How much water and how often?

“How long do I need to water my lawn, and how often?” These would be two of the most commonly asked questions, and for good reason! Now that the weather is finally warming up, it's a good time to consider these questions in a bit more detail.

 

Factors to Consider Before Lawn Watering

Most people want their lawns to get the right amount of water so that they stay healthy and green, but no one wants to overwater, given the price of water. The answer to the questions of how long to water for and how often is variable and a bit more involved than most people think. Without trying to overcomplicate the issue, there are a few considerations:

• The type of soil you have
• Type of lawn you have
• Watering method / type of irrigation
• The position or aspect of the lawn in the garden
• The season we are in
• How green you want your lawn to be

Soil Type:

The type of soil you have will determine how much water it can hold and how penetrable it is, which is a key piece of information when considering how much water your lawn will need. In fact, understanding your soil is one of the most important things you can do. Generally speaking, clay soil can hold a considerable amount of water for long periods; however, it absorbs water slowly. Sandy soils, on the other hand, can absorb water quickly but do not hold onto it for long.  Using this information, if you have Clay soil, you can water less frequently (because it holds more water), but you’re best to water with a method that delivers water in a slower fashion, like drippers or a mini-rotator type sprinkler such as an Rainbird R-VAN's or Hunter MP rotators.  Water tends to run off clay soils if you apply it too fast and can also pool in low spots. On the contrary, since sandy soils have the potential to absorb water quickly but don’t hold as much, more regular watering would be required for shorter periods of time. It's also important to note here that it is very common for sandy soils to be water-repellant or what is called hydrophobic. Non-wetting soils are very common in Adelaide and lead to a lot of frustration in maintaining your lawn. This problem results in the soil repelling water which means the water you apply simply runs off the soil rather than penetrating through to the root zone. The lawn continues to dry down, regardless of how often you water.  While easily solved, this problem is often overlooked. If you want to read more about this, click here. 

Type of lawn:

Knowing what type of lawn you have can help you know how often and how much. Some lawns are more drought-tolerant than others. For example, lawns like kikuyu, couch and buffalo use far less water than lawns like tall fescue, rye and bluegrass. Kikuyu and Couch are truly drought-tolerant. Once established, there is generally enough natural rainfall in Adelaide to keep them alive, so technically, you don’t need to water them at all! I wouldn’t recommend this type of management, but it goes to show how resilient these types of lawns are and how wide the spectrum of answers to these questions can be. If you don't water at all, lawns like kikuyu and couch will dry out and go brown during the Summer and then recover when the Autumn rains come around.

Typically, lawns like tall fescue, rye and bluegrass are thirsty and don't tolerate their root system drying out. In South Australia, they'll need watering as much as three times per week during summer to keep them happy. 

Lawn Watering method:

The way you water your lawn will often determine how often and how long. The most common ways to water your lawn include pop-up sprinklers, subsurface drippers, hand watering and a movable sprinkler attached to a hose.

• Hand watering (which is inefficient on a lawn) will require you to water the most frequently because you typically won't stand there for long enough to deliver a deep watering.
• Pop-up sprinklers are the most common way to water your lawn. The frequency and length of time you leave them on will depend on the type you use. Traditional pop up's deliver water quickly, so you don’t need to leave them on as long (around 30 minutes per zone is generally enough). Newer technology sprinklers like Hunter MP rotators or Rainbird R-Vans deliver water more slowly and efficiently. It takes these types of sprinklers twice as long to put out the same amount of water as a traditional pop-up, which is one of the main reasons they are a better choice!  MP rotators and R-Vans ultimately use less water and do a much more efficient job of delivering it. 
• Subsurface or underground drippers require you to water often during the warmer months - as much as three times per week. There are many reasons for this, but the main one is that they deliver water so slowly. This can mess with your head a bit when you first install them because you think that you must be using a lot of water, but this isn't the case when the system is installed correctly. Even though you are watering frequently, this is the most efficient watering method, mostly because you are delivering water straight to the root zone and, therefore, avoiding run-off and evaporation on the surface. 
• Movable sprinkler attached to a hose: A lot of people opt for this method as a substitute for a pop-up sprinkler system. This method is surprisingly good as long as you have the time and are prepared to move the sprinkler around your lawn until it is all watered. 

Position in the garden:

This is a no-brainer, but I’ll say it anyway – lawns in the shade will require less water than lawns in full sun, so keep this in mind when deciding how much water to apply.

The season we are in:

Daytime temperatures and the volume and frequency of rain will, of course, play a major role in how much and how often you need to water. Heat affects the evaporation rate in the soil and increases the transpiration rate of the lawn, meaning more water is required. Wind dries out the soil faster, and then there is competition from other plants around the garden vying for the same water.  Obviously, the warmer it is, the more frequently you’ll need to water.

As you can see, there isn’t really a one-size-fits-all answer because circumstances can vary so much – and I haven’t even started on wetting agents! Those who know me know that I have a tendency to talk a lot about wetting agents, and that’s a topic for another day, but I will say this: Wetting agents have the ability to drastically reduce the amount of water you apply to your lawn by ensuring it is evenly and deeply moved into the soil profile!

I know.  I haven’t answered the question… How much and how often…  The real answer is as much as the lawn needs, depending on how green you want it to be. If I had to make some generalisations, most warm-season lawns (couch, kikuyu and buffalo) in South Australia will do their best during the warmer months with around 25mm per week of water to keep them green and lush during the warm months of the year. For a healthy couch, kikuyu or buffalo lawn on soil that absorbs water properly, where you want it to stay green through the summer, it would look something like this:

• Traditional pop-up sprinklers: 30 minutes per zone, once per week
• Mini rotator pop-up sprinklers (MP rotator or RVAN): 60 minutes per zone, once per week
• Sub Surface Drip: Half an hour per zone, three times per week
• Moveable sprinkler attached to a hose: 30 - 45 minutes per area (depending on the sprinkler type), once per week

These lawns will survive on less, but they’ll potentially lose some colour till more water is available again.  When you water, you want to get the soil wet down to about 50mm deep. You can test this by digging a small inspection hole after watering. If it didn’t get down that far, water for longer. If you didn’t get any water penetration at all after watering, check that your soil isn’t non-wetting. By doing this, you soon discover how long you need to water. You’ll also discover how long it takes for your soil to dry out.  For what it's worth, I have a Santa Ana lawn at home that I like to keep lush and green all year round. It's growing in full sun on clay soil. Using a Rainbird Coppershield subsurface drip system, I water twice per week during spring and summer for about half an hour each time, which seems to do the job. My neighbour has a kikuyu lawn and isn't as particular as I am. They have traditional pop-ups and don't use them very often - around once per fortnight, I think. While their lawn isn't as green as mine, it's still alive and presentable.