Soil Percolation Rates

Percolation is the movement of water through the soil. Measuring the percolation rate will help determine if the soil drains fast enough where you want to: direct water with a downspout, create a swale or use retention grading.

The percolation rate will also help determine how suitable the soil is for certain trees. Some need well-drained soil while others prefer a water-logged site.

Use the method below to measure soil percolation rates:

  1. Dig a hole as wide and deep as a shovel head.
  2. Fill the hole with water and note the time at which the hole is filled.
  3. Note how long it takes for the water to completely disappear (i.e., 5 minutes, 30 minutes, 1 hour, etc.)
  4. If the water is draining slowly, note how much water is draining each 30 minutes (i.e., 1/2 inch every 30 minutes).

Assess your results:

  • 0–4 minutes: You have fast-draining soil. This area is fine for a swale or retention grading. However, plants will need to be watered often unless they are drought tolerant.
  • 5–15 minutes: Soil drainage is good. This area is ideal for a swale or retention grading.
  • 16–60 minutes: If soil is draining at least 1/2 inch per hour (for swales) or 1 inch per hour (for retention grading) the soil is fine.
  • Several hours/days: Very few trees will do well in this soil. If you want to install a swale or detention basin, replace the soil with 2 feet of gravel at the bottom and 6 inches of loam soil (a soil mixture of sand, silt and clay) on top. This will allow water to sink in instead of pooling on top.