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:
- Dig a hole as wide and deep as a shovel head.
- Fill the hole with water and note the time at which the hole is filled.
- Note how long it takes for the water to completely disappear (i.e., 5 minutes, 30 minutes, 1 hour, etc.)
- 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.