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Testing Soil Drainage
On this page find how to measure the rate at which your garden’s soil drains and beneficial ways to change its drainage, including:
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- Understanding soil drainage and how it affects plants.
- What drainage rate is ideal for growing vegetables?
- A step-by-step demonstration of how to measure and interpret results of a soil drainage test.
- What to do about poor or too-fast drainage in garden soils.
A simple percolation test evaluates the texture of your soil. It also measures how quickly or slowly it will drain when saturated with water.
In our simple percolation test, you’ll dig several holes in your planting beds, fill them twice with water, and time how long they take to drain.
The drain rate of your soil depends on the ratio it contains of its mineral components—clays, silts and sand— and how much organic matter it has.
Good drainage—neither too fast nor too slow —is important. Avoid having too-dense soil with your plants standing in water. Prevent their roots from drying out too quickly in overly sandy soil is equally bad. The goal is a happy medium, not too dense and not too loose.
Step-By-Step Instructions
A soil percolation test reveals whether standing water in a garden is due to the soil’s texture—its mineral and organic components—or because of the lay of the land.
When water always stands in a low spot, the only fix is to install drains. When the cause is too much clay in the soil, however, adding organic matter and amendments helps improve drainage and allows vegetables to be grown.
How to Conduct a Simple Soil Percolation Test
To perform a percolation test, dig several holes in your planting beds, 2 ft. (60 cm) deep, and fill them with water. Once that water drains, refill the holes with water and time how long it takes for them to completely drain.
What the Drainage Times Mean
The rate of drainage in typical garden soil, as measured by the falling water level during the test, should be 1–2 in. (25–50 mm) of drop in 15 minutes. Soils that drain near such rates are ideal for growing vegetables, while those that drain slower or faster require amendments or other corrective actions.
Drainage rates slower than 1 in. (25 mm) in 15 minutes suggest that the soil is too heavy with clay or has another condition that might be causing slow drainage. Dig deeper to see if a layer of hardpan or impermeable rock beneath the planting bed prevents water from draining freely.
Drainage rates faster than 2–3 in. (50–75 mm) in 15 minutes also require correction. When the soil drains much more quickly, it is likely that it is porous because it contains too much sand and too little silt and clay.
If soil texture is the cause of a too-slow or too-fast percolation rate, correct either condition by incorporating 2–4 in. (50–100 mm) of organic compost into the top 1 ft. (30 cm) of the soil.