Building a climate-resilient garden
With extreme weather predicted to increase in a warming world, it’s wise to plan ahead. Horticultural experts share what you can do to still have a productive and beautiful garden.
Record-breaking rainfall, floods, bushfires, heatwaves and drought have made gardening more challenging than usual. One organisation at the forefront of helping us adapt our gardens to be more resilient to environmental stress is Australian garden charity, the Diggers Foundation.
CEO Tim Sansom reveals that Diggers has been busy forecasting what climatic and environmental conditions gardeners of the future will have to deal with, pressure-testing plants and applying age-old horticultural practices. “We go to the past, but look to the future,” he says. “If you’re planting a tree, for instance, you’re going to be looking at the next 50 to 100 years for that tree to live.”
Australian government website Climate Change in Australia forecasts sea level rise, higher average temperatures across all seasons and an increase in hot days and drought across the nation. While predictions vary from region to region, most areas will also experience greater bushfire risk and more frequent extreme rainfall events.
Sansom, who also has an extensive background in environmental management, sustainability and food production, says it is pushing the tolerances of plants beyond their limits of a generation ago. “Anything that was written around Australian gardening for the last generation is becoming less relevant,” he says. “We’re getting massive fluctuations in weather events. We have to design gardens to survive those extremes.”
A two-degree increase in average temperature might not sound like much, but it is a massive shift in terms of the extreme end of weather, he says. “Most plants have an extreme level limit. The more of those days we have, the more those plants are going to die.”
Drought and heat
About 80 per cent of the Australian population and most New Zealanders live in a temperate to Mediterranean climate, Sansom says. “Much of our plant palette has been crafted for low rainfall. That’s the dominant problem in the Australian landscape.” In fact, Australia is the driest inhabited continent in the world.
The Diggers demonstration gardens provide examples of plants that can survive drought and other stressed environments and how they can work in combination. Drought-hardy plants include the sedums (perennial plants with flowers and a succulent form virtually unkillable in heat), salvias and silver-foliage plants like wormwood, he says. “There’s a vast array of other Mediterranean perennials, all of which will take dry, hot summers. Those that are herbaceous (die down in winter), have cold tolerance as well.” edibles that suit this range include figs, caper bush, bay, feijoa and anything that grows in a desert environment of extreme heat and cold, Sansom says.
Jonathan Garner, author of Dry Gardening Australia, a consultant horticulturist and fellow of the Australian Institute of Horticulture, says the foundation of a water-efficient garden is healthy soil. Incorporate organic matter and avoid synthetic fertilisers and pesticides — these kill soil microorganisms vital to healthy plants, he says.
To reduce water evaporation and soil temperature, mulch beds using natural materials such as straw, pine needles, bark, woodchips or (in shady spots) rocks, he says. Weed out water competition from grass and weeds in beds and around trees. Prune dead foliage to reduce transpiration from leaves, he adds.
Another ally is shade. Build it using other plants and structures like trellises and arbours, but be aware that most plants still need sunlight, he cautions. Move potted plants into shade. Throw shade cloth over food crops and precious plants.
Ideally, water between 6 and 8am, Garner continues. With the plant coming into its most stressful time, this prepares it for the day. “The leaves will dry quickly and water is absorbed with less evaporation during the cooler parts of the day.”
Water less regularly but more deeply. This encourages deeper, more extensive root systems, which improves the plant’s drought resistance, Garner says. How much and how often you need to water depends on the soil’s water-holding capacity, plant rooting depth and weather conditions. As a general rule, he advises irrigating until no more water soaks into the soil.
Alternatively, install drip irrigation. It results in less water loss and maintains more constant soil moisture, Garner says. Specially constructed raised garden beds watered at the base (wicking beds) are another popular solution for dry conditions.
Avoid planting new trees and shrubs or laying turf during summer. And, when planting, dig as deep as possible and break up compacted areas to encourage root penetration.
Mow turf less frequently and raise the cutting height 25 to 50 per cent during drought periods. Garner says, “Mowing stresses the grass by increasing respiration and reducing root growth.” Leave clippings and leaves on top as a mulch.
Focus on growing perennials as much as you can. Annuals and vegetables require lots of water, he says.
View this post on Instagram
Extreme wet
Paradoxically, global warming trends mean that along with reduced overall precipitation, Australia will get slammed with more frequent intense rainfall events. La Niña weather patterns, which contribute to cooler and wetter conditions, can intensify this.
Permaculture teacher, consultant and eco-developer Ian Lillington says the effects on plants can include injury to stems, leaves and roots, wilting, decay, compacted soil, soil erosion and bacterial, fungal and viral diseases. Diverting water away to prevent water logging and improve drainage is key, he says. Read the landscape, slopes and the direction water is running and pooling in. Raise the height of garden beds and plant trees on slightly raised areas. When that’s not possible, bank earth around the bottom of trees so that the water runs past, he says.
Soil type is another factor. “Clay soils hold water and puddle more easily than sandy soils,” he says. Adding organic matter and gypsum can improve the drainage of clay soils or mud created by heavy rains. But because nutrients leach out of well-draining soils they always need feeding.
To help prevent mould, maximise airflow by maintaining space between plants and keep grass beneath trees minimal, he advises. Also remove decaying or diseased foliage. Temporarily covering plants (with a polytunnel for example) is potentially useful but may increase the risk of mould.
Focus on plants that can manage wet conditions. “Most fruit and nut trees don’t need a lot of sun,” Lillington says. “They will keep on ripening anyway because trees respond to heat as well as sun.”
Sansom recommends creating a rain garden and storing the water in your soil. Rushes such as the knobby club rush are great for bordering these and are able to handle periods of rain inundation plus dry conditions, he says. Lemongrass, Vietnamese mint and Vietnamese basil also thrive in waterlogged gardens and hail from subtropical areas that get a lot of rain. Chilli and capsicum can also tolerate a bit more wet, he says.
Timing is another strategy. Avoid growing moisture-sensitive plants over a rainy spell, Sansom says. And choose fast-turnover foods like leafy greens, spinach, basil and other picking crops. “Grow a crop of cherry tomatoes rather than big Beefsteaks that take ages to ripen,” he suggests.
Extreme wind
Strong winds, especially very hot or cold ones, can be especially damaging to plants. Wind can break, freeze, burn or kill plants, Lillington says. The hottest winds come from the centre of the continent. “So if you’re in Sydney, the hottest wind is the west wind coming from Alice Springs direction,” he says. “For those in Melbourne, it’s from the northwest, and in Perth, a northeasterly blowing down from the desert.” Cold winds, because they’re coming from Antarctica, are almost always from between the southeast to the southwest, he says.
Regardless, the solution is a windbreak. “Sometimes a fence is enough, but it’s better for the environment to grow your windbreak,” Lillington says. This should be a mix of hardy, evergreen species with fast-growing trees like wattles and slower growing trees. In urban situations, fencing and hedging is more common. “A hedge takes a few years to grow, whereas a fence can be put up immediately,” he says. Gates and driveways may act as a wind funnel into your garden.
A windbreak should ideally be five times the height of what you’re aiming to protect. “There’s a one to five ratio,” Lillington explains. “If a windbreak is two metres high, you’ll feel the benefit for up to 10 metres behind it. So you don’t need a very high windbreak to protect quite a lot of garden; a two or three metre high windbreak will protect a standard suburban garden.”
Windbreaks are particularly crucial for coastal gardens, which tend to be buffeted by strong coastal winds and salt, he says.
Sansom recommends shaping a windbreak hedge from bay, feijoa and carob (the last requires a male and female plant to produce fruit). Rosemary can be shaped as a shorter hedge up to a metre and a half. Wind- and heat-tolerant ground covers, like prostrate rosemary, blue chalk sticks and baby sunrose, are also helpful, he says.
Extreme cold
While our world is warming, a large part of continental Australia away from the coast still suffers from frost, Lillington says. Frost occurs when there is a clear sky and the heat of the earth can radiate freely into the sky, he explains. The second factor is altitude. “The higher up you are, the colder it gets. And, generally, as you move towards the centre of the continent you’re going uphill,” he says. “Pretty much any inland Australian town can get frost until you get to the tropics.”
Latitude and season influence the length of the frost season. “Further north, your frost season is not as long,” he says. “Frost happens most widely when the nights are longest, June to August. In some places where you’re well away from the sea and up high, frost can go into November.”
When temperatures drop to around zero degrees, the water in plant cells freezes into ice and expands, he explains. “Certain plants are called frost-tender because they can’t survive that.”
Strategies to keep plants alive include planting cold-tender species (like citrus) in pots and moving them into greenhouses over winter, Lillington says. An alternative is frost cloth over the foliage, roots and soil when frost is forecast. “That’s like putting a blanket on the plant,” he says. “The soil has a mass and loses heat more slowly than the air. It is like a brick sitting in the sunshine, absorbing and retaining heat. When you put a blanket over the tree, during the night the heat is still radiating up from below.”
In locations where temperatures drop below minus two, such as Canberra, the Snowy Mountains, Victorian Alps and New Zealand’s South Island, he advises avoiding growing plants associated with more tropical environments. Growers in frost-prone regions commonly use greenhouses or polytunnels — polythene-covered structures which allow sunlight and heat through, he says.
On the upside, there are many plants that thrive in cold, including garlic, peas, broad beans, and the brassica (cabbage) family, he says. “Winter is actually a good time for growing some things.”
Sansom says, “Anything deciduous or perennial, where it dies back to the ground or loses its leaves, will take anything Australia can dish out in in terms of extreme cold. So apples, pears, cherries, stone fruit — there is nowhere in Australia too cold for those plants.”
Evergreen strategies
Ideally, Lillington advises those aspiring to a highly productive garden avoid living in an extreme climate. If moving to greener pastures is not optional, he suggests growing plants best adapted to the extremes of your area and tapping into local knowledge by joining a gardening club or permaculture group.
Focus on perennials over annuals. “Perennial plants are better than annuals in any extremes — that is why nature always moves towards them,” he says.
Plan for two distinct sets of gardens annually, such as a rainy season and dry season garden or a cold and hot zone garden. “In a lot of areas, you have to have a distinct summer and winter garden,” he says.
Sansom recommends growing a diversity of crops. If one crop fails, you’ve still got something else.
Also, influence genetic breeding by saving seed from individual plants that thrive best. “If you grow a crop of Tigerella tomatoes and one is noticeably better, save the seed off that one,” he suggests. This only works with open-pollinated varieties (not F1 hybrids, plants bred using two vastly different parents that are therefore not reliable in the next generation).
While gardening remains challenging, it is an opportunity to reduce the original problem — greenhouse gases — through urban vegetation, he concludes.
