How much water does a lawn need?

On Saturday, 23/3/24, during the ABC Talk Back Gardening Show, Jon asked me, “How much water does a lawn need? Particularly, how long do you need to water and how often?” It was a particularly relevant question given the recent heatwave in Adelaide.

In 2007, IPOS Consulting was engaged by the SA State Government to develop the Irrigated Public Open Space Code of Practice. The Code was developed to effectively manage water resources while ensuring that South Australia’s public, irrigated turf spaces were maintained so that they were fit for their intended purpose. Essentially speaking, it forms the basis by which turf managers can demonstrate efficient, effective water resource management. While it was written for professional turf managers in the public space, many of the principles contained in it can be applied to how you might go about managing residential lawns. It is well worth reading if you want some research and data-driven insight into answering the above questions. I have mentioned this because, later in this blog, I will reference this Code in some of my recommendations.

In considering the above questions, and before answering them (which I promise to do!) it is important to go over a few other things first.

What is the intended purpose of the lawn, and what do you want it to look like?

If you have a lawn, you will have a purpose for it. This may be something you’ve never articulated, but I guarantee you’ll have one – and it’s worth understanding what it is because it will help you to answer water-related questions rather than simply taking the advice of someone else who doesn’t understand your unique circumstances. There are many reasons why people want to own and maintain a lawn. Some want it as a feature to make their home look good while not intending to use it much. Others want it as a recreation space for their family or as a place for their pets to toilet. Different uses require different demands from the lawn and will affect how much water is required to maintain it. The higher your use expectations are, the faster the lawn will need to grow to keep up, leading to a higher water requirement. Visa versa, the lower your use expectations, the less water your lawn will need.

Some people don’t mind if their lawns brown off and become a bit patchy during the dry Summer months. Others want it to look pristine and dark green all year round. This, too, will affect how much water your lawn will need to meet your expectations within your water budget. In most cases, maintaining a higher-quality surface will naturally require more water. 

It’s important to note that the above considerations are neither right nor wrong. They are simply things to consider when determining how much water your lawn will need to meet your expectations. Not considering these things would be amiss, as you would not have spent enough time thinking through your circumstances to come to an answer that is right for you. This will become clearer as you read on.

Considering climate and rainfall

While it may seem obvious when we talk about how much water and how often, any conversation like this will naturally focus on the warmer seasons of the year when watering will most likely be required. Even in the context of the warm seasons, when a lawn is most likely to suffer from moisture stress, there is a lot of variability, and when you combine that with climate change, the thought of being able to program your irrigation at the start of Spring and not touch it or change it until mid-Autumn isn’t reasonable. It’s a moving feast, and that’s the problem with black-and-white questions such as how much to water and how often because, in reality, the answer is always, “It depends!”. Did it rain? How much did it rain? Was it hot? How hot? Was there a heat wave? These factors affect soil moisture and vary how much you need to water your lawn. Better questions would be, “What moisture level should you maintain in your soil and at what depth? But I understand that’s hard to get a handle on and probably reserved for the biggest of lawn geeks.

What type of lawn do you have?

The lawn type you have greatly impacts how much water you need to apply to maintain your expectations. Warm-season grasses such as couch and kikuyu use up to 50% less water than cool-season grasses such as rye and tall fescue. Most people in South Australia have either a couch or kikuyu lawn, so this article was written primarily with these grasses in mind. If you have other varieties, please seek further advice before acting on the recommendations of this blog.

Considering the soil under your lawn

The type of soil under your lawn will impact how often you need to water and for how long. The sandier the soil, the lower its water-holding capacity. While this may seem at odds with the general recommendation to use sandy loam soils when installing a lawn, it is also true that open soils, such as sands, allow for a much deeper root zone than heavier soils, giving the lawn access to water deeper in the soil profile which is ideal for lawns.

On the negative side, sandy soils can tend to repel water. This is common in Adelaide and needs to be dealt with when managing water consumption in lawns.   I’ve written a lot about this on my blog, and I can’t say this clearly enough – if your soil is non-wetting, it doesn’t matter how much you water or how often – your lawn will still suffer from moisture stress during warm weather because water won’t be able to penetrate through to the root zone where it’s needed. Non-wetting soils must be regularly treated with liquid wetting agents to prevent water wastage and moisture stress in lawns.

When watering, you ideally want water to penetrate at least 50mm below the surface. The only way you will be able to know this is to perform some investigative work after you’ve watered – at least at first, when you’re getting to know your lawn. Armed with a hand trowel, dig into your lawn after watering to visually inspect the moisture level. Alternatively, buy a soil moisture probe. In this way you’ll begin to learn the unique characteristics of your soil and how to manage your watering program in context with it.

What about the dynamics of the area your lawn exists in?

Factors like shade will affect evaporation rates. The land’s slope will affect run-off rates, and radiant heat from a fence can dry an area out faster. While these factors have less impact, they still need to be considered.

How will it be watered?

How you water your lawn will affect how much water you use. Pop-up sprinklers are more effective than movable hose-end sprinklers or watering by hand, but they must be in good working order, and the system must be designed properly. Correct sprinkler design considers water flow, water pressure and the unique shape of your area. When done properly, the system will water your area with a high level of efficiency. It’s also worth noting that some sprinklers are more efficient than others. To utilise the best technology in residential pop-up sprinklers, use a mini-rotator style sprinkler such as Rainbird R-Van’s or Huner MP Rotator’s. They can be retrofitted into most existing systems and will dramatically reduce the amount of water you use compared to traditional pop-ups.

To summarise so far…

Considering the purpose of your lawn, how you want it to look, what type of lawn you have, the soil type present under your lawn how it will be watered will help get a grasp on deciding how much to water and how often. By understanding these things, you have a much better chance of realising significant water savings while maintaining the expectations you have for your lawn.

Now that you have some background, what I am about to say will make a lot more sense. I understand if you’re feeling like it’s all a bit too complicated, and while it can be, it doesn’t have to be. You can make some generalisations to develop a strategy that can simplify your watering, reduce waste and give you the lawn you want.

Back to the questions: How much do you water, and how often?

Since this is something we get asked so often, a little while ago, we had a chat with IPOS Consulting, who developed a digital tool to help us answer these questions more accurately. It gives us real-time water use data, sprinkler run times, frequency of watering and even the estimated water cost over a year for a customer’s lawn, all presented in an easy-to-follow chart. This is great at answering the above questions with a high amount of detail and something we’re more than happy to do for our customers. For the sake of this blog, I’ll give some more general advice that is still very helpful.

By now, you will have guessed the frequency of how often you water your lawn and how long for can be understood both in considering your unique circumstances and, more broadly, your expectations for the lawn, and this is where we turn to next.  

Categorising your lawn

In the IPOS code of practice, they do this by classifying the intended function of the lawn into categories. Different categories require different amounts of water to deliver the required outcome for the lawn. For residential lawns, I think we can capture most people’s expectations of their lawns into three categories: Each category includes benchmark water usage per annum in litres and kilo litres and is for couch and kikuyu lawns.

Category 1: Elite Lawns

Maintaining a lawn to the highest standard, expecting green, uniform looks all year round, with the capacity to tolerate high wear.

• Highest possible quality turf
• Highest visual standard possible – Green all year round, uniform colour
• Highest vigour and turf health
• Capacity to retain an elite standard, even in a heat wave.
• Uniform growth with complete coverage
• For highest-use situations

Approx water required per year (per 100m2)	100,000 litres
Approx water required per week	32 mm
Approx cost per year	$300

 

Category 2: High-quality lawns

This is where most people will sit. It’s where there is a high expectation of year-round colour and performance without the fanaticism that comes with maintaining an elite lawn. Patches may appear from time to time, and the lawn may fluctuate to a degree with seasonal changes

• High turf quality
• Medium to High visual standard
• High vigour and turf health
• May fluctuate in extreme weather conditions
• Turf quality may reduce with winter wear
• Even coverage and density

Approx water required per year (per 100m2)	70,000 litres
Approx water required per week	22 mm
Approx cost per year	$210

 

Category 3: Standard Lawns

This is where lawns are maintained to survive without an excessive amount of water. Aesthetics have less importance with an expectation that the lawn may cycle in appearance and durabilily with the seasons.

• Medium turf quality
• Medium visual quality. Aesthetics have less importance
• Medium vigour and durability
• Turf quality may reduce with winter wear
• Turf may discolour during hot weather
• Turf still maintains even coverage and density
• Passive/minimal use

Approx water required per year (per 100m2)	50,000 litres
Approx water required per week	15 mm
Approx cost per year	$150

 

The above benchmark water recommendations are a guide only and assume that there is appropriate soil under the lawn, an effective irrigation system, the soil isn’t non-wetting, and the lawn is subject to an appropriate fertiliser program. Recommendations are based on average climatic conditions for the Adelaide metro region. Where hotter-than-usual conditions,  wetter-than-usual conditions occur, or site-specific/unique conditions exist, irrigation schedules should be increased or decreased accordingly.

While I’ve given some general water usage data here, how this water data is translated to how often you water and for how long will depend on which category you select, which season we are in (warm months will require a higher frequency and cooler months a lower frequency) and the type of irrigation method you intend to use and is best understood using our digital calculator.

To get started, and at least in the first instance, learn your soil by physically checking how it responds to water. In the watering information above, I've recommended a certain amount of water per week during the warm seasons (eg 22mm per week for the High Quality lawn category).  Use catch cups to understand how long it takes for your watering system to deliver this amount of water. Investigate your soil after watering to get a grasp on moisture penetration, or use a soil moisture probe to test your soil’s moisture level. The best advice I can give you is to know what you want from your lawn and put some time into understanding the unique dynamics of your soil and your lawn area. While this represents an effort at the start, the reward will be a healthier, greener lawn that performs the way you expect it to.

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