Managing lawns in hot weather

With a wetter and cooler-than-average warm season so far in 2022 and 2023, we haven't had a lot of heat to deal with but with hot conditions landing on us this week, there are some key things that you can do to protect your lawn from the searing heat.

While this heatwave will be short-lived, there will be no doubt more to come and being prepared is key to success when managing your lawns in hot weather. 

In South Australia, most people either have a couch, a kikuyu or a buffalo lawn. These types of lawns are called Warm Season Grasses and, as the name suggests, are right at home in the warm temperatures we receive during summer. Even heat wave conditions can't kill these lawns! What will phase them in hot, dry weather is a poor level of soil moisture. The simple fact is that poor soil moisture leads to browning off during hot conditions, and while that may seem like common sense, it can be quite a task to get enough water deep down into the soil where it's needed.  

If you're anything like me, and you don't want to see your lawn get fried as the temperatures creep towards the 40s, you'll no doubt give your lawn a good drink before the hot weather hits. The problem we see a lot of in regard to this is that poor watering practices and poor soils often mean that not enough water makes it to the root zone of the lawn where it is most needed.  Let me explain.

When it comes to soil:

• Most soils don't wet evenly. This will mean that some areas of your lawn will absorb more water than others. The patches that don't absorb as much will be the first to dry out when the weather heats up.
• Some soils don't absorb water at all. This is where they are water repellant which is far more common than you might think. Even after watering, the water does not penetrate very far into the soil. The rest either runs off or evaporates. This is a dangerous condition to have in your lawn because if you aren't aware of it, you'll think you've watered your lawn when in fact, you haven't! - well, not enough anyway.  

When it comes to watering:

• Some irrigation systems are inefficient. Sometimes sprinklers are broken, or some areas of the system deliver more water than others. Sometimes sprinklers are blocked by overgrown plants.
• Some irrigation systems take longer to deliver water than you think. New generation sprinklers like Hunter MP rotators or Rainbird RVANS only deliver water at the rate of 10mm per square metre per hour. To give your lawn a good drink (20mm), you'd need to leave them on for 2 hours. In comparison, a traditional spray pop-up will spray out 20mm of water in as little as 20 minutes. Knowing your sprinklers helps you to know how long to leave them on.

To be clear, the goal of protecting your lawn against the adverse effects of heatwave conditions is to ensure there is enough moisture around the root zone of the lawn.  The lawn's roots will draw on the water in the soil, and it will be business as usual. If any of the conditions above exist, then you won't have achieved this across your whole lawn, even if you think you have. In the case of water-repellent soils, all of your lawn will be dry and susceptible, even if you've watered it.

The biggest tip I can give you here is – don’t assume your soil is well watered just because you watered your lawn. It’s a logical assumption but, nonetheless, one that can lead to trouble.

To test how effectively you are watering and how well your soil absorbs moisture,  water your lawn as you usually would. Once watered, get a trowel and dig a small inspection hole. Do this in several places around your lawn and check if the water got down to 50mm. Pay particular attention to patchy areas.  You may be surprised to discover that the water you applied only wet the surface, which is a real issue when high temperatures quickly dry the soil out. Depending on what you discover, more water may be required until a deep soak can be achieved. 

I strongly recommend regular applications of a liquid wetting agent such as Paul Munns Betta Wet, which is best applied in the cool part of the morning. Liquid wetting truly is the tonic of life for lawns during summer - it's one of the most important things you can do for your lawn. Wetting agent ensures that the water you apply penetrates evenly and deeply into the soil. It's best to apply 2 or 3 times over the summer so that all of the water that hits the soil either from you or from the sky is utilised to its fullest potential. 

Once you have ensured your soil wets evenly, you'll be surprised at how well your lawn responds. It will grow deeper roots (because there is water deeper in the soil), which leads to better lawn health and better drought tolerance. In time, your lawn will need to be watered less frequently, even when temperatures get hot.  

Tips for surviving heat wave conditions - Before or during the heatwave:

1. Check your irrigation system and ensure that it is working efficiently and isn't being blocked by overgrown plants and trees. 
2. Ensure all of the lawn is being watered evenly.
3. Apply a liquid wetting agent during the cool part of the morning. 
4. Water the wetting agent in with around 25mm of water. This can take anywhere between 20 minutes and 2 hours per zone, depending on your irrigation system. If you want to test this, try using some catch cups. Placed around your lawn, these cups measure how much water is being applied in mm. Turn your sprinklers on for an hour and see how much water in mm you collected.

As I said earlier, the key to your lawn pulling through a heatwave is all about managing soil moisture. Get this right, and your warm-season lawn will thank you for it.