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Why is my grass turning yellow – and how do I fix it? Top gardening experts explain

Dog lying on yellow grass with blue toy
(Image credit: Alamy)

A healthy green lawn is as desirable a garden feature as a flowerbed in full bloom or an outdoor kitchen. So if your grass is turning yellow, you'll probably want to do something about it.

The yellowing of a lawn is a sign that the grass is deficient in chlorophyll. It's to be expected over long spells of hot weather, which is a sign that it most likely needs water. 

However, there may be other reasons why your grass changes color, and this is when it's wise to administer some good green lawn care (opens in new tab) fast. That's because if your grass then turns from yellow to silvery blue, then we're afraid it's dead, and there's no hope of recovering it. 

Why is my grass turning yellow?

1. You're cutting the grass too short

Giving your grass a regular 'haircut' is a great idea, right? After all, no one wants an overgrown jungle of a backyard. But going too short could be causing more harm than good. Both Monty Don and Martha Stewart warn against going too short. The best height to cut grass (opens in new tab) is between two and three inches high. But if it does grow quickly, don't be tempted to lop masses off the top to achieve this level.

"As a rule of thumb, we cut no more than a third of the grass blades at a time," Martha told The City Life (opens in new tab). "Because if we cut too much, it will damage the grass and cause browning and grass loss. Plus, grass that is cut properly thrives in a wider range of weather conditions."

So when it comes to the first cut of the year, take it easy. "The grass will need mowing in March but do not cut it too short," Monty Don explains on his MontyDon.com blog. "Just give it a light trim for the rest of this month and the grass will be a lot healthier – and better able to resist summer drought – as a result."

If a drought is forecast, be super cautious. Martine Le Gassick is a gardening expert & creative director at garden design company Stark & Greensmith (opens in new tab). She says, 'try to not to cut your grass too short before a drought. Leaving the grass taller also helps to retain more moisture in the soil. Try to keep your grass 6 inches.'

Our picks of best gas lawn mowers (opens in new tab) and best electric lawn mowers (opens in new tab) make it easy to set what level you cut your grass at, so there's no danger of hacking it too short. 

2. You're watering your lawn the wrong way 

What the expert says...

Kate Turner is an award-winning garden designer and Miracle-Gro (opens in new tab) 'Gardening Guru'. "Did you know your grass can be stressed? Hot weather combined with lack of water sucks all of the moisture from your grass, causing the blades to have a straw-like texture. Poor watering can cause your lawn to have shallow roots, meaning it can’t access the water deep within its soil. But don’t panic, be patient! More often than not your grass will recover as soon as it rains. If you feel you must water, make sure you do so early in the morning with a sprinkler. Avoid mowing and feeding the lawn when it's yellow, as this will only stress the grass further."

It's tempting, particularly through a long stretch of dry weather, to keep watering the grass. But a little-and-often approach might not be the best thing for your lawn. 

Chris Bonnett is a trained horticulturist and supplies plants to show gardens and celebrities. "Instead of watering your grass everyday for short periods of time, try and give your grass a longer and deeper water a few times a week in order to penetrate right down to the roots," he advises. "Leaving it for a couple of days will give the grass plenty of time to soak it up before the next watering."

You should also aim to water your grass early in the mornings or at dusk, when it’s cooler outside.

3. Dogs are using your lawn as a bathroom

"Many of us share our home and garden with a four-legged friend. But dog urine, particularly from female pooches, can cause a lawn to look scorched and yellow," says Paul Hicks, marketing manager and lawn care expert at STIHL (opens in new tab).

This is caused by the nitrogen it contains. A little nitrogen is actually good for a lawn – for example, in a fertilizer. But in higher quantities, it will cause yellowing.

"You can usually tell your dog is the problem if you see round patched of scorched grass with taller bright green shoots on the perimeter," Paul explains. 

"To stop this from happening, maintain moisture levels in your lawn to dilute any dog urine and reduce any potential damage. Pour lots of water on the grass immediately if you see your dog urinating."

4. You haven't aerated your lawn

"The best grass likes very well drained soil," says garden expert Monty Don, and we're inclined to agree. By aerating – or making lots of very small holes – in your lawn, you're helping your grass roots to gain access to all the air, water and nutrients they need. You don't need to do it often. Once or twice a year should be fine.

The job can be done manually. Monty's preferred way to aerate a lawn (opens in new tab) is "sticking a fork in the ground and wiggling it about and repeating the process every 6 inches or so". However, if you've got a larger area of lawn to work on, you may want to take Martha Stewart's advice.

"Aerating a lawn can be done manually with a variety of tools, but depending on the size of the yard, it can become quite time-consuming," Martha explains on her blog, Martha, Up Close & Personal (opens in new tab). "Gas-powered aerators reduce the time it takes to do this job. We used a Ryan walk-behind core aerator. It worked really well to cover the large area of grass."

Martha chooses early Fall to aerate her lawn, but early Spring is a good time, too. 

5. You haven't fertilized your lawn

Yep, it's not just our flowerbeds that need to be fertilized. A lawn will benefit from a few treatments of fertilizer each year, in early Spring, late Spring and in the Fall, before it gets too cold. 

"Apply the fertilizer when the soil is moist, and for a really lush lawn, keep feeding it into the summer months," says Paul Hicks. "You should stop in the height of summer, though."

Another lawn fertilization tip (opens in new tab) is to spread your fertilizer evenly. Wet it, then leave it settle for a few days before you water it again. 

What else can I do to help my lawn turn from yellow to green?

What the expert says

"Keep a yellow lawn at bay by leaving your grass clippings on your grass after mowing it. You can do this with a mulching lawn mower (opens in new tab), which will automatically return the fine cuttings to the lawn," says STIHL's Paul Hicks. "But avoid mulching when it’s wet – damp clippings can build up under the mower and won’t break down on the lawn. The idea behind this is that the clippings will decompose and return nutrients to the soil, encouraging healthy new growth. You'll see a difference within a few months, with the added bonus of not having to get rid of your grass cuttings."

Another way to prevent a lawn from turning yellow is to apply what's known as a 'top dressing' a couple of weeks after you've applied your fertilizer. This will encourage your grass to grow thick and strong by providing it with extra nutrients. 

A top dressing typically consists of a mix of sand, soil loam and peat. Although peat free advocate Monty Don recommends: "equal portions of sieved topsoil, sharp sand and sieved leaf mould or compost". 

"If you do not have these things to hand then just sharp or silver sand will do the job," Monty explains. "Spread it across the area you have pricked and brush it in with a stiff broom, filling the holes with the mixture. This will help drainage and feed the grass."

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Amy Cutmore

Amy Cutmore is Editor-in-Chief, Homes Audience, working across the Future Homes portfolio. She works on titles including Ideal Home, Homes & Gardens, Livingetc, Real Homes, Gardeningetc, Top Ten Reviews and Country Life. And she's a winner of the PPA's Digital Content Leader of the Year. A homes journalist for two decades, she has a strong background in technology and appliances, travelling the world in pursuit of the biggest TV screens, the smartest phones and – oh yes – the most efficient washing machines.