Watering your lawn: how much, how often and when
Watering is less about whether you water and more about how. A lawn that gets a few minutes of sprinkler every evening stays shallow-rooted and becomes vulnerable. A lawn that gets water infrequently but deeply roots deeply and copes much better with heatwaves. Here you can read how much water your lawn really needs, when you should water and how to tell that it is time.
In short
- Water infrequently and deeply: usually 10 to 20 litres per square metre per watering.
- Ideally early in the morning. In the evening the leaves stay wet overnight, which encourages fungal diseases.
- Water as needed, not by the calendar. The footprint test and a rain gauge tell you when it is time.
- Sandy soils need smaller amounts more often, loamy soils larger amounts less often.
- If the water does not soak in, the problem lies in the soil. Then aeration helps more than extra water.
How much water does a lawn need?
One litre per square metre equals one millimetre of rainfall. In midsummer a lawn loses about 3 to 5 millimetres a day through the soil and leaves, more on hot, windy days. Over a week that adds up to 20 to 35 litres per square metre, including rain.
What matters is that the water reaches the root zone. Most lawn roots sit in the top 10 to 15 centimetres. One watering should therefore moisten the soil down to this depth. Under trees and along hedges you need more, because the woody plants compete with the lawn for water.
How often to water? It depends on the soil
How much water the soil can store determines the rhythm. Sand holds little water, loam a lot. The values in the table are guidelines for midsummer without rain.
| Soil type | Water storage | Amount per watering | Rhythm in midsummer |
|---|---|---|---|
| Sandy | low, water drains away quickly | about 10 l/m² | every 2 to 3 days |
| Sandy loam (typical garden soil) | medium | about 15 l/m² | every 4 to 5 days |
| Loamy to clay | high, but water soaks in slowly | about 20 l/m², in two rounds | about once a week |
Why infrequent and deep is better
Roots grow where the water is. If you only moisten the top layer of soil every day, the roots stay shallow. The lawn then depends entirely on you and dries out as soon as you miss a few days. On top of that, a permanently moist surface encourages moss, weed germination and fungal diseases.
If you water less often but thoroughly, the surface dries out in between while water remains deeper down. The roots follow the water downwards. The result is a lawn that copes well with a week without water.
When to water: morning is best
| Time | Rating | Why |
|---|---|---|
| Early morning, about 4 to 8 am | ideal | little evaporation, little wind, the leaves dry off during the day |
| Late morning | good | somewhat more evaporation, the leaves dry quickly |
| Midday in the sun | possible, but inefficient | some of the water evaporates before it reaches the soil |
| Evening and night | unfavourable | the leaves stay wet until morning, which encourages fungal diseases |
The idea that water droplets act like magnifying glasses in the midday sun and burn the lawn is a myth. Watering at midday does no harm; you just lose more water. Why leaf wetness overnight is a problem is explained in Identifying and treating lawn diseases.
How to tell that your lawn needs water
- Footprint test: if your footprints are still clearly visible after a few minutes, the grass lacks water.
- Colour: the lawn turns dull and bluish-grey before it turns brown.
- Leaves: the blades roll up to lose less water.
- Soil sample: take a sample with a spade or a hollow spoon. If the soil is dry at a depth of 5 to 10 centimetres, you should water.
A simple rain gauge in the garden also helps you judge how much rain has actually fallen. A short shower of 2 or 3 millimetres does not replace watering.
How to measure the amount of water
Few people know how much water their sprinkler delivers per hour. It is easy to find out.
The cup test
- Place several shallow containers with straight sides across the area, for example empty tins.
- Let the sprinkler run for 30 minutes.
- Measure the water depth in the containers with a ruler. 1 millimetre equals 1 litre per square metre.
- Work out how long you need for your target amount. Large differences between the containers also show you where the sprinkler distributes unevenly.
Many oscillating sprinklers only deliver a few millimetres per hour. 15 litres per square metre can therefore take an hour or longer. If you want to be more precise, fit a water meter between the tap and the hose. Which sprinklers suit which area is explained in The right irrigation system.
When the water does not soak in
If puddles form when you water or the water runs off to the side, more water will not help. The cause then lies in the soil:
| Sign | Possible cause | What helps |
|---|---|---|
| Water stands on the surface after a short time | compacted soil | water in two rounds with a break, aerate and top-dress with sand in the medium term |
| Water soaks in poorly, the lawn feels spongy | thatch | reduce thatch, dethatch or scarify |
| After a long drought water beads up, the soil underneath stays bone dry | water-repellent soil | open up the soil, water slowly and in several rounds |
| Water runs off on a slope | gradient | smaller amounts, several in a row instead |
More on this in When soil repels water and Lawn aeration.
Watering through the year
| Phase | What the lawn needs |
|---|---|
| Spring | rain is usually enough. Only water during longer dry spells, and then deeply. |
| Summer | the main season for watering. Water according to soil type, see the table above. |
| Autumn | evaporation drops considerably. Only water after a dry late summer or after a renovation. |
| New sowing and overseeding | the exception to the rule: during germination keep the surface constantly moist, so small amounts several times a day. Once the seedlings have emerged, gradually switch to less often and more. More on this in Sowing a lawn. |
| Winter | no watering needed |
Drought: water or let it go dormant?
Lawn grasses can survive long dry spells by going into summer dormancy. The lawn turns brown, but the crown at the base of the plant stays alive. After the first heavy rain it starts growing again. So you can consciously decide not to water in midsummer.
What matters is that you then stick to your decision. Constantly switching between watering and drying out costs the lawn more strength than one continuous dormant phase. During dormancy: do not fertilise, keep foot traffic low and only mow when something has really grown back. On very light sandy soils and with newly laid lawns, dormancy is riskier. There you should water at least enough that the grasses do not dry out completely.
Our guest author NewWonder555 has written up further experience with watering during droughts: Watering the lawn during drought.
Check local rules
In dry summers, many districts and municipalities issue general orders. Often, taking water from streams, rivers and ponds is then banned, and sometimes watering lawns with mains water at certain times of day. Before you start the pump during a drought, it is worth checking your municipality's website.
How your lawn can get by with less water
- Use rainwater: a water butt or cistern saves mains water. Rainwater is well suited to lawns.
- Keep the soil free-draining: aerating and top-dressing with sand make sure that rain and irrigation water go down deep instead of evaporating at the surface.
- Keep thatch under control: a thick layer of thatch holds water at the top and lets it evaporate there.
- Use a potassium-rich fertiliser in late summer: potassium strengthens the cell walls and helps the lawn cope with drought stress.
- Mow less often during heatwaves and no lower than usual. Under drought stress, better skip a week.
- Cut cleanly: frayed blades from a blunt blade dry out at the tips and turn brown.
Good to know
A reel mower cuts the grass off cleanly like scissors. The tips do not fray and stay green. Why that is so is explained in Reel mower: what it does better than a rotary mower.
Common watering mistakes
| Mistake | Better |
|---|---|
| A short sprinkle every evening | less often and deeply, in the morning |
| Watering by the calendar | as needed, with the footprint test and a rain gauge |
| Carrying on watering although water runs off | take a break and water in two rounds, open up the soil in the medium term |
| Mowing and fertilising under drought stress | wait until the lawn is growing again |
| Constantly switching between watering and drying out | either water consistently or consciously let the lawn go dormant |
Frequently asked questions about watering
How long does the sprinkler need to run?
That depends on the sprinkler. The cup test tells you how many millimetres it delivers per hour. For 15 litres per square metre it is an hour or more with many sprinklers.
Can I water in the sun?
Yes, it does not harm the lawn. More water just evaporates. Early morning is still the better time.
Mains water or rainwater?
Both work. Rainwater is low in lime and saves mains water. Well water is also suitable as long as it is not high in iron, otherwise it can leave brown stains on paths and patios.
How long can a lawn survive without water?
An established lawn on normal soil survives several weeks of drought in dormancy. Young lawns and lawns on sandy soil can take much less.
Do I need to water in autumn and winter?
Not in winter. In autumn only during a longer dry spell or if you have just overseeded.
Tools for soil that takes up water
- Lawnpecker: aerating with spoons so that water gets down deep.
- REWUKIL: for dethatching and against thatch.
- Falkenstein: a clean scissor cut with clean cut edges.
