Measuring Garden Slope: String Level and Simple Math
Measuring garden slope needs only stakes, string plus a line level. Extension guides express slope as rise over run.
The short answer
The UW Arboretum sheet runs a level string from an uphill stake to a downhill stake 10 feet away. Measure the drop at the downhill stake. Divide rise by run then multiply by 100 for percent slope. Iowa State says slopes under 5 percent need few special steps.
How do you measure slope with a string?
The UW Arboretum sheet uses two stakes, string, a line level plus a ruler. Hold the string at the base of the uphill stake. Run it 10 feet, or 120 inches, to the downhill stake. Slide the string until the level reads true. Measure from string to ground at the downhill stake. That is the rise.
| Option | What it does | Source |
|---|---|---|
| 10 foot string | Sets the run | Measuring slope (RGS 2 5) |
| Line level | Levels the string | Measuring slope (RGS 2 5) |
| Ruler | Reads the rise | Measuring slope (RGS 2 5) |
How do you figure percent slope?
The UW Arboretum formula is rise divided by run times 100. Iowa State also gives slope as a ratio. A rise of one foot over 12 feet is 1:12 or 8.33 percent. Mississippi State says a rise of two feet over ten feet is twenty percent.
Rise over run: times 100. 1:12: 8.33 percent. 2 in 10: twenty percent.
What does slope mean for garden beds?
Iowa State says slopes of 8 to 16 percent need special planting steps. Slopes of 20 percent or more are steep. Run rows perpendicular to the slope along the contour to slow water. Terraces use cut plus fill to break a long slope into steps, says Mississippi State.
Under 5 percent: few changes. Contour rows: slow runoff. Terraces: shorter steps.
Troubleshooting
String sags: loose line. Tighten it before reading.
Soil washes down rows: rows run downhill. Turn them across the slope.
Mulch slides: smooth mulch. Use coarse shredded bark.
Kind Seed Co shares these plant notes for growers of all kinds. For more on site planning see garden microclimates for cannabis and mulch for cannabis. Read planning an outdoor cannabis garden layout for layout. See raised beds for cannabis for bed building.
Sources
- Measuring slope (RGS 2-5), University of Wisconsin Arboretum
- Gardening on slopes and hillsides, Iowa State University Extension and Outreach
- Gardening on steep slopes, Mississippi State University Extension
FAQ
When is a garden slope steep?
Iowa State plus Mississippi State call slopes of 20 percent or more steep.
What tools do you need to measure slope?
The UW Arboretum sheet uses two stakes, string, a line level plus a ruler.
Do terraces help on a slope?
Mississippi State says terraces break a long slope into shorter steps. It suggests walls only a foot or two high for home builds.
Which way should rows run on a slope?
Iowa State says run rows perpendicular to the slope. Planting along contour lines slows water flow.
What slope is too steep to mow?
Iowa State says slopes of about 30 percent or more are too steep to mow.
