Soil Composition
One Hour Drainage "Quick Test"
Garden Tip
Technical Bulletin Series
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: For ultimate accuracy the soil being tested should be completely saturated before testing for drainage. Articles from various Universities will discuss keeping the test hole wet for 24 hours before testing, and will report percolation rates of about 1 inch per hour as a good drain rate. The intent is to discover soil percolation independent of other soil properties like hydrostatic water pressure and absorption. Most people don't have that much time for this process. Also in practice we do not irrigate our plants when the soil is already saturated. So, here I will report data related to approximately a one hour wait between tests.

Because the soil does not saturate within this short of a time this "Quick" percolation rate will be faster. What really matters though is that the test identifies the type of soil correctly. This "Quick Test" will get very close to accurately identifying soil type.
Technical Data for Quick Testing
Math and Science

Parameters affecting and creating this difference in drainage rates include: Hydrostatic tension between wet and dry soil, the Soil's ability to hold or absorb water and the effective field capacity of the soil. Simply put, the percolation reading after only one hour of waiting are quite different from those after allowing 24 hours for the soil to saturate. Still, these readings when compared to the chart provide very useful information regarding the composition and drainage characteristics of your soil.

By taking the Percolation rates for Sand, Silt and Clay and then determining the weighted average for each soil type (based on a typical percent profile) a Soil Composition Factor [SCF] can be established: SCF = ((PR1 + PR2 + PR3) / 3). At this point we bring in Soil Porosity "SP" (the percent of water when completely saturated) as well as Water Holding Capacity "WH" (water holding capacity, inches per foot). To arrive at a calculated Time to Drain "TD" From these we can use the formula: TD = (WH * (SCF2 / SP)) See the chart below for results from the application of these formulas.

These factors have already been worked into the Algorithms of the Garden Calculator Pro-I, and the "Drain Times" reported there are from this accelerated method. If you use the traditional method for a Drain Test and fully saturate the soil first the Garden Calculator Pro-I provides an alternative chart for cross-referencing drainage rates to identify Soil Type.
Steps for Doing the Test
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 let it drain completely. This should take about an hour and pre-moisturizes the soil. This helps give a more accurate test reading.

Step 3: Refill Hole with Water about an hour after it first drained.

Step 4: Measure Drainage time. If the hole takes 1.5 hours or more to empty this second time, drainage is not good. If possible check drainage every 10 minutes. Measure the water level by laying a stick, pipe, or other straight edge across the top of the hole, then use a tape measure or yardstick to determine the water level. Continue to measure the water level every hour until the hole is empty, noting the number of inches the water level drops per hour.

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 "Happy Zone" for most plants will be a drain time between 25 and 65 minutes (for Quick Test). 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.