry and unprotected to support the Silver Birches that you love, consider looking at planting trees that share their distinctive drooping fine foliage or bare white trunk that will thrive in your local conditions. Broadening your parameters of tree features – rather than sticking to a specific species – can help open up possibilities.
It is worth thinking about features such as height, width, shape, trunk, foliage texture, canopy density and colour before you plant as these will guide you to some great plants that will help create the look and feel of a garden, and act as important signatures to the overall style of your landscape.