In Perth, our summers aren’t just hot; they are long and bone-dry! Too often we’ll have a scorching hot day in Summer, and when you walk out into the garden at 4pm everything is looking a little sad and wilted. Here is how to keep your garden thriving when the mercury hits 40°C.
Know your watering days.
- Most of us are on a two day-per-week watering schedule. Check the Water Corporation website to ensure you’re on the right days for you house number.
- Never use your sprinklers between 9am and 6pm. The evaporation rate is so high that you’re essentially paying to water the air!
Deep Soaks vs. Light Sprinkles
The biggest mistake gardeners make is watering for 5 minutes every day. This encourages “lazy” roots that stay near the surface where the soil is hottest. On your rostered days, give your garden a deep, long soak. The goal for a true deep soak in our sandy soil is to get water to penetrate 20–30cm deep (the primary root zone). This encourages roots to grow deep into the cooler subsoil, making the plant much more resilient to heatwaves.
- If you’ve got sprinklers, that is about 15-20 minutes.
- If you’re hand watering, that about 2 to 5 minutes per square metre. If you see water pooling or running off, stop, wait a minute for it to sink in, and then continue.
- If you have delicate plants in hanging baskets or small pots: On a 40°C day, place a few large ice cubes on the surface of the soil (away from the stem). As they melt, they provide a slow, cold drip-feed that keeps the root ball cool without shocking the plant with a flood of hot water from a hose that’s been sitting in the sun.
Don’t Let Your Soil “Reject” Water
Perth’s sandy soil is notorious for becoming hydrophobic (water-repellent). If you see water pooling on top of the soil or running off into the driveway, your plants are likely actually thirsty underneath.
If you think this is happening to you, apply a high-quality wetting agent. It acts like a detergent for your soil, breaking the surface tension and allowing water to reach the root zone.
Give Your Plants “Sunscreen”
We wouldn’t go outside without our SPF and hat, and your soil shouldn’t either.
- A 5–10cm layer of coarse mulch can reduce soil temperature by up to 10°C. It’s the difference between your plants’ roots “boiling” or staying cool.
- For your delicate plants, don’t be afraid to use temporary shade cloth on 40°C+ days. Even an old bedsheet or a beach umbrella can save a plant from permanent leaf scorch.
The “Secret Sauce”: Seaweed Tonic
If a heatwave is forecast, give your garden a dose of liquid seaweed (like Seasol) the night before. It’s not a fertilizer; it’s a plant conditioner that strengthens cell walls, helping plants cope with the “stress” of extreme heat.