Vegetables need about an inch of water a week
Vegetables need about an inch of water a week, and what the rain doesn't bring, you do.
As recorded: A growing vegetable garden needs about an inch of water a week (25 mm), rain and watering counted together. In a month whose normal rain falls short of that, an open bed's watering makes up the difference, and where the rain falls below a quarter of it, nearly every drop is yours.
Promising A person has checked it against its sources. If you skip this, it still grows, just less well. The planner suggests it.
How it works
Growing plants draw water out of the soil, and sun and air dry it from the top. What the rain does not put back, the soil loses until it is watered.
What to do about it
Read the month's normal rain beside the inch a week to see how much of it is yours, and let the soil pick the day: water when it is dry at the second knuckle, and water long enough to reach the roots. An inch over a 4 by 8 foot bed is about 20 gallons, and over a square meter about 25 liters.
How much it matters: About 1 inch (25 mm) a week while the crop grows (UMN, Arizona). A bed's week is that depth over its area: UMN's '62 gallons for a 10x10-foot area' and 'About 20 gallons for a 4x8-foot raised bed' are 0.62 gallons a square foot, and 1 mm over a square meter is 1 liter. A month's yardstick is the week times the month's days over 7.
The evidence
Evidence: checked against 4 sources in the research-based literature.
The 4 sources
The average vegetable garden needs about 1 inch of rain per week. This looks like: 62 gallons for a 10x10-foot area. About 20 gallons for a 4x8-foot raised bed.
While growing, vegetable crops need about an inch of water per week in the form of rainwater, irrigation water, or both
One inch of rainfall per week is adequate.
Most vegetable gardens require approximately one inch of water per week, excluding rainfall.
Where this rule stops
It reads each month's normal rainfall, so it cannot see this week's weather, and a month's rain can come in one storm and run off. NC State words the inch as 'excluding rainfall', though it also says to pause watering in rainy weeks; this follows UMN and Arizona, which count the rain toward it.
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How this rule has changed
Every change is dated, newest first. The full record, with each reason, is in the data download.
- Details updated
- A person read the sources and confirmed it
- Added to the rules
Cite this page
Milpa Gardens. "Vegetables need about an inch of water a week, and what the rain doesn't bring, you do." Evidence grade: Promising. https://milpa.garden/rules/growing-vegetable-garden-needs-about-inch-water/
A garden planner built on graded evidence. Every claim states its evidence grade and links its sources on the page. Cite it with the grade, and add the date you read it.
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How we grade evidence
- Well established
- The rule names its mechanism and is settled, by sources a person has read and checked or by plain arithmetic and geometry.
- Promising
- The mechanism is named and the literature backs it. A few questions are still open.
- A good hunch
- Plausible by its mechanism, but field studies are thin, so treat it as a lean.
- Contested
- The evidence points both ways, or no study has tested it, so the planner does not enforce it.
- Refuted
- The claim did not survive its sources. It is kept so the folklore can be answered.