As any pro gardener will tell you, caring for a lawn properly is an exact science, and even when it comes to something as simple as watering, nothing should be left to chance.
A big part of this has to do with timing, and to help you get it right, here’s our detailed guide to the best time to water grass to ensure you achieve the results you desire.
If you’re looking for a preview of some of the stuff we’re going to be talking about, you can also watch this video before reading on.
The simple answer – when is the best time to water grass?
For anyone who wants to know the best time of day to water grass, let’s start with a simple answer. After that, we can dive a bit deeper into the theory of when to water a lawn and the best way to do it to ensure superior results.
So, when is the best time to water a lawn?
The answer is, first thing in the morning, ideally before around 10am.
This is because at this time, the weather is cooler, so there will be less evaporation. If you water the water when the sun is at its most powerful, more of the water will evaporate off and less will penetrate the ground, so earlier in the morning is preferable.
At this time, there is also less likely to be a strong wind, which can similarly increase the rate of evaporation.
If you can’t water first thing in the morning, the second-best time is in the afternoon, around 4-6pm – and for the same reasons.
At this time, the hottest part of the day has already passed, so less of the water will evaporate and more will be able to soak into the ground, reaching the roots of your grass.
At the same time, the surface of your lawn will have more time to dry before nightfall, making your lawn less susceptible to pests and disease that thrive in cool, damp conditions.
When is the worst time to water a lawn?
Just as there is a best time to water a lawn, there is also a worst time – and that time is in the evening, just before nightfall.
As we just alluded, when grass remains damp overnight, it is more vulnerable to being attacked by disease, so you need to give the surface of your lawn enough time to dry out before the sun goes down.
In fact, some professionals claim that watering you grass late in the evening is one of the worst things you can do, along with cutting it too short when you mow it.
How to tell if your grass needs watering
Grass doesn’t need watering all year round, and this is something we’ll come back to in a moment. However, there are times when your lawn does need a little help, so how can you tell if your lawn needs watering?
The easiest way to tell is just by looking at it. If it looks green and healthy and there are no yellow areas where it appears to be drying out, the chances are you don’t need to change what you are doing.
However, if it begins to lose its lushness and starts to turn grey, yellow or brown, this could be a good indication that your lawn is getting thirsty.
One simple test you can do is just to walk on it. If the footsteps remain in the grass and it doesn’t spring back immediately, this can indicate that it is lacking the moisture it needs to stand up again after being walked on.
Another test you can do is to push a screwdriver into the soil. If you find it hard to push the screwdriver to a depth of around 15cm (6”), this can also tell you that the ground is hard and dry and in need of watering.
What is the theory behind watering a lawn?
Not everyone might realise, but watering a lawn properly is slightly more complicated than turning on the sprinkler from time to time when you think your grass might need a drink, so now let’s look in more detail at the theory.
A healthy lawn needs around 2.5cm (1”) of water per week, either from nature or from you.
However, the way this water is delivered is important.
If you water your lawn a little bit every day, the grass won’t have any incentive to send down deep roots since water will always be available near the surface.
This will mean your lawns looks superficially healthy, but as soon as it faces a time of stress – for example, if there is a drought – its shallow root system will not be able to withstand the tougher conditions and your grass will die.
For this reason, it is much better to deliver the 2.5cm of water your lawn needs in the form of less frequent, deeper soaks, perhaps two or three times a week.
Each time, the water should penetrate the ground to a depth of around 15cm, where it will remain accessible for your grass’s roots.
This way, you will encourage your lawn to send down deeper roots, making the grass hardier and better able to withstand more difficult conditions.
Here’s a video that discusses these and other related considerations.
How can you judge how much water to give?
As you should now realise, watering a lawn is about much more than just guesswork, and the more scientific you can be about it, the more successful you will be.
This means the next step is working out how long to water your lawn each time, and fortunately, this is easy to do.
Assuming you are watering your lawn with a sprinkler, you need to work out how long it takes for the sprinkler to deliver 2.5cm of water.
The best way to do this is to set the sprinkler up in the garden and place a few coffee cups or bowls out on the lawn. All you then need to do is time how long it takes for each one to fill up with 2.5cm of water.
(Pro tip: if you don’t want to waste water doing this or risk over-watering your lawn, time how long it takes for 1.25cm of water to collect in the cups and then double it for 2.5cm.)
Then, for example, if you find it takes an hour for your sprinkler to deliver 2.5cm of water, you can then water your lawn three times a week for 20 minutes or twice a week for 30 minutes each time.
Do you always need to water a lawn?
We all know how notoriously rainy the UK’s weather can be, and there is a good chance you won’t always need to water your lawn, even in summer – if the good old British rain is taking care of things, obviously you won’t need to do it yourself.
On the other hand, recent years have also brought more than the occasional summer drought, and if you want to keep your lawn lush and green, you will need to water it during periods of reduced rainfall.
However, during the most extreme conditions, some areas can be hit by hosepipe bans, so what then?
In that case, it is usually ok to simply leave your lawn unwatered. When this happens, your lawn will go yellow and may seem to die. However, it isn’t dying but rather is just going dormant, and once the rain begins to fall again, it will spring back into life.
The only thing to avoid is inconsistency. If your lawn goes dormant, leave it. If you water it a bit and then leave it to go dormant for a bit and then water it again, you will put it under too much stress.
So water it or don’t water it – but don’t go half-and-half since this is the worst thing you can do.
What about new lawn?
If you have recently sown grass seed, the guidelines are a little different. New seed needs to be kept moist – but not wet – for the first 10 days or two weeks to allow it to germinate.
This means that light watering every day is preferable – and indeed necessary – if there is no rainfall.
After the seed has all sprouted, you can then revert to a normal watering pattern as described above.
Watering hard soil
If your soil has become hard through drought or compaction, you will need to soften it up gradually – because if you just dump the water on top, it will sit there until it evaporates off, and it won’t penetrate to the roots where you need it.
In this situation, water in shorter bursts, for example watering for 10 minutes, leaving it to soak in and then returning for another 10-minute session.
Once the ground begins to soften up, you can also help matters by aerating the ground, either using a standard garden fork, a pair of aerating shoes or a machine. This treatment will also help the water to penetrate the soil, where it will be of maximum benefit to your grass.
Understand the theory – and the rest is easy
When it comes to watering lawns, as long as you understand the theory behind what you are doing, the rest is easy. Make sure you give your grass enough water while encouraging it to send down deep roots, and the appearance and health of your lawn will benefit immensely.