Garden Heatwave: How to Care for Heat-Stressed Plants

Whether you’re coping with a mini heatwave or a summer-long slog of extreme high temperatures, here are a few tips to help you to help your plants cope with heat stress...

Smart Watering

It’s obvious that in hot, dry weather, plants will need more water to keep them healthy and productive. But it’s important to use smart watering techniques to make the most of every drop.

The best time to water is early in the morning, when moisture is slower to evaporate and water levels can be recharged ahead of the heat of the day. Check soil regularly – every day if you can – and water if it’s dry at finger depth. Remember, it’s better to really drench the soil once every few days, rather than merely dampen the surface daily.

Scrape soil into ridges around plants to create bowls to water into, or water into old pots or bottles sunk into the soil next to plants. That way the water will go directly to the roots where it’s needed instead of running away over the soil surface.

Drip irrigation systems set up on a timer are a good option if you’re not able to water daily in hot weather.

Container plants dry out very quickly and may need watering twice a day, especially if it’s windy too. Check that the water is actually being absorbed – you don’t want it just running straight down cracks between the potting soil and container wall. Continue watering until you see water running out of the bottom. You can use pot saucers to hold the water around your pots for longer.

Lock in Soil Moisture

When you’re done watering, it’s time to lock in that valuable moisture. Mulches of organic material such as compost, leaves or grass clippings all help to slow evaporation by shading the soil from the sun’s rays. Mulches also keep the root zone cooler, reducing the stress your plants are under.

You can create a living mulch by planting densely or using rambunctious, sprawling plants like squashes to shade the soil.

Stop Fertilising

When temperatures rise above 85-90ºF (29-32ºC), many plants really start to struggle. Some, like tomatoes, cope by rolling up their leaves – a natural response that reduces water loss. Many fruiting plants, including tomatoes, beans and peppers may also drop their flowers or stop producing new ones as they try to cope with the heat.

Now you may think the answer is to fertilise your crops to make them stronger, but this only exacerbates the situation, because plants will then need even more water to process all that fertiliser. A sudden flush of nutrients also signals to the plant that it’s time to grow – a dangerous and stress-inducing move in soaring temperatures. So stop fertilising and concentrate on watering instead.

Add Some Shade

When it’s hot I love to seek out some shade, and so will many of your crops. Shade plants with anything you can get hold of. Old net curtains works, as do white bed sheets. Purpose-sold shade cloth is available in different levels of sun block, from 15%, 30%, 40% – right up to 100%. Plants won’t grow as fast under it, but they’ll still receive some sunshine and will be a lot less stressed.

Pin the shade cloth into position with bulldog clips or clothespins, using frames or hoops to support it. Many plants will benefit from some shading from hot afternoon sunshine, including cool-season vegetables like cabbage and lettuce, and fruits such as strawberries.

Harvest Promptly

Removing plant material – by harvesting it – means that there’s less foliage or fruits for your plants to have to service. Fruiting and pod-producing plants especially should be harvested promptly to save the plant’s energy. Finish ripening fruits that haven’t fully colored up in the kitchen to give your plants a break. They’ll switch back to their productive selves once the weather cools.

Extreme summer heat can be as stressful for plants as it is for us, but by following these simple strategies you’ll save them a lot of suffering. Now I’m sure you’ve got lots more tips to help your plants keep their cool, so please let us know what techniques you use in the comments section below.