By Rob Sproule
When a heat wave hits, it’s not just humans and pets who get uncomfortable. Prolonged high temperatures bring a lot of stress to gardens, but there are easy things that you can do (and avoid doing) to help your plants beat the heat.
“If you saw a heat wave, would you wave back?”
– Steven Wright
When to Water, and When Not To:
Try to water first thing in the morning. It can seem like a chore, but a walk around the garden before heading to work can really clear the head. An early soaking will keep the soil cool as the mercury rises and give the roots a cushion of moisture into early afternoon.
If mornings aren’t an option for you, the next best time to water is in the evening, after the scorch has soothed. However, if the nights are cool, mildew may set in.
Avoid overhead watering in the afternoon heat. It’s a pet peeve of mine to see water being launched high into the air by sprinklers at 4:00 pm on a hot day. Not only is it highly wasteful—most of the water just ends up evaporating before it has a chance to soak into the ground—but it’s expensive, as well. If you must water during the day’s heat, invest in a soaker hose that keeps the water on the ground.
Keeping Roots Cool:
Plants have different types of root systems depending on where they come from. Native or other cool-climate plants tend to have deeper roots and are therefore better equipped to handle dry conditions. Tropical plants, such as tomatoes, peppers and many annuals, have roots close to the surface. Try to give them a little extra water; otherwise, when the soil dries and hardens, it could damage the roots.
Dark soil absorbs heat like a sponge, and hot soil can be dangerous to the roots just under the surface. Keep the soil cool by adding mulch around heat-sensitive plants such as salad greens, root crops and pansies. Cedar mulch or straw is best; avoid rock because it will heat up and actually make the problem worse.
Minimizing Heat Stress:
Keep your lawn a little longer in the heat. Longer grass blades (around 7.5 cm) will help keep the roots cool by shading the soil, and more leafy tissue means more ability to transpire, which helps cool the plant.
Just like you don’t want to go do push-ups all day in 30°C heat, your plants don’t want to work hard in the heat, either. Avoid “surgical” tasks such as transplanting until the weather cools off a little. Root systems work overtime in heat and don’t need any extra disturbances.