How much and how often should I water a lawn?

Less often than most people do, and far more deeply each time. The single most common lawn watering mistake is a light sprinkle every day, which is worse than not watering at all.

The target is roughly 25mm of water per week including rainfall, delivered in one or two sessions rather than daily. That much soaks down 10–15cm, which is where you want the roots.

The reason frequency matters is root depth. Grass roots grow toward moisture. Water lightly and often and the moisture only ever sits in the top 2cm, so the roots stay there — producing a lawn with a shallow root system that cannot survive a dry spell and is dependent on constant watering. Water deeply and infrequently and the roots follow the water down, producing a lawn that copes with drought.

Measuring it is easier than it sounds. Put a few straight-sided containers on the lawn while the sprinkler runs and time how long it takes to collect 25mm. That gives you your run time, once, for good.

Water in the early morning. The grass dries during the day, which matters because foliage left wet overnight is much more susceptible to fungal disease. Midday watering loses a substantial share to evaporation.

Established lawns rarely need watering at all in temperate climates. Grass going brown in a dry summer is usually dormant rather than dead, and greens up within a couple of weeks of rain. Newly laid turf and new seed are different and do need consistent moisture until established.

Raising the mowing height during dry weather helps more than watering — longer grass shades its own roots and holds moisture.