Does watering grass in the sun burn it?

When tending to your garden this summer, the question of does watering grass in the sun burn it might cross your mind. 

Perhaps you've had this thought because you noticed your lawn turning brown despite a rigorous watering routine with hosepipes and the best water butts or perhaps you just heard someone mention it.

But is there any truth to the claim? We spoke to David Hedges-Gower, chairman of the Lawn Association, to find out if watering grass in the sun can burn it.

Before he answered, he was keen to first point out: "What works for one lawn will not always work for the next.  Different location, different lawn, different species and most of all a different idea on what they want from their lawn."

Does watering grass in the sun burn it?

Essentially, watering your lawn when the sun is hot and shining directly on it can cause damage. Blades of grass will normally shut down in the heat, only growing when the cooler part of the day descends, Hedges-Gower explains. This is because the stomata closes, which is particularly true of native British grasses. 

"Watering is always best done at night, one when the plant can grow and two, when it can take it and not evaporate," says David. "But you need to start early with watering, before it goes brown and dry, as it will take a lot more water to lift it back to a green carpet again."

Alastair Culham, associate professor of botany at the University of Reading, agrees saying that grass can be damaged if watering in full sun. However, he adds that: "The notion that wet leaves on sunny days cause scorch in plants was disproved nearly ten years ago but there is no doubt that watering in full sun is not water efficient – as much of it will evaporate before entering the soil."

David Hedges-Gower points out that mowing your grass too short can make your lawn more susceptible to damage when hot weather arrives. "why water when you mow at 30mm?" he points out.

But the key to keeping your grass looking healthy over the summer is all about your soil quality rather than watering. "Watering will cause harm to soils. And you may be adding to that with the decision to irrigate when it does go dry," warns David. 

"Firstly decide to enhance your soil's water storing space as compacted lawns (caused by water) will not even make use of the water you are applying. Most will run off and not be of any use at all."

The exception to this is with newly-laid turf, which will require constant watering through-out the summer months, but obviously not during the heat of the day.

Should you water grass at night instead?

Watering the lawn at night is a great idea where possible, says Hedges-Gower when talking about the best time to water grass. 

"10pm can be a good time as this is when the plants (grasses) can make use of the water and it will be cool enough not to evaporate," he explains.

There is some debate from golf course enthusiasts that watering at night can cause diseases to flourish in your grass but this is only really a factor if you keep your grass very short for game play, he says.

How long should you spend watering a lawn?

The question as to how long to spend watering a lawn during the summer months isn't an easy one to give generic advice on, David Hedges-Gower says. But watering so that it soaks further than 4 inches below the surface is when it starts to redundant as the grass cannot suck it up that deep.

"Water is precious and best use has to made of what we apply and you should start with low water times and build yourself up to the level you are happy with, "Hedges-Gower explains. "Decide if you need to water at all as native grasses will come back after a dry period."

What is a good idea is to make your soil healthy so it can hold more water when it is hot and drain well when it is wet.

David Hedges-Gower

David is one of the UK's leading lawn experts, with over 30 years' experience in the industry. He is Chairman of the Lawn Association, an educational platform for homeowners and professionals, and founded the world's first lawn care qualification.