How much water does a lawn actually need?

Enough to wet the soil properly, occasionally — not a little every evening. The shallow habit is the one that does harm.

Why deep and infrequent

Roots follow water. A lawn watered lightly every day never has moisture below the top few centimetres, so the roots stay there, and a lawn rooted in the top few centimetres is a lawn that wilts the moment watering stops.

A thorough soak every few days puts water deeper, and the roots follow it down. That lawn survives a dry fortnight.

How much is “enough”

The common rule of thumb for an established lawn in dry weather is in the region of 15 to 25 litres per square metre per week, in one or two applications rather than seven. That is a rule of thumb rather than a standard: soil type changes it enormously — a sand holds almost nothing and a clay holds a great deal.

The measurement worth making once

Put four straight-sided containers — tins, jars, anything identical — around the area a sprinkler covers. Run it for twenty minutes. Measure the depth in each.

That gives you two things at once. The rate, in millimetres per twenty minutes, which converts directly to litres per square metre and tells you how long to run it. And the evenness, which is usually the surprise: most sprinklers deliver much more near the head than at the edge of their claimed radius.

What the listings claim

A sprinkler’s coverage figure is an area at a stated pressure, and the pressure is the part that gets dropped. A sprinkler fed by a rain barrel and a sprinkler on mains pressure are not the same machine, and the coverage figure was obtained on the second.

How this site handles it

Sprinkler pages here print the coverage figure with the pressure the maker states it at, and say so when the maker states none. Pump pages print flow at zero head, which is the convention, and say that it is — because between the two figures sits the question of whether your sprinkler will turn at all.

Wherever this page and the maker’s own documentation disagree, the documentation wins. Every cutting width, cutting height, stated area, pack capacity, flow rate, head, sound level and application rate on this page comes from the maker’s own published figures, with the unit as printed and the source named. None of it is measured here, and no figure is converted into another convention, because a converted number is a different number. And the operating point this page always states: a pump’s flow figure is measured at zero head and its head figure at zero flow. Neither point is anywhere near where a garden hose runs, and the two cannot happen at once. This page reports both with the convention named, and reports a sprinkler’s coverage with the pressure it was obtained at — or with the fact that none was stated.