How much water does an orchard tree need per day?
A tree's daily water use is the depth of water it loses to evaporation and transpiration, spread over the ground area assigned to it. Weather sets the starting point. Reference evapotranspiration (ETo) is the water loss of a well-watered reference grass, reported by weather stations. Multiplying it by a crop coefficient (Kc) gives crop evapotranspiration (ETc) for your crop. Then the calculator scales for canopy size and converts a depth of water over one tree's spacing area into gallons or liters.
Kc values are usually published for mature, full-canopy orchards. UC Cooperative Extension notes that young trees use less water, so a canopy factor (Kr) is applied when the canopy shades less than 60% of the ground. Michigan State University Extension also writes orchard water use as ET times crop coefficient times the area covered, then divides the per-acre result by trees per acre.
| Crop | Kc | Source and note |
|---|---|---|
| Olive, hedgerow | 0.65 | UC guide, California; suggested for the entire season. |
| Olive, vase-shaped | 0.75 | UC guide, California; suggested for the entire season. |
| Citrus, mature | about 0.65 to 0.70 | UC guide; the preset fills 0.70, the top of the range. |
Check local rules first. Water districts, groundwater programs and well permits may set allocations or reporting requirements that take priority over a calculated amount.
How this orchard irrigation calculator works
The calculator finds crop water use in inches or millimeters per day, multiplies by the ground area per tree, adjusts for efficiency, and divides by the flow reaching the tree to get a run time. It uses crop coefficient and reference ET values you supply.
1. Canopy factor (Kr)
Kr from shaded ground
Kr = 2 × fc, capped at 1
fc = π × (canopy diameter)² ÷ 4 ÷ area per tree
fc is the fraction of ground shaded at midday (percent shaded ÷ 100). The equation is from the olive chapter of UC's young orchard guide. For a mature canopy shading 60% or more, Kr = 1. In the diameter option, fc is capped at 1 where canopies overlap. The cap at 1 is this calculator's choice.
2. Crop water use
ETc
ETc = ETo × Kc × Kr
A weekly ETo is divided by 7 first. The result is in in/day (US) or mm/day (metric).
3. Volume per tree
US units
Gallons per tree per day = ETc (in/day) × Row spacing (ft) × Tree spacing (ft) × 0.623 ÷ Efficiency
One inch over one square foot is 144 cubic inches, and a US gallon is 231 cubic inches, so 144 ÷ 231 ≈ 0.623.
Metric units
Liters per tree per day = ETc (mm/day) × Row spacing (m) × Tree spacing (m) ÷ Efficiency
One millimeter over one square meter is exactly one liter. Efficiency is entered as a percent and used as a fraction (90% = 0.90).
4. Run time
Hours per day
Hours = Water per tree per day ÷ (Emitters per tree × Flow per emitter)
Flow is in gph (US) or L/h (metric). Multiply hours by 60 for minutes.
Conversions and rounding
1 in = 25.4 mm, 1 ft = 0.3048 m and 1 US gal = 3.785 L. Switching units converts your entries and returns the same physical answer. Water volumes are estimates, so they are shown as "about": under 10 gallons or liters to 0.1, and otherwise to the nearest whole unit. Depths and factors are shown to the precision used in the math.
When this calculator isn't the right tool
- A single yard tree, where the goal is a soak rather than an orchard spacing. See the tree watering calculator.
- Choosing how many emitters a tree needs. See the tree drip emitter calculator.
- Vines. See the vineyard irrigation calculator.
- Acre-based planning for whole blocks. Start from the agriculture calculators.
Orchard irrigation calculation examples
A young hedgerow olive block is spaced 18 ft between rows and 12 ft between trees. ETo is 0.25 in per day, Kc is 0.65 and the canopy shades 30% of the ground. Each tree has two 1 gph drip emitters.
- Kr: 2 × 0.30 = 0.60.
- ETc: 0.25 × 0.65 × 0.60 = 0.0975 in/day.
- Area per tree: 18 × 12 = 216 sq ft.
- Water: 0.0975 × 216 × 0.623 (exactly 144 ÷ 231) = 13.13 gal, shown as about 13 gallons per tree per day.
- Run time: 13.13 ÷ (2 × 1) = 6.56 hours, shown as about 6 hr 34 min per day.
The same calculation in metric
A mature citrus block is spaced 6 m by 4 m with ETo of 6.5 mm per day, Kc of 0.70 and a 90% system efficiency. Each tree has one micro-sprayer rated at 30 L/h.
- Kr: mature canopy, so 1.
- ETc: 6.5 × 0.70 × 1 = 4.55 mm/day.
- Area per tree: 6 × 4 = 24 m².
- Water: 4.55 × 24 ÷ 0.90 = 121.33 L, shown as about 121 liters per tree per day.
- Run time: 121.33 ÷ (1 × 30) = 4.04 hours, shown as about 4 hr 3 min per day.
How to use the result in the orchard
Getting good inputs
Use a daily ETo from a station close to the orchard. In California, CIMIS stations publish daily ETo, and some UC Cooperative Extension offices publish weekly crop water use reports you can use as ETc directly. Update ETo and Kc through the season, since the calculator gives one day's water for the values entered. One UC table lists mature pistachio Kc values that run from 0.07 to 1.19 across a season, so a single Kc will not fit every month for every crop.
Check the calculation in the field
UC guidance treats calculated ETc as a guideline and recommends confirming it with soil moisture or plant water-status monitoring. If readings show the trees running drier or wetter than intended, adjust Kc, canopy or run time rather than trusting the first number. The management allowed depletion calculator covers how far the soil can dry between irrigations.
Common mistakes
- Using a mature Kc for young trees without a canopy factor, which overstates their water use.
- Entering a weekly ETo as if it were daily. Set the "ETo is given per" selector.
- Forgetting that rain, leaching and soil storage are separate. See the effective rainfall calculator and the leaching requirement calculator.
- Using a nameplate emitter flow without checking it. Compare it to a measured catch.
Factors that change orchard water needs
| Factor | Effect on water needs | What to adjust |
|---|---|---|
| Tree age and canopy | Water use rises as canopies shade more ground. UC notes ET generally peaks once canopies shade about 50% to 60% of the floor. | Update the canopy input as trees grow. |
| Crop and season | Kc changes with crop, cultivar and time of year. | Use a local Kc for the current period. |
| Weather | ETo follows sun, wind, temperature and humidity. | Enter recent ETo, not a long-term average. |
| Orchard floor cover | MSU Extension notes that grass or other plants between rows also transpire and use soil moisture. | Raise Kc if cover crops are actively growing. |
| Wetted area | UC lists typical wetted areas of 20 to 30% (single-line drip), 20 to 50% (double-line drip) and 30 to 60% (micro-sprinkler). This calculator spreads water over the full spacing area. | Place emitters or sprayers over the active root zone. |
| System uniformity | Uneven application means some trees get less water than others. | Enter an efficiency from an evaluation. See the emission uniformity calculator. |
| Canopy method | Methods differ. At 40% shade, Kr = 2 × 0.40 = 0.80, while UC's walnut table gives 67% of mature ETc. | For walnut, compare with the age-based factors in the UC guide. |
Micro-sprayers and drip lines have their own sizing rules. The micro-spray calculator covers those for the emitter side.
Frequently asked questions
How many gallons of water does an orchard tree need per day?
It depends on your weather, crop, canopy size and tree spacing, so there is no single number. This calculator multiplies daily ETo by the crop coefficient, a canopy factor and the ground area each tree covers, then converts inches over that area to gallons. A young tree with a small canopy can need a small fraction of what a mature tree on the same spacing needs.
What is the canopy cover factor (Kr)?
Kr scales a mature-orchard crop coefficient down for trees whose canopies shade only part of the ground. This calculator uses Kr = 2 × the fraction of ground shaded at midday, capped at 1, from the olive chapter of UC Cooperative Extension's guide to young orchards, which applies Kr to canopies shading less than 60% of the ground. Mature, full-canopy orchards use Kr = 1.
Where do I get ETo and Kc values?
ETo comes from a nearby weather station. In California, CIMIS stations publish it daily, and some extension offices publish weekly crop water use reports. Kc comes from a published table for your crop and growth stage, or from a local ET report. The crop presets here cover only a few crops, so use local values when you have them.
See the crop coefficient calculator and the evapotranspiration calculator.
How do I turn gallons per tree into run time?
Divide the daily gallons per tree by the total flow delivered to that tree, which is the number of emitters or micro-sprayers times the flow of each one. For example, 13 gallons a day through two 1 gph emitters takes about 6.5 hours. Use manufacturer flow data or a measured catch, and check that pressure at the emitters is in the range they are designed for.
Should I add extra water for an uneven system?
Yes, if your system doesn't apply water evenly. UC guidance divides the net water requirement by system application efficiency to get the gross requirement. Enter an efficiency from a system evaluation. If you leave it blank, the calculator assumes 100%, which is the smallest amount it can suggest.
Does this calculator include rain, leaching or soil moisture?
No. It estimates the crop's daily water use only. Subtract effective rainfall, add any leaching water your water quality calls for, and adjust for stored soil moisture separately. Soil moisture or plant water-status monitoring can show whether the calculated amount suits your orchard.
Who built and checked this calculator
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
- ETc, canopy factor and volume formulas traced by hand through five test cases in both unit systems.
- Kc values and canopy guidance checked against the UC and MSU sources below.
- Both worked examples match the calculator's output.
Sources
- Mohamed, A. (Ed.). UC Cooperative Extension, Water Efficiency Technical Assistance Program. Irrigation and Nutrient Management of Young Orchards. Source of Kr = 2 × fc, the 60% canopy threshold, olive and citrus Kc values, wetted-area percentages, the gross-versus-net efficiency step and the walnut shading table.
- Michigan State University Extension. Watering fruit trees with micro-irrigation systems.
- Allen, R.G., Pereira, L.S., Raes, D. and Smith, M. FAO Irrigation and Drainage Paper 56, Crop evapotranspiration: Guidelines for computing crop water requirements (ETc = Kc × ETo). [VERIFY URL]
- California Department of Water Resources. California Irrigation Management Information System (CIMIS).