Garden and Tree Watering Calculators
Work out how much to water flower beds, vegetable gardens, raised beds, potted plants, trees and shrubs, plus how to plan ollas, greywater and rainwater as extra sources. Each calculator answers one question, shows its formula, and works in US or metric units.
Which garden calculator do you need?
Find your question below. Each calculator does one job, so picking the right one gets you a precise answer.
| Your question | Use this calculator | How it works |
|---|---|---|
| How much water do my flower or mixed beds need this week, after rain? | Garden Watering Calculator | Bed area and plant water-use class, minus rainfall. |
| How much water does my vegetable garden need, crop by crop? | Vegetable Garden Water Calculator | Crop list and growth stage set weekly water per crop. |
| How much water does my raised bed need to get properly wet? | Raised Bed Watering Calculator | Bed dimensions and soil depth set gallons and frequency. |
| How much water do my potted plants need? | Container Plant Watering Calculator | Pot size plus a drainage fraction set water per watering. |
| How much water does my tree need? | Tree Watering Calculator | Trunk diameter or canopy area and ET set gallons per watering and week. |
| How much water does my shrub need? | Shrub Watering Calculator | Canopy size and plant factor set weekly gallons. |
| How many ollas do I need, and how often do I refill them? | Olla Watering Calculator | Bed area and olla size set the count and refill schedule. |
| How much greywater can I reuse for irrigation, and how far will it go? | Greywater Irrigation Calculator | Occupants and fixture flows set daily greywater and the area it can serve. |
| How much rainwater can I harvest for irrigation, and what tank size do I need? | Rainwater Irrigation Supply Calculator | Roof area, rainfall and runoff coefficient set monthly harvest and tank size. |
All garden and tree calculators
Beds, vegetables and containers
- Garden Watering CalculatorWeekly water for flower and mixed beds, after rain
- Vegetable Garden Water CalculatorWeekly water per crop, by row or bed
- Raised Bed Watering CalculatorGallons to wet the bed, plus a drip layout
- Container Plant Watering CalculatorWater per watering for pots, by size and drainage
Trees and shrubs
Garden and tree watering basics
What university extension research says, in brief. Each calculator page goes into detail and cites its sources.
About 1 inch a week for vegetables
University of Minnesota Extension gives about 1 inch of water a week as a starting point for vegetable gardens, watered twice a week on sandy soil and once a week on heavier, moisture-holding soil. It notes 1 inch over 100 square feet is about 62 gallons.
About 10 gallons per inch of trunk
Colorado State University Extension recommends 1 to 2 inches of water every two weeks for established trees during the growing season, which works out to roughly 10 gallons per inch of trunk diameter. Newly planted trees need more frequent watering while roots establish.
Pots need a bit of extra water to drain
Nursery best management practices from the Southern Nursery Association, cited by the Alabama Cooperative Extension System, call for a leaching fraction of about 15 to 20 percent: some water should run out the drainage hole with every watering to flush excess salts.
Ollas can cut watering by roughly half
University of Arizona Cooperative Extension reports that olla irrigation may save 60 to 70 percent of water compared with a watering can, since water moves straight from the buried clay pot to the root zone. It notes research on ideal olla spacing is still limited.
Greywater and rainwater systems are also governed by local plumbing, health and water-rights rules, which always come first over any number here. For related data, see the crop coefficient table and the soil infiltration rate chart.
Related calculator categories
- Scheduling and ET calculatorsEvapotranspiration, water requirements and irrigation timing
- Soil calculatorsWater holding capacity, infiltration and soil texture
- Drip irrigation calculatorsEmitters, tubing and run times for beds and trees
- Lawn watering calculatorsHow much and how long to water turf
- Cost and savings calculatorsWhat your garden watering and conversions cost
- All calculatorsEvery irrigation calculator by category
Sources and review
This page and its calculators are reviewed by Daniel Reeves, PE, CID. Last reviewed . See our methodology and editorial policy, or report an error.
- University of Minnesota Extension. Watering the vegetable garden.
- Colorado State University Extension, Tri River Area. Watering Trees.
- Alabama Cooperative Extension System (ANR-2706). Auditing Overhead Irrigation Systems in Container Nurseries: Leaching Fraction.
- University of Arizona Cooperative Extension. Irrigating with Ollas.