Soil Composition Analysis
Drainage 24 Hour Test
Garden Tip
TB1473
Technical Bulletin Series
Drainage Test - Discovering soil percolation
Almost every garden instruction guide refers to the importance of "well-draining soil." If water drains (percolates) away from plant roots too quickly, the plants will parch even if they're getting regular water.

And if water doesn't drain, many plants will drown and rot from the roots up. Another complication from "wet soil" is due to low oxygen availability, the roots do not function properly. Yellowing leaves are often one of the symptoms.

A percolation test - or perc test - is a great way to measure drainage
in your lawn or garden soil. Here's how to conduct an easy, DIY soil perk test in your yard.

Note: In order to determine the percolation rate of a soil separate from other parameters such as: Hydrostatic water pressure and Absorption, this test requires the allowance of 24 hours for the soil to completely saturate with water BEFORE performing the timed drainage rate test.

If for some reason you do not have that much time to make this important determination of soil drainage rate, please refer to Garden Tip TB1468 subsection section (Jar Test). Here Planting Guru has factored these other parameters (Hydrostatic Pressure, Absorption, Effective Capacity and Water Holding) into the Conventional percolation rate, derived from this test in order to determine soil type within about an hour.

Step 1: Dig a Hole at least 12" in diameter by 12" deep, with reasonably straight sides. If you're testing your entire property, dig several holes scattered around your yard, since drainage can vary.

Step 2: Fill Hole with Water, and keep the hole wet for 24 hours. This provides the time necessary to completely saturate the soil leaving only the "Percolation Factor" to evaluate.


Step 3: Then let it drain at least 6 inches in order
to allow drain rate measurements to be taken.



Step 4: Measure Drainage time. Measure the time it has taken for water line to drop for each inch it drains. After 3 to 4 measurements you will have enough data. If it has drained more (or less) than an inch when making the next measurement, then record the time it was measured and the level of the water line.

If the drainage rate is less than 1/4th inch per hour, this indicates poor drainage and many plants will have trouble growing in this soil without utilizing a technique like "Berming" (there are others) to improve drainage.

If the drainage rate is faster than 5 to 6 inches per hour, this indicates excessively fast drainage. Most plants will like to suffer drought and wilting in this kind of soil, or the amount and frequency of irrigation water applied will be very high. In this event techniques like layering the bottom and surrounding several inches of soil in the planting hole with an amendment like "Peat Moss" can help hold the water for the plant's root system. Generally large shrubs and trees will not be practical in this type of soil.


Ideal drainage varies according to the types of plants to be located there. Vegetables require really good drainage. Some shrubs and trees are more tolerant of wet soils than others. Knowing your percolation rate AND the type of plant can be key to recognizing and resolving plant stress issues.


The Table above indicatres the drainage rate ranges for the 12 basic soil composition categories. The drainage rate itself is the primary partameter that will determine which irrigation flow rate to utilize in order to efficiently match the soil being irrigated.

The "Happy Zone" for most plants will be a drain time between 1/4th inch per hour and 5 to 6 inches per hour (24 Hour Drain Test- only). Faster drainage rates often create drought issues for many plants, while slower rates create respiration issues. Before planting, there are a number of things to do to improve oxygen access to the roots, or help to keep the soil moist longer.

To help understand the importance of Irrigation and Soil Matching, please see TB-1116.