The sun shone on Melbourne’s gardens in May – and kept shining. Warm-weather plants that had begun to die back in expectation of winter got a second wind. Basil started sprouting leaves again and roses shot new buds. The state’ssecond-warmest May on recordalso confounded cold-weather plants starting to make their way out of the ground. Was it time to bloom or sink back underground?
Meanwhile, in the state’s south-west, dry earth became even drier, andraised the risk of unseasonal fire. At the same time, in coastal parts of New South Wales and Queensland, it didn’t just rainbut it poured.
So as the seasons become more erratic and the climate crisis results in observable changes to our gardens, how should green thumbs respond? How do we know what is going to grow well – and how can we plan for our future gardens when it feels like the old rules no longer apply?
There isn’t “a clean, crisp answer” to this question, says Prof Angela Moles, a biologist who heads up the Big Ecology Lab at the University of New South Wales. The lab’s mission is to find out how Australian plants are responding to the climate crisis and quantify the factors influencing those changes.
“Different parts of Australia are changing in different ways. Often the dry parts are getting drier and the wet parts are getting wetter, and different species are responding to things very differently,” Moles says.
Primarily, they’re responding by shifting their distribution. Often that happens in counterintuitive ways, with more than a third of plants moving “backwards”, such as towards the warmer areas where they might be thought to prefer cooler ones.
“We’re seeing a lot of reassembly starting to happen, and the speeds at which species are shifting are quite frightening,” Moles says. Globally, plants are altering their range at a rate of about 800 metres per year, mirroring what we know about plant behaviour from the previous ice age. “Everything’s in this wild state of flux.”
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Around Australia, plants are also changing the way they grow, such as when they flower, when their leaves come out, when they germinate or come up from the ground. That poses particular challenges for horticulture and conservation.
“There are cases where species start flowering earlier, but their pollinators [such as insects and birds] aren’t around yet, or their pollinators are coming out even earlier. Pollinators are changing more quickly than the flowers, and that’s causing some mismatches,” Moles says. Some of them, too, are going extinct.
All this underscores the need to alter gardening and landscaping choices to take into account changing plant behaviour in response to the climate, but it also makes planning for that unpredictable behaviour very difficult.
Clare Hart, the director of horticulture at Melbourne’s Royal BotanicGardens, says her team has been working on precisely this problem since 2016, assessing species for climate risk and developing a succession strategy for the gardens’ future.
“We’re working towards [a projected climate of] 3C warmer, and also [we’re] going to have less rainfall … So the plants that we need to grow are from warmer, drier climates,” Hart says. “We focus on adaptation because mitigation just isn’t happening fast enough. And anything we do in an adaptation space will also assist with any mitigation when it does happen – and it needs to happen.”
In 2018, the gardens held an international climate change summit, out of which sprung the international Climate Change Alliance of Botanic Gardens. One practical tool developed by that alliance to help with planning, especially for trees, was theclimate assessment tool. Available to the public, the tool models the likely suitability of different tree species for a specified location against projected climate scenarios.
A new feature of the gardens, the Australian Drylands is “essentially a great experiment” to assess which native plants might grow well in a warmer, drier Melbourne. Horticulturalists looked north, from the top of NSW across to Western Australia, and collaborated with traditional owners, parks workers and other botanical gardens to understand which plants might suit the coming new normal further south.
Hart names kangaroo grass, flame trees, spear lilies, gymea lilies and cycads as just some of the more well-known varieties already showing their versatility and resilience.
Look local: what’s thriving around you?
Moles and Hart recommend walking around your neighbourhood and taking note of the plants that are flourishing, especially if they’re native, and where in the garden they are placed.
Planting out your nature strip can be a great way to help local ecosystems become more climate resilient, says Moles, as it helps mitigate urban heat pockets, provides habitat and assists in migration routes for plants, birds, animals and insects.
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Consider your microclimate
Regardless of where in Australia you live, it helps to learn a bit more about the specific needs of plants, and what you are currently providing them with. “Understand your soil conditions, understand water, where it comes from, and if you have the opportunity to put in a water tank – things like that really will help you to future proof,” says Hart.
Recognise also that “your microclimate can change quite dramatically, even from neighbour to neighbour,” Hart says. If your garden space is a balcony with a lot of afternoon sun, that may be better suited to growing plants more commonly found hundreds of kilometres further north than those thriving in next door’s shady back yard.
Consult local experts
Hart recommends smaller, local nurseries and Indigenous plant nurseries as good sources of knowledge about plants that will do well in local conditions. Local councils will also often have local plant lists and resources for home gardeners who want to build local habitat. Connecting with community groups can be a useful way to learn about what’s doing well in nearby bushland areas.
Give plants extra protection when they’re young
Plants are most vulnerable during their early establishment phase, so try planting them in a context that allows you to give them a bit more care and attention while they’re starting out, says Moles. “Once they’re established, they’ll be a little bit more robust.”
Use free tools and resources
The Climate Change Alliance of Botanic Gardens’climate assessment toolcan help you find out if the tree you want to plant is likely to thrive or struggle under future climate conditions.
Which Plant Wherehas a database searchable by location and plant type, and allows you to filter results for different types of gardens and plant needs for estimates of climatic suitability in 2030, 2050 and 2070.
TheAtlas of Living Australiapulls together Australian biodiversity data from multiple sources. Explore your local area and find out to show what plants are growing around you (and which animals have been seen locally, too).
The Bureau of Meteorology provides general forecasts for rainfall and temperatureup to four months in advance, giving you a rough idea of what conditions are likely for the season ahead.
School of Thumbis a horticulture industry-funded video series aimed at less-experienced gardeners, to help them think about their circumstances and the plants that might suit.