Water needs of common lawn grasses
Lawn grasses fall into two groups. Warm-season grasses such as bermudagrass, zoysiagrass and St. Augustinegrass grow in hot summers and go dormant in cold weather. Cool-season grasses such as tall fescue, Kentucky bluegrass and perennial ryegrass grow best in spring and fall. As a group, warm-season grasses use considerably less water.
| Grass | Type | Water use | ET rate (in/day) | Drought resistance | Root depth (ft) | Mowing height (in) |
|---|---|---|---|---|---|---|
| Buffalograss | Warm | Very low | under 0.24 | Superior | 1.5–3.0 | — |
| Bermudagrass (common and hybrid) | Warm | Low | 0.24–0.28 | Superior | 1.5–6.0 | 0.5–1.0 |
| Zoysiagrass | Warm | Low | 0.24–0.28 | Excellent | 1.5–2.5 | 0.5–1.0 |
| Seashore paspalum | Warm | Medium | 0.28–0.33 | Excellent | 1.5–5.0 | 0.5–1.0 |
| St. Augustinegrass | Warm | Medium | 0.28–0.33 | Good | 1.5–5.0 | 0.5–1.5 |
| Kikuyugrass | Warm | High | 0.33–0.39 | Good | — | 0.5–1.0 |
| Fine fescues (hard, Chewings, red) | Cool | Medium | 0.28–0.33 | Fair | — | 1.0–2.0 (red fescue only) |
| Perennial ryegrass | Cool | High | 0.33–0.39 | Fair | 0.5–1.5 | 1.5–2.5 |
| Tall fescue | Cool | Very high | over 0.39 | Medium | 1.5–3.0 | 1.5–3.0 |
| Kentucky bluegrass | Cool | Very high | over 0.39 | Fair | 0.5–1.5 | 1.5–2.5 |
| Creeping bentgrass | Cool | Very high | over 0.39 | Fair | 0.3–1.5 | 0.2–0.5 |
| Annual bluegrass | Cool | Very high | over 0.39 | Poor | 0.1–0.3 | — |
| Rough bluegrass | Cool | Very high | over 0.39 | Very poor | — | — |
The ET rates are for well-watered grass in its adapted climate and describe how the species compare with each other. Your lawn's actual water use depends on your local weather, which is where the next table comes in.
How much water each grass type needs per week
Grass water use is estimated from reference evapotranspiration (ETo), the water use of a standard grass surface in your local weather, multiplied by a crop coefficient (Kc). University of California Cooperative Extension uses a Kc of 0.8 for cool-season and 0.6 for warm-season turf for practical purposes, and lower values when water is short:
- Optimum: best growth, quality and appearance.
- Deficit: adequate appearance with less growth, saving at least 25% of the water needed for optimum.
- Survival: just enough to keep the grass alive to recover later; growth and quality drop sharply.
| Grass type and level | Kc | ETo 1.0 in/week | ETo 1.5 in/week | ETo 2.0 in/week |
|---|---|---|---|---|
| Cool-season, optimum | 0.80 | 0.8 in (20 mm) | 1.2 in (30 mm) | 1.6 in (41 mm) |
| Cool-season, deficit | 0.60 | 0.6 in (15 mm) | 0.9 in (23 mm) | 1.2 in (30 mm) |
| Cool-season, survival | 0.40 | 0.4 in (10 mm) | 0.6 in (15 mm) | 0.8 in (20 mm) |
| Warm-season, optimum | 0.60 | 0.6 in (15 mm) | 0.9 in (23 mm) | 1.2 in (30 mm) |
| Warm-season, deficit | 0.40 | 0.4 in (10 mm) | 0.6 in (15 mm) | 0.8 in (20 mm) |
| Warm-season, survival | 0.20 | 0.2 in (5 mm) | 0.3 in (8 mm) | 0.4 in (10 mm) |
Local weekly ETo is published by weather networks and many water utilities; hot, dry, sunny climates have higher values. Other references use higher coefficients for turf kept at full growth. FAO-56, for example, lists 0.95 for cool-season and 0.85 for warm-season turf, and the crop coefficient table lists both.
To run these numbers for your own lawn and local ETo, use the lawn water requirement calculator. For the simpler rule of thumb of about 1 inch per week, use the lawn watering calculator.
How often to water: root depth and soil
How often to water depends on how much water the root zone holds. University of California Cooperative Extension suggests watering when about half of the available water in the root zone has been used. Deep-rooted grasses in soils that hold more water can go longer between waterings.
| Soil texture | Available water (in/ft) | 6 in roots | 12 in roots | 36 in roots |
|---|---|---|---|---|
| Sand | 1.0 | 0.5 in | 1.0 in | 3.0 in |
| Loam | 1.5 | 0.75 in | 1.5 in | 4.5 in |
| Clay loam | 2.0 | 1.0 in | 2.0 in | 6.0 in |
Worked example (from UC Publication 8395)
- Grass and soil: cool-season grass (Kc 0.8) with 12-inch roots in loam holds 1.5 in of available water; half of that is 0.75 in.
- Daily use: with ETo of 0.20 in/day, the grass uses 0.20 × 0.8 = 0.16 in/day.
- Interval: 0.75 ÷ 0.16 = 4.7, so about every 5 days, applying about 0.8 in each time.
UC adds that on clay or compacted soils, where water puddles or runs off, and on sandy soils, where it drains past the roots, it's better to water no less often than every third day with smaller amounts, for example 0.5 in every 3 days instead of 0.8 in every 5. The irrigation interval calculator and lawn watering schedule calculator work this out for your soil.
Water use is not the same as drought resistance
A grass's water use and its ability to survive drought are different traits. Some grasses avoid drought with deep roots and leaves that lose little water; others tolerate it by going dormant or withstanding dehydration. UC Publication 8395 groups the common species like this:
- Low water use and high drought resistance: bermudagrass, seashore paspalum and buffalograss. Buffalograss survives drought by going dormant.
- High water use, medium drought resistance: tall fescue, helped by its deep roots.
- High water use, fair or poor drought resistance: the ryegrasses and bluegrasses.
St. Augustinegrass is a special case: its water use is medium, but it tolerates tissue dehydration well, giving it good drought resistance. In a UC field study at Irvine, the warm-season grasses needed 36 percent less water than the cool-season grasses for acceptable quality.
Mowing, shade and fertilizer
| Factor | Effect on water use | What UC recommends |
|---|---|---|
| Mowing height | Taller grass roots deeper but uses more water; closely mowed turf uses less. | Mow at the tallest height in the species' recommended range, removing no more than one third of the blade. |
| Mowing frequency | Long, infrequently mowed leaves use more water. | Mow regularly at the right height. |
| Shade | Shaded grass needs about half the water of the same grass in full sun in hot summer months. | Water shaded areas less. |
| Nitrogen | More nitrogen means more growth and more water use. | Use the lowest amount in the recommended range during drought. |
| Compaction and thatch | Both reduce how well water gets into the soil. | Aerate and dethatch in spring or fall, not midsummer. |
UC also recommends watering late at night or early in the morning and splitting water into shorter cycles if it starts to run off. See the soil infiltration rate chart for how fast different soils absorb water.
Frequently asked questions
Which lawn grass uses the least water?
Among common lawn grasses, buffalograss has the lowest water use, followed by bermudagrass and zoysiagrass, according to comparative evapotranspiration rates published by University of California Cooperative Extension. Bermudagrass and buffalograss also rank superior for drought resistance.
How much water does bermudagrass need?
University of California Cooperative Extension suggests a crop coefficient of 0.60 for warm-season grasses such as bermudagrass at optimum quality. That means about 0.9 inch per week when reference evapotranspiration is 1.5 inches per week. Bermudagrass ranks superior for drought resistance and roots 1.5 to 6 feet deep, so it tolerates longer gaps between watering than most grasses.
How much water does tall fescue need?
Tall fescue is a cool-season grass with a very high water use rate. University of California Cooperative Extension uses a crop coefficient of 0.80 for cool-season grasses, or about 1.2 inches per week when reference evapotranspiration is 1.5 inches per week. Its roots reach 1.5 to 3 feet, deeper than other cool-season lawn grasses, which gives it medium drought resistance.
How much water does Kentucky bluegrass need?
Kentucky bluegrass has a very high water use rate and only fair drought resistance. Like other cool-season grasses, it needs about 80% of reference evapotranspiration for optimum quality. Its roots are relatively shallow, typically 0.5 to 1.5 feet, so it needs water more often than deep-rooted grasses.
Do warm-season grasses need less water than cool-season grasses?
Yes. University of California research found that warm-season grasses needed 36 percent less water than cool-season grasses for acceptable quality. Warm-season grasses photosynthesize more efficiently and keep growing with their pores partly closed, so they lose less water.
How much less water does a shaded lawn need?
Shaded turf uses noticeably less water. University of California Cooperative Extension notes that in hot summer months, grass in shade generally needs about half as much water as the same grass growing nearby in full sun.
Who built and checked this chart
Licensed Professional Engineer and Irrigation Association Certified Irrigation Designer with more than 20 years in irrigation design, system auditing and landscape water management. Full profile
How this page was checked
- Species rankings, root depths, mowing heights and crop coefficients transcribed from UC Publication 8395 and checked table by table.
- Weekly amounts recalculated as Kc × ETo, and UC's frequency example recalculated by hand.
- FAO-56 turf coefficients checked against FAO-56 Table 12.
Sources
- Harivandi, M. A., Baird, J., Hartin, J., Henry, M. and Shaw, D. (2009). Managing Turfgrasses during Drought. University of California Division of Agriculture and Natural Resources, Publication 8395.
- University of California Center for Landscape and Urban Horticulture. Turfgrass Crop Coefficients (Kc).
- FAO Irrigation and Drainage Paper 56, Crop Evapotranspiration. Chapter 6: ETc, Single crop coefficient (Kc), Table 12.