Plants to Survive the Heat

Welcome to another week-long heatwave in Adelaide. 

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Is your garden getting tired of this? Are you too tired to be gardening!?

Just a quick bit of observation about what’s doing well and what’s not lately.

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Gleditsia ‘Sunburst’. Pretty tolerant of heat and drought, and their feathery foliage casts sweet dappled shade over surrounding garden areas. Beware though that roots can invade nearby vegetable beds. Canopy is lime green in spring through to green in summer and golden in autumn before leaves drop. Jacarandas are also coping well on local streets.

Garden areas with plenty of shelter, mulch and afternoon shade and adequate water are generally surviving pretty well. I see many pittosporum hedges and young citrus trees suffering, along with trees where the soil is unable to absorb or retain water effectively (especially on steep slopes) or where irrigation has broken down. Some deciduous fruit trees have superficial scorching on outer leaves but will bounce back in spring after a good winter soaking and pruning. But many street trees have been neglected and even established natives are suffering and wilting where they’ve had no water for months. Take pity on them and stretch the hose over the fence occasionally – your own garden will be hotter and more exposed if they die.

Here are some of the great survivors that keep our garden fairly robust and provide protection for their more tender plant neighbours.

Natives

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Templetonia retusa and one of many saltbushes

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Acacia glaucoptera or clay wattle – versatile in full sun or part shade

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Lomandra (mat rush)

All the plants shown above are exposed to full sun all day on a road verge, and have only been watered 2-3 times this summer, when we have had heatwaves forecast. Even if they look a little drab now, they’ll hold on and put on new growth after rain.

Perennial Herbs (hover over images for ID)

These all help to provide shade, windbreaks and/or living mulch to keep the garden cool and to reduce hot winds that increase evaporation and heat stress on plants. They also attract bees and other beneficial insects. All are evergreen except the lemon verbena, which we cut back hard in winter and dry for fragrant pizza oven kindling. All these can survive with minimal to no irrigation depending on their site, but will be more lush and put on more growth if they do get an occasional drink. They are also great in pots.

Fruit trees & vines

Most of our fruits are doing fine, some with more TLC than others, but here are some that are really thriving in the heat. The grapevines have been affected by mildew since we’ve had denser growth and more humidity and yet they keep putting on lush new growth and providing essential shade for our home, veg gardens and chooks.  White shahtoot mulberry is fruiting for the second time this season. Lemons have just kept on fruiting almost constantly (aided by occasional pruning of a branch here and there). Feijoas survive even on the neglected and rarely watered road verge, where they blend in nicely with native plants, but the one that is irrigated in the front garden has fruit swelling for autumn harvest. Our strawberry (red cherry) guavas are also setting fruit for the first time and show no sign of being scorched. These along with feijoas can be used to make a beautiful and delicious fruiting hedge that’s very hardy once established.

Ornamentals

Ornamental plants are never my priority, so they have to be tough to cope with regular neglect here. To minimise my losses, I keep most of them in sheltered locations with filtered light. The potted frangipani has been the outstanding winner for toughness this summer. Last summer I cut the top off and potted it, and it grew well. But the remaining stem seemed to have died, so it was cast aside in my ‘plant graveyard’ (the pile of pots by the shed waiting to be cleaned up and reused). After spending months there without watering or any form of care, this stick suddenly sprouted new leaves and has turned itself back into a fine little tree! Biggest tip for ornamentals – the bigger and lusher their leaves, the more shade they’ll probably appreciate. And watch out for hot sun sneaking into sheltered places as we get closer to autumn and it sails by a bit lower to the north. Those leaves that have been shaded all summer can suddenly get a nasty shock.

What’s suffering?

The answer is really not much, unless it has missed out on watering or has had sudden exposure to direct sun. Young avocados, mango and macadamia have all suffered a bit of sunburn to upper leaves, but will outgrow their sensitivity over a couple more years. Potted herbs and strawberries wilt on a hot day but plump up again with a drink.

What next?

While we are getting enough long heatwaves to feel challenged in the garden, it also feels like a call to action to plant more trees and create more canopy across our city. The more trees we can get established now, before our climate heats up further, the more we will have done to reduce its impacts. Waiting a few more years makes it that much more difficult for young trees to settle in successfully and to do their bit both to absorb carbon out of the atmosphere and to reflect scorching sunlight away from our homes, streets and gardens. When you consider that they can reduce air and surface temperatures by tens of degrees, it’s surely worth devoting a bit of the coming winter and spring to getting trees established in order to benefit over all the future summers.

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