2019 was Australia’s hottest and driest year on record. Studies show trees can significantly reduce temperatures beneath their canopy and act like nature’s air conditioner.
So we need to plant more trees, particularly in urban areas as our cities and towns trap more heat than surrounding rural areas.
As temperatures continue to warm, choosing the right tree for the right place is critical.
The wrong tree in the wrong place may shade out valuable winter sun, invade your drains and cost thousands to remove.
Before you buy a tree be clear on the role you want the tree to play in your landscape. Do you want it as a feature only or will it provide much needed summer shade and winter sun to your outdoor haven or micro-oasis or will it form part of a windbreak to the west?
In built-up areas, consider how planting a tree will impact your neighbour’s home and garden – it’s not fair to shade out their much needed winter sun if you live in temperate parts of Australia.
Not all deciduous trees lose their leaves in Autumn. Some hold onto their leaves into early Winter when you want winter sun to penetrate into your outdoor haven and home. If possible, purchase deciduous trees in Autumn. Visit nurseries and check out not only individual tree colour but when individual specimens start to lose leaves. Or you can engage the services of a plant broker to source your trees.
Trees vary considerably in their growth rate – one of the simple rules of thumb, is the faster they grow, the shorter they will live. If you have enough space in your garden, consider growing short lived trees, that live to 20 years, like Melia azederach plus longer lived species, like the Cork oak, Quercus suber.
By 2050, it’s reasonable to assume that the climate in southern Australia will have temperature increases of 2 degrees Celcius and increased drying of between 10-20%. While by 2090, if emissions continue unchecked, inland places like Canberra will have temperature increases of 4C and potentially up to 25% less rainfall. (Assumptions are based on the Climate Analogue Tool using highest emissions scenario and selecting ‘hottest and driest’ scenario.)
I’ve selected the following trees for Canberra, based on research by the Australian National University that ranked trees based on their ability to cope with a hotter and drier climate. The following seven trees can all cope with drought and frost once established – five are deciduous and two evergreen.
Lagerstroemia indica x L. faurieri – Crepe Myrtle
While many trees struggled or died over summer heatwaves in 2019/20 in Canberra the Crepe Myrtles looked good. There are a number of cultivars within Fleming’s Indian Summer range, including ‘Biloxi’, ‘Tuscarora’, ‘Osage’, ‘Sioux’ and ‘Natchez’.
‘Sioux’ is one of the smallest, growing to around 4 metres high x 3 metres wide and ideal for a small outdoor space or in a large pot on a balcony.
I’ve planted three Lagerstroemia indica x L. fauriei ‘Tuscarora’ in my north facing courtyard in Lyneham. These trees are broadly vase-shaped and multi-stemmed and will grow to between 5-6 metres high x 4 metres wide. I’ve planted them so they will eventually overlap and provide summer shade over our small outdoor haven (a diminutive 4 x 8 metres).
Crepe Myrtles have mottled trunks and can become a feature in a small space. In the ‘Tuscarora’ cultivar this patterning is revealed at around three years old when the bark starts to exfoliate. These trees don’t like wet feet so it’s best to build up the planting hole with topsoil if your soil is a heavy clay.
‘Tuscarora’s’ leaves turn a reddish bronze colour in Autumn and mine lost most of their leaves by winter’s start.
Keep this tree happy by applying a complete fertiliser in spring and giving it a deep soak during hot weather.
Gleditsia triacanthos ‘Sunburst’ – Honey locust
If you are keen on golden hues, this might be the tree for your outdoor space. This deciduous tree has moderate to fast growth rate with a rounded form and pendulous branches.
‘Sunburst’ is a non-thorny form and exhibits yellow-green foliage in summer which turns yellow in Autumn. The tree grows to around 8 metres high x 8 metres wide and prefers well drained soils and full sun.
Honey Locust originates in central and eastern USA and can tolerate frosts to -10C. Avoid disturbance around the base, otherwise it has a tendency to sucker. It’s recommended to plant at least 5 metres from building footings.
Liquidambar styraciflua ‘Tiriki’ – Sweet Gum
Liquidambar ‘Tiriki’ is a long lived upright tree with a medium growth reaching 10m high x 8m wide. Copes with extreme cold (to -10 Celcius) and hot conditions. ‘Tiriki’ is a Canberra cultivar. Liquidambar naturally grow in the Eastern USA and Mexico.
Liquidambar exhibit pretty Autumn in the orange-red range. Some trees hold their leaves for a long time and into winter. If you are considering this tree, check when they lose their leaves.
Melia azedarach ‘Elite’ – White Cedar
White Cedar is a fast growing native deciduous tree that originates from NE Australia and SE Asia. The fruit of Melia azedarach are poisonous to humans and some animals – hence the cultivar ‘Elite’ was selected because it is fruitless.
In Canberra, Melia azedarach ‘Elite’ grows to a similar height and spread to Liquidamber ‘Tiriki’ – around 10m tall by 8m wide. Glossy green foliage emerges in spring along with fragrant lilac flowers. Autumn foliage is golden.
Ulmus parvifolia ‘Emer II’ or ‘Emerald Vase’
- Ulmus parvifolia is an elegant medium-sized deciduous tree. You will need a decent sized garden for this beauty as it grows to around 13 metres high x 10 metres wide. This tree is long lived with a moderate growth rate. It has decorative bark and the green foliage turns yellow in Autumn.
Brachyciton populneus – Kurrajong
This is a sturdy evergreen Australian native with green glossy foliage. It grows relatively slowly and may only reach 4 metres high in 10 years. I recommend using this tree as part of a windbreak or where winter sun is not required.
I’ve successfully grown this tree at the Banksia St, O’Connor wetland.
Quercus suber – Cork Oak
- Quercus suber is a slow growing and long-lived evergreen tree with some specimens living to 200 years. It was originally grown for its corky bark used in insulation and for corks for wine bottles.
Cork Oak is native to south western Europe and can grow to 15m high x 10m wide.
I would recommend this tree for large urban and rural blocks.
Check out my 4 week online course – “Getting started – learn how to design your own cool outdoor haven”
7 steps to create a cool outdoor haven
Summer 2018/2019 was Australia’s hottest summer on record and temperatures have risen by over 1 degree since records began in 1910. It’s likely most of Australia will be hotter and drier in the future.
Many Australian homes are poorly designed and don’t consider the local climate.
Wherever you live, there are many things you can do to create cool outdoor spaces that improve your health and well-being. Studies shows the more contact with nature, the better we feel.
Whether you own a home or are renting, creating a cool haven adjacent to your place will keep you cooler on hot summer days and nights.
Plants play a key role in keeping our gardens and homes cooler and viewing bright green leaves feels uplifting when the surrounding landscape is yellowed. Thermal imagery demonstrates trees can reduce surface temperatures by as much as 10 degrees.
Here’s 7 points to consider when creating a cool outdoor haven.
Find out more about your local climate – for example, Canberra has a climate of extremes – hot dry summers and cold winters. In Canberra, the emphasis should be on maximising summer shade and in winter maximising sun. Temperatures of -7C in winter are not unusual. This will influence the trees you grow – in most situations, deciduous trees will be most appropriate.
Assess the soil on your site. Is it clay, loam, rocky, mainly sand or other? Aim to amend existing soil not remove it. Ideally you want to turn your existing soil into a sponge that can absorb water and carbon – the best way to do this is to start composting your household’s food scraps. Once they are broken down you can incorporate them into the soil. If you are low on space, a bokashi bucket is small enough to fit into a kitchen and breaks down material with no odour.
Add locally sourced organics like fallen leaves, coffee grounds (plenty of cafes bag these up each day) and manure. And use a thick mulch (75-100mm depth).
If you live in a dry climate, irrigation is critical to creating a lush outdoor space, however, check out the water restrictions in your local area. If you own your own home, consider installing rainwater tanks or building a grey-water treatment system.
The most efficient way to irrigate is to use drip irrigation rather than sprinklers. Other options include the use of wicking beds or sub-surface irrigation using water harvesting. If you use grey water from the shower or washing machine, choose cleaning products that are safe for the garden and avoid splashing edible leaves with grey water as it can contain E.coli.
Ponds can create a cooler feel and the sound of running or spraying water is soothing. For renters and apartment dwellers create a pond in a large pot with a number of wetland plants and gold fish. Including a pump will reduce the likelihood of mosquitos and algal build up. Gold fish provide splashes of colour and are a tough low-maintenance pet.
Well-designed in ground ponds will provide habitat for frogs, dragonflies and birds will enjoy bathing in them in hot weather. Insects can drown in buckets of water or deep ponds so provide shallow saucers filled with water and gravel to give insects like bees and lady birds a drink.
If you are creating a potted haven, think about how you will keep your plants watered in hot weather? Containerised plants dry out very quickly in hot weather and may require watering twice a day. Check if there is a tap handy. Using wicking or self-watering pots help ensure plants stay watered at their roots.
If your only option is to garden in containers follow these steps for a greater chance of creating a great outdoor space that you want to hang out in.
Repurpose or buy the biggest container you can for growing shade trees. The minimum pot size for a tree that’s around 1.5 metres tall would be about a 40cm diameter. Think about the weight of the pot too, will you be able to move it around once it has soil in it?
Buy quality potting mix and look for the Australian Standards tick of approval on the side. Use water holding crystals to trap moisture near the plants roots.
Choose plants appropriate for your area and consider multiple functions of plants – if you are choosing a tree consider: will it provide shade in summer and allow sun through in winter, does it bare fruit and does it have flowers attractive to pollinators?
Consider incorporating a ground-cover around the base of your tree. When the ground-cover begins to wilt – investigate if the potting mix is dry. The best way to test this is with your finger.
Mulch your plants – mulch reduces the amount of water evaporating from the pot. Make sure you move mulch aside to checkwater has penetrated below the mulch into the potting mix.
Choose plants that can cope with a hotter, drier future. Check out climate model projections for your area. Climate modelling shows Canberra’s climate in the future will be more like Dubbo and Gilgandra – a 4.5 hour drive north of Canberra.
Choose layers of plants – groundcovers, climbers, shrubs and trees – this will help create lots of evaporative cooling in the garden.
In order to create a lush feel around your home – consider incorporating plants with large green leaves. These might be plants you can grow in your pond in sight of your living area.
Incorporate seating into your outdoor space – a place to unwind, sip on a favourite drink, observe wildlife and interact with those you share the house with. Leave your phone, ipad or laptop inside – this is time to unwind.
Seats don’t need to be expensive – an upturned crate with a cushion can provides a great place to perch.
- Outdoor cooking
One of the best ways to keep your home cooler on hot days is to cook outside. Alternatively, ditch the cooking and make a salad or a Buddha bowl.
Community funds micro-forest
The Climate Factory and the Downer ParkCare group raised $20,000 to build a pilot micro-forest at the Cole St park in Downer. Over 180 individuals and businesses supported this initiative.
Edwina Robinson, Landscape Architect and Founder of The Climate Factory says, “planting trees is one of the simplest things we can do to address hotter, drier climates. Trees cool the environment, provide habitat, absorb carbon and improve property values.”
The $20,000 raised will pay for community engagement, development of a Landscape Sketch Plan, soil improvement, 1500 climate-ready native trees, shrubs and groundcovers and a water cart to keep plants watered during the establishment phase. The Downer ParkCare group will maintain the space and will have a say about other features they’d like to see in the park.
Robinson formed the social enterprise, The Climate Factory, in 2019 after Canberra experienced its hottest summer on record. She says, “Bureau of Meteorology records show January 2019 temperatures for Canberra were 6 degrees above average. I knew I needed to do something. So whenever I think, why the hell am I doing this, I remind myself I’m doing this for my adult children and my unborn grand-children”.
Robinson says she wouldn’t have had the confidence to launch her social enterprise and Crowd Funding campaign without the support of the Mill House GRIST program.
The Climate Factory will work with tree and native plant experts to create a climate-ready plant list for a public space. They will choose plants with low flammability and that can cope with hotter, drier weather.
Native plant nurseries will start growing plants before the end of the year with the first planting day scheduled for April 2020. Robinson says “hopefully it will be a mild Autumn and plants will get a great start”. Supporters who pledged $25 or more will be invited to the first planting day in 2020.
In October 2019, Robinson and Lachlan Richardson, Bluebell 2509 installed a micro-forest of 300 native plants across the road from the Cole St Park. They are looking forward to working with the Downer community to watch both micro-forests grow.
The Climate Factory is looking for partners and sponsors to build a micro-forest in a school in one of Canberra’s urban hot spots in 2020. Robinson says, “The Climate Factory will use land surface temperature maps created by CSIRO to help work out which Canberra schools need micro-forests the most. We will work with students and teachers so they can learn about the values of forests and together design and build a micro-forest and show them how to maintain it.”
Service One, a 100% community owned bank, kicked off the fundraising with $5000. The other official sponsors are:
Gold Sponsors $1000
Light House Architecture and Science
Silver Sponsors $500
Bronze Sponsors $200
The Tree Man
Canberra Magic Kitchen
Robyn van Dyk
The Silver Birch is dead
In 2010, I bought a Canberra fixer-upper with no garden to speak of. The front garden boasted two non-fragrant roses, an oleander (despised from my childhood) and a Liquidamber street tree.
As a young Landscape Architect student I was besotted by Edna Walling. Acclaimed as Australia’s first landscape architect, Walling was an unconventional woman. She ran a landscape design and construction business from the 1920s , built her own cottage and created an English style housing development in Victoria, named ‘Bickleigh Vale’.
The first essay I penned at the University of Canberra was about Miss Walling’s design style. English born, she determined the location of Silver Birches by scattering potatoes on the ground.
With a new garden to design and plant on a budget, I decided I wanted a grove of white trunked Silver Birch (Betula pendula). Underneath I would grow rosemary and Grevillea. Note: the rosemary (tough bugger that it is, thrived) but the Grevillea ‘Deua Flame’ died one by one.
Birches have a reputation for thirst – but the Millenium Drought was over and I knew I could gravity feed water from an upstairs bathroom, if needed.
That Autumn, after removing the roses and oleander and the patchy grass, I planted nine $20 birches into compost enriched soil. I wasn’t as flamboyant as my hero, Walling, the birches were planted in evenly spaced trios.
Three years and a few wet seasons later, the Birches thrived. Lying in my upstairs bedroom I could glimpse their canopies and marvel as the Rosellas performed acrobatic feeding acts dangling from drooping branches.
But success was short lived.
Those nestled close to the house or large shrubs thrived. However, the Birches abutting the western side of the block with its hard, hot drivewayof concrete and bitumen and nothing to buffer blasting summer winds, fared poorly. Their trunks were only half the diameter of the happy ones.
In the back garden, I planted three tubestock of Snow Gum (Eucalyptus pauciflora). They grew quickly to about four metres high, and after a couple of very dry summers I was left with one survivor. Snow Gums suffered a similar fate at the nearby Banksia St, O’Connor wetland where planting commenced in 2010.
Records from the Bureau of Meteorology show that Canberra’s summer of 2018-2019 was the hottest on record. The Birches branches browned.
This year, nine years after planting, I removed three of them, and sold the house.
Temperatures in Australia have risen by at least 1 degrees celcius since 1910. And we know Canberra’s future will be hotter and drier with more extreme events, including heatwaves and intense rainfall.
Temperatures will not only impact the types of trees we can grow in Canberra in the future but our ability to stay fit and well.
Increasingly evidence shows high temperatures result in increases in violence and mental health presentations. And who wants to exercise when it’s extremely hot? This will no doubt impact obesity levels and associated preventable diseases, like diabetes.
Unfortunately we’ve lost a significant number of trees in Canberra over the past few years and it’s vital to boost our tree canopy with climate-ready species. Note: the ACT Government committed in the 2019 budget to plant 17,000 trees over the next four years.
As I cycled round Canberra in Autumn 2019, I noticed one stellar deciduous tree – the Crepe Myrtle (Lagerstroemia) with its motley bark, multi-trunked stems and vibrant flowers was a stand-out.
Another, under-celebrated tree, the Kurrajong (Brachyciton) has proven to be a great performer. At Banksia St wetland, young plants were attacked by cockatoos (the vandals of the bird world). Those that survived are robust and beautiful.
Creating climate-ready public spaces and gardens will help us thrive in a hotter, drier future. The ANU has been working with the ACT Government to develop a list of trees suitable for public spaces for changing conditions and CSIRO has developed heat maps to identify areas at most risk of heat exposure with vulnerable populations. There are sections of Belconnen, Gungahlin, Molonglo, Tuggeranong, Weston Creek and Woden where communities are at significant risk. No surprises, that if you live near Lake Burley Griffin you will probably be ok during heatwaves.
The CSIRO report recommends planting vegetation and forests in our public spaces, streets and parks as one of the main ways to mitigate future heat. Plants have a more significant cooling effect if we can find ways to irrigate them, using water harvesting.
As a result of the hottest, summer on record I knew I needed to act. So The Climate Factory, was borne.
The Climate Factory is a social enterprise, that designs and builds micro-forests, to ensure we thrive physically and mentally in a hotter, drier future.