Mulch can cut a bed's watering by around half.
As recorded: A layer of organic mulch over the soil cuts the water a bed loses from its surface, and with it the watering the bed needs, by around half in Colorado State's figure.
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
Mulch covers and shades the soil, so less of its water evaporates from the surface and the moisture below stays more even.
What to do about it
Spread 2 to 3 inches of a coarse organic mulch, such as straw or bark, over the soil between the plants. Grass clippings go no deeper than 1 inch.
How much it matters: 'reducing irrigation need by around 50%' (CSU GardenNotes #715), a general figure with no conditions attached; NMSU and UMN give none. Shown as 'around half', never as a computed saving.
The evidence
Evidence: checked against 3 sources in the research-based literature.
The 3 sources
In general, mulching minimizes evaporation of water from the soil surface, reducing irrigation need by around 50%.
Natural organic mulches and white plastic mulch applied in the summer will tend to cool soils.
Studies show that mulch reduces evaporation from the soil surface and helps soil hold water.
Where this rule stops
Around half is Colorado State's general figure; the saving in your bed depends on the mulch, the soil and the weather. Organic mulch also tends to keep the soil cooler in summer.
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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.
- A person read the sources and confirmed it
- Added to the rules
Cite this page
Milpa Gardens. "Mulch can cut a bed's watering by around half." Evidence grade: Promising. https://milpa.garden/rules/layer-organic-mulch-over-soil-cuts-water/
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- The rule names its mechanism and is settled, by sources a person has read and checked or by plain arithmetic and geometry.
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