How to Do a Soil Drainage Perc Test

A soil percolation test (perc test) measures how fast water drains through soil. It's a short, direct test that costs nothing but a half-hour and a stick. In gardening, a perc test tells you whether a planting site will support plants that need well-drained soil, whether a rain garden will function.

A soil percolation test (perc test) measures how fast water drains through soil. It's a short, direct test that costs nothing but a half-hour and a stick. In gardening, a perc test tells you whether a planting site will support plants that need well-drained soil, whether a rain garden will function correctly, or whether a bed needs drainage correction before planting.

In my Melville yard, the sandy loam drains so fast it sometimes creates problems — moisture-loving plants dry out between waterings. Perc tests have confirmed drainage rates that informed which plants work where on the property without guessing.

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Two Types of Perc Tests

There are two versions of the perc test, used for different purposes:

1. Saturated hydraulic conductivity (garden perc test): Used to evaluate drainage for planting beds, rain gardens, and general landscape drainage. This is the version most gardeners need.

2. Standard septic perc test: A regulated engineering test for sizing septic systems or leach fields. It follows specific protocols established by state health departments and must be conducted by a licensed professional in most jurisdictions. This guide does not cover the septic test.

The garden perc test described here follows the method outlined by Penn State Extension and NC State Extension.

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