Deep and Infrequent Watering: Why It Builds Deeper Roots
Light daily watering keeps roots near the surface, while soaking the root zone and then waiting pulls them down into moist soil. This guide shows how deep to water, how long to wait and how to check the result.
By Daniel Reeves, PE, CID
Irrigation Design Engineer
Short answer
Deep and infrequent watering builds deeper roots because roots grow toward wet soil: soak the top 6 to 8 inches (15 to 20 cm), then wait until the lawn shows early stress.1
The wait runs about 7 to 10 days in cool spring and fall weather, 2 to 3 days in summer, and 1 to 2 days on sandy soil in heat. Each watering should reach about 1 inch (2.5 cm) below the deepest roots and no further.2
Most lawn advice stops at “water deeply, not often” and leaves two numbers unstated: how deep deep is, and how long the wait should be. Depth comes from your root zone, the wait comes from your soil and the weather, and the wetting front depth calculator shows how far down a given watering reaches.
Below: why the method builds roots, how to set depth and spacing for your soil, a worked example that ends in minutes on your controller, and how to check the result.
Key takeaways
- Roots follow water. Light sprinkling encourages roots only near the surface, while wetting the top 6 to 8 inches (15 to 20 cm) promotes healthy, deeper roots.1
- Water each time to about 1 inch (2.5 cm) below the deepest roots, which is 7 inches (18 cm) for a lawn with 6-inch (15 cm) roots.2
- Infrequent is relative: about 7 to 10 days in cool weather and 2 to 3 days in summer, with sandy soil needing water every 1 to 2 days.2
- For 6-inch roots, one watering refills about 0.2 to 0.6 inch (5 to 16 mm), depending on the soil.
- Deeper roots stretch the gap. On loam at 0.15 inch (3.8 mm) of daily use, a lawn with 2-inch roots needs water about daily and one with 8-inch roots about every 4 days.
- Check depth with a long screwdriver several hours after watering, and split runs into cycles when water runs off before it soaks in.3
What does deep and infrequent watering mean?
It is two decisions. Depth is how far each watering moves down into the soil. The gap is how long you wait before watering again. Your lawn and soil set both, not a fixed calendar.
For depth, Purdue's Clark Throssell says to apply enough water that it moves to about 1 inch (2.5 cm) below the bottom of the root zone, so a turf with 5-inch roots gets water down to 6 inches.2 Nebraska Extension uses a margin of about half an inch (1.3 cm) and gives 6 inches (15 cm) as the working depth for turf.3 UC says that letting water penetrate the top 6 to 8 inches (15 to 20 cm) promotes healthy roots and makes the best use of water.1
For the gap, Throssell defines infrequent as watering only once the turf begins to show water stress, after the grass has used the water available to it.2 That can mean every 7 to 10 days in cool spring or fall weather, every 2 or 3 days in summer, and every 1 or 2 days on sandy soil in heat.2 All of those count as infrequent, because the lawn has used up its stored water before it is refilled.
Why does deep watering build deeper roots?
Roots take up water only where they grow, so they grow toward water. UC reports that light sprinkling encourages roots only near the soil surface and stunts deeper growth, while wetting the top 6 to 8 inches promotes healthy rooting.1 Purdue adds the feedback loop: water that reaches just below the root zone draws the root system downward, and a lawn with 8-inch roots can draw on more stored water than one with 4-inch roots, so it can go longer between waterings.2
Frequent shallow watering also changes the soil. Nebraska Extension warns that runs of 15 to 20 minutes three or more times a week often leave a shallow layer of constantly wet soil that blocks oxygen from moving down, and roots need that oxygen to keep growing.3
Deep and infrequent
How deep should you water?
Target the bottom of the roots plus a small margin, which means you need your own root depth. It varies with grass species, season, traffic and soil.2 Throssell's example is a putting-green bentgrass with 4-inch roots in spring and only 2-inch roots in midsummer, which drops the target depth from 5 inches to 3.2 Pull a few soil cores, measure to the lowest live root, and use the root zone depth calculator when you need a starting estimate before you dig.
Root depth also sets how much water the soil can store for the grass. Plant-available water runs from about 0.75 to 1.25 inches per foot in sands and loamy sands up to 1.75 to 2.5 inches per foot in clay loams.4 Table 1 uses 1.9 inches per foot for loam, the middle of UC's 1.50 to 2.30 range, and refills half of the stored water at each watering. The half-refill is a planning figure, and the management allowed depletion calculator lets you change it. If you wait for visible stress, as Purdue advises, your gap will usually run longer than the table shows.2
How root depth changes the gap between waterings on loam
| Root depth | Target wetting depth (root + 1 in) | Water stored in root zone | Refill at 50% depletion | Days between waterings at 0.15 in/day |
|---|---|---|---|---|
| 2 in (5 cm) | 3 in (8 cm) | 0.32 in (8 mm) | 0.16 in (4 mm) | About 1 |
| 4 in (10 cm) | 5 in (13 cm) | 0.63 in (16 mm) | 0.32 in (8 mm) | About 2 |
| 6 in (15 cm) | 7 in (18 cm) | 0.95 in (24 mm) | 0.48 in (12 mm) | About 3 |
| 8 in (20 cm) | 9 in (23 cm) | 1.27 in (32 mm) | 0.63 in (16 mm) | About 4 |
Planning values: loam at 1.9 in/ft (the midpoint of the UC range),4 refill at half of stored water, daily lawn water use of 0.15 in (3.8 mm), no rain. Days between waterings = refill ÷ daily use, rounded to the nearest day. Target depth follows Purdue's 1 inch below the roots.2
On the same soil and weather, the lawn with 8-inch roots goes about four times as long between waterings as the lawn with 2-inch roots, because stored water scales with root depth. A lawn watered lightly every day never builds that reserve.1
How often should you water for deep roots?
The gap equals the refill depth divided by daily water use, so it shortens in hot weather and lengthens on soils that store more. Table 2 applies that to a 6-inch root zone at three example use rates: 0.06, 0.15 and 0.25 inch (1.5, 3.8 and 6.4 mm) a day.
Days between deep waterings by soil and weather, 6-inch roots
| Soil | Water held (in/ft) | Refill per watering | Cool spring or fall (0.06 in/day) | Mild summer (0.15 in/day) | Hot, dry summer (0.25 in/day) |
|---|---|---|---|---|---|
| Sands and loamy sands | 0.75–1.25 | 0.19–0.31 in (5–8 mm) | 3.1–5.2 days | 1.3–2.1 days | 0.8–1.3 days |
| Sandy loams | 1.25–1.75 | 0.31–0.44 in (8–11 mm) | 5.2–7.3 days | 2.1–2.9 days | 1.3–1.8 days |
| Loams and silt loams | 1.50–2.30 | 0.38–0.58 in (10–15 mm) | 6.3–9.6 days | 2.5–3.8 days | 1.5–2.3 days |
| Clay loams | 1.75–2.50 | 0.44–0.63 in (11–16 mm) | 7.3–10.4 days | 2.9–4.2 days | 1.8–2.5 days |
| Clays | 1.60–2.50 | 0.40–0.63 in (10–16 mm) | 6.7–10.4 days | 2.7–4.2 days | 1.6–2.5 days |
Water held values are UC plant-available ranges.4 Refill = 0.5 ft of roots × water held × 0.5. Days = refill ÷ daily use, rounded to 0.1. The three daily use rates are example inputs equal to about 0.42, 1.05 and 1.75 in (11, 27 and 44 mm) a week, not forecasts; your local ET sets the real figure. 1 in/ft = 83 mm/m. Very coarse sands hold less, 0.4 to 0.75 in/ft.4
The loam row is close to Purdue's field numbers: 6 to 10 days in cool weather against Purdue's 7 to 10, and 1.5 to 3.8 days in summer against its 2 to 3.2 Sand in hot weather works out to about daily, near Purdue's 1 to 2 days.
Grass type moves the answer too. UC says warm-season grasses have extensive root systems and usually need water only 1 or 2 times a week, while cool-season grasses such as tall fescue root less deeply and are scheduled as about 3 equal waterings spread across the week, fewer in cooler months.5 The irrigation interval calculator turns your soil and daily use into a gap, the lawn watering schedule calculator adds minutes per zone, and the lawn watering by grass type chart compares species.
Tip: stretch the gap one day at a time
If the lawn turns a duller green, wilts or holds footprints before the next watering, apply more water at the next one rather than watering more often.3 Once it passes those checks with a longer gap, stretch it again.
How to set up deep watering: formula, steps and example
Formula
Days between waterings = refill depth ÷ daily water use
Refill depth = root depth (ft) × water held per foot × 0.5. Minutes per watering = refill depth ÷ DU ÷ precipitation rate × 60. DU is distribution uniformity as a decimal, taken from a catch-can test.
- Measure root depth. Pull several soil cores and measure down to the lowest live roots.2 Typical turf roots reach 6 to 8 inches (15 to 20 cm).1
- Find the refill depth. Multiply root depth in feet by your soil's water held per foot, then by 0.5. The available water capacity calculator estimates the water held when you do not know your soil.
- Measure sprinkler output. Run a catch-can test to get precipitation rate in inches per hour and DU. Purdue uses the same catch-can method to learn how much water a run applies.2
- Convert to minutes. Divide the refill depth by DU, then by the precipitation rate, and multiply by 60. The how long to water lawn calculator does this for each zone.
- Verify with a probe. Check the wetted depth several hours after a run and adjust the minutes until moisture reaches the target depth.2
Enter your soil and the water applied. The calculator returns the wetting depth to compare with your root depth.
Take a 4,000 sq ft lawn on loam with 6-inch roots in a mild summer. Rotors apply 0.5 inch an hour, a catch-can test gives a DU of 0.75, and runoff begins after about 30 minutes.
- Root depth (soil cores)6 in = 0.5 ft
- Water held, loam1.9 in/ft
- Water stored in the root zone0.5 × 1.9 = 0.95 in
- Refill depth at 50% depletion0.95 × 0.5 = 0.475 in
- Daily use, mild summer0.15 in/day
- Days between waterings0.475 ÷ 0.15 = 3.2, use 3
- Water to apply0.475 ÷ 0.75 = 0.633 in
- Minutes at 0.5 in/hr0.633 ÷ 0.5 × 60 = 76 min
- Cycles before runoff (30 min)76 ÷ 30 = 2.5, use 3 of about 25 min
- Volume per watering4,000 × 0.633 × 0.623 ≈ 1,580 gal
Every 3 days, 76 minutes in 3 cycles of about 25 minutes
Metric: the 0.475 in refill is 12 mm, the 0.633 in applied is 16 mm, and each watering is about 5,980 liters over 372 m².
Check the plan against the soil. Three days at 0.15 inch is 0.45 inch of use, just under the 0.475 inch refill, so the roots are watered before they pass half depletion. Because DU is 0.75, the driest part of the lawn still receives the full 0.475 inch and the better-covered areas receive more, which supplies the small margin below the roots that Purdue recommends.2
How to check that water is going deep
A long-bladed screwdriver is the simplest depth gauge. Nebraska Extension recommends a blade about 12 inches (30 cm) long or more. It slides easily through moist soil and resists in dry soil, so after a watering you push it down until you meet a layer of greater resistance and measure the moist depth.3 Use the same screwdriver each time so you learn what the resistance feels like.
Wait several hours after the run before checking, because water takes time to move down through the soil.2 If moisture stops short of your target depth, add minutes. If it reaches well past the roots, shorten the run, since water below the root zone is lost to the grass.2
Between waterings, the lawn tells you when the gap has run long enough. Nebraska Extension lists three signs of dry turf: a duller green in place of bright blue-green, wilting blades, and footprints that stay after you walk across the grass.3
How to water deeply on clay, slopes and compacted soil
Deep watering fails when water leaves the lawn before it goes down. Intake rates swing widely by soil: a coarse sand can take in up to 10 inches (250 mm) an hour, while a clay can take in less than 0.05 inch (1.3 mm) an hour.6 A rotor putting down 0.5 inch an hour onto that clay delivers ten times what the soil accepts, and the excess runs off or ponds.
The fix is cycle and soak. Run each zone only until runoff is about to start, then repeat the run later the same day so the first pass soaks in and the second pushes it deeper.3 The cycle and soak calculator sets the run length and the pause, and the soil infiltration rate chart gives typical intake rates to compare with your sprinkler.
When deep watering is the wrong move
New seed and fresh sod are the exception. UC says light sprinkling helps only newly planted turf, whose roots are still in the very top of the soil, and that watering should deepen as the roots extend.1 The grass seed watering calculator sets a day-by-day taper for a new lawn.
Heat and shallow soil also change the plan. Roots retreat in midsummer, so re-measure them and shorten the target depth.2 UC says desert areas, slopes and shallow soils need shorter, more frequent irrigations than the usual warm-season schedule.5
Check local rules first
Municipal watering-day limits take priority over any schedule here. If your days are fixed, keep the depth per watering and fit the gap to the days allowed. Large, commercial and agricultural systems need a design or audit rather than a homeowner rule.
Frequently asked questions
Is it better to water a lawn every day or once a week?
Neither number is a rule. A lawn with 6-inch roots on loam can often wait 2 to 4 days in summer and 6 to 10 days in cool weather, while sandy soil in heat may need water every day or two. Daily light watering is the pattern to avoid, because it leaves roots near the surface.
How many inches of water is deep watering?
Enough to refill the root zone, which for 6-inch roots is about 0.2 to 0.6 inch (5 to 16 mm) per watering depending on the soil, from sand at the low end to clay loam at the high end. Apply a little more where sprinklers cover unevenly, then confirm the depth with a probe.
Can you water too deeply?
Yes. Water that moves below the root zone no longer helps the grass, which is why Purdue recommends stopping at about 1 inch (2.5 cm) below the deepest roots. Nebraska Extension uses about half an inch (1.3 cm). Check with a probe a few hours after watering and shorten the run if moisture reaches well past the roots.
Does deep watering work on sandy soil?
Yes, with a shorter gap. Sands and loamy sands hold only about 0.75 to 1.25 inches of water per foot, so a 6-inch root zone refills about 0.2 to 0.3 inch and runs through its supply in about a day in hot weather. Water to the same depth, just more often, and check with a probe.
How long should sprinklers run for deep watering?
Divide the water you need by the sprinkler's precipitation rate and multiply by 60. For 0.45 inch, a spray head at 1.5 inches an hour needs 18 minutes and a rotor at 0.5 inch an hour needs 54 minutes. Add time where coverage is uneven, and split long runs into cycles when water starts to run off.
Does deep watering suit every grass type?
The principle holds, but the gap changes. UC says warm-season grasses have extensive deep roots and usually need water only 1 or 2 times a week. Cool-season grasses such as tall fescue are scheduled at about 3 equal waterings a week. Soil, slope and weather move both numbers, so confirm with a probe.
Sources
- UC Statewide IPM Program. How to Water: Water Deep and Infrequently. The UC Guide to Healthy Lawns. University of California Agriculture and Natural Resources.
- Throssell, C. Irrigation Scheduling for Turf Sites. Department of Agronomy, Purdue University. Michigan State University Libraries, Turfgrass Information Center archive.
- Browning, S. Deep, Infrequent Irrigation Makes Lawns and Trees Healthier. Nebraska Extension in Lancaster County, NEBLINE newsletter, July 2024. University of Nebraska-Lincoln.
- UC Center for Landscape & Urban Horticulture. Soil Water Holding Characteristics. University of California Agriculture and Natural Resources. Adapted from Schwankl and Prichard (2009).
- UC Statewide IPM Program. How Many Times a Week to Water. The UC Guide to Healthy Lawns. University of California Agriculture and Natural Resources.
- Clark, C.A. The Important Role of Soil Texture on Water. Crops and Soils, University of Wisconsin-Madison Division of Extension.
Written by Daniel Reeves, PE, CID. Figures in this article were calculated from the cited sources and checked against our lawn watering calculator. Read how we calculate and our editorial policy. Spotted an error? Tell us.