How much water does a lawn need?

Watering is where most lawns are won or lost. Too little and the lawn browns; too much and you waste water, wash nutrients out of the soil, and invite weeds and disease. The right amount depends on your climate, the season, your soil and your grass, so this guide shows you how to work it out for your lawn rather than giving one number for everyone.

Start with a benchmark

Water Corporation gives Perth and South West gardeners a clear benchmark: 10 mm of water, twice a week in summer, and far less in the cooler months, because evaporation drops. It also notes that watering more than this doesn’t help, and overwatering can leach nutrients from the soil.

If your water authority publishes guidance for your area, use that. If not, the Perth figure is a reasonable starting point for a summer week in a warm, dry spell, which you then adjust by watching the lawn. Perth’s sandy soils and hot, dry summers make it a demanding place for lawns, so many lawns elsewhere need no more, and often less.

Why millimetres matter

Rain gauges, weather reports and good watering advice all use millimetres. One millimetre of water spread over one square metre is one litre, so 10 mm over a 100 m² lawn is about 1,000 litres. Thinking in millimetres lets you:

• compare rainfall with what your sprinklers apply;
• set run times from a measurement instead of a guess;
• see how much water your lawn really uses over a season.

Your sprinklers apply water at their own rate, so you need to know how many millimetres your system delivers per minute. That’s what a catch-cup test tells you. See the catch-cup test guide, then use the Sprinkler Run-Time Calculator to turn your target into minutes for each zone.

Adjust for your conditions

Season. Lawns use far more water in summer than in winter. In cooler months, warm-season grasses slow down or go dormant, and many lawns need little or no irrigation.

Weather. Hot, dry, windy days pull water out fast. After good rain, skip watering. A rain gauge in the garden shows exactly how much fell on your lawn.

Soil. Sandy soil drains quickly and holds little water, so it may need smaller amounts more often, and it can turn water-repellent when dry. Clay holds more water but takes it in slowly; apply it in shorter cycles so it soaks in rather than running off. Loam sits in between.

Sun and shade. Lawns in full sun use more water than shaded ones, although tree roots in shade can take much of what you apply.

Slope. Water runs off slopes before it soaks in. Use shorter cycles with a break between them.

Grass type. The Turf Growers Association of WA describes buffalo, couch, kikuyu and zoysia as drought tolerant. Established warm-season lawns can survive dry spells by slowing down or browning off, then recover when water returns.

By grass type

These are general patterns; varieties differ. Your turf supplier can tell you about the variety you have.

By season

• Summer: the main watering season in most of Australia. Water deeply on your allowed days, early in the morning, and watch for dry patches.
• Autumn: reduce gradually as the weather cools. Lawns still growing in autumn benefit from steady moisture.
• Winter: many lawns need little or none. In Perth, sprinklers are switched off from June to August. Hand-water only if the lawn shows stress and your local rules allow it.
• Spring: increase gradually as growth picks up. Spring is the time to check your sprinklers and fix coverage before the heat arrives.

In the tropics, the pattern follows the wet and the dry instead: little or no watering in the wet season, and regular deep watering through the dry.

Water deeply, less often

Applying the full amount in one session (or two short cycles on heavy soil) wets the soil more deeply. Roots follow the water down, which helps the lawn get through hot spells. Watering a little every day keeps roots near the surface and the lawn dependent on you.

To check how deep water is going, push a screwdriver or soil probe into the lawn a few hours after watering. It slides easily through moist soil and stops when it hits dry soil. If the moist layer is shallow, water a little longer next time; if water is running off before the run finishes, split it into two shorter cycles an hour apart instead.

Water early

Water early in the morning: less water is lost to evaporation and wind, and leaves dry off during the day, which reduces the conditions fungal diseases need. Evening watering leaves leaves wet overnight. Check your local rules for allowed days and times.

Make sure water soaks in

Water that runs off or beads on the surface is wasted. Water Corporation notes that WA’s sands are often water-repellent, and that dry patches often mean uneven watering. If water isn’t soaking in:

• test the soil with a few drops of water in a dry patch;
• core aerate compacted areas;
• apply a wetting agent at the label rate;
• split long run times into shorter cycles.

The hydrophobic soil guide covers this in detail.

New lawns

New turf and seed need far more frequent watering while they establish. Water Corporation advises watering new turf three times a day for the first week, then reducing gradually over a period of weeks as the roots grow. In Perth and other areas with a roster, you can apply for an exemption to water a new lawn outside your days. See the watering new turf and seed guide.

Read the lawn

• Needs water: leaves fold or turn bluish-grey, footprints stay flat, soil is dry a few centimetres down.
• Too much: soil is soggy days later, water runs off, moss and weeds appear, and disease is more common.
• Dry patches despite watering: check sprinkler coverage with a catch-cup test, and test for water-repellent soil.
• Brown but alive: in a long dry spell, warm-season grasses may brown off to survive. Tug a handful: if the runners and roots are firm, it will usually recover when water returns.

Watering without an in-ground system

Plenty of good lawns are watered with a hose. To do it well:

• Use a sprinkler, not a hand-held spray, for the main watering. Hand watering rarely puts down enough water evenly; a hose-end sprinkler left in place does.
• Measure it too. Put a few straight-sided cups in the sprinkler’s pattern and time how long it takes to collect your target depth.
• Move it on a pattern so each spray area overlaps the last, and note where you put it.
• Use a tap timer so the sprinkler turns off on time. Check your local rules: some allow hand-held hoses at any time but restrict sprinklers to certain hours.
• Hand-water only the dry spots between main waterings.

Ways to use less water

• Mow a little higher in summer. Longer leaves shade the soil and roots.
• Fix leaks and broken sprinkler heads straight away. A single broken head can waste a lot of water and leave part of the lawn dry.
• Fix coverage, not run times. Running every zone longer to reach one dry corner overwaters everything else.
• Group areas by need. Shaded lawns, sunny lawns and garden beds belong on separate zones.
• Add a rain sensor or a smart controller so the system skips watering after rain.
• Go easy on fertiliser in summer. Feeding pushes growth that needs more water.
• Use rainwater from a tank where your local rules allow. See the rainwater and greywater guide.

Stay within the rules

Every Australian city has water rules, and many have permanent rules about when sprinklers can run. They change with the season and with dam levels, so check your water authority’s current rules before you set a timer. The Bureau of Meteorology also keeps a national search of water restrictions by area. The watering under restrictions guide links each city’s official page.

A quick plan

1. Find your benchmark: your water authority’s advice, or the Perth figure as a summer starting point.
2. Do a catch-cup test on each sprinkler zone.
3. Set run times with the calculator, splitting them into cycles on clay or slopes.
4. Water early on your allowed days, and skip after good rain.
5. Check depth with a screwdriver and watch the lawn; adjust each fortnight through summer.
6. Fix dry patches with better coverage and, if needed, a wetting agent.

Track it

Log watering in your Lawn Journal. Over a season, you’ll see what your lawn actually needs and how it responds, and next summer’s settings will be a starting point rather than a guess.