Plant Roots and Water Follow the 40-30-20-10 Rule

Q. Please explain the 40-30-20-10 rule when watering. Why is it important? There are lots of different ways to water plants.

Doesnt matter how deep the roots are, all roots generally use water following the 40-30-20-10 rule. Divide the roots into four equal parts. The top fourth of the roots uses 40% of the water, the second quarter uses 30%, 20% and 10% follow suit. Drawing citation lost.

A. Most plants use water stored in the soil following the 40-30-20-10 rule. Divide the roots of plants into four equal parts. If it is a large tree and its roots are three feet deep, divide this three feet into four equal parts (nine inches for each part). If one-foot-tall plant roots are one foot deep, divide the roots into four equal parts (3 inches for each part).

After a heavy rain or a full irrigation, plant roots start using the water stored in the top quarter (25%) first. When this top layer starts getting used, then the plant begins using the second (25 to 50%) layer of stored water, then the third and finally the fourth. When the plant finishes using water stored in the soil, it uses this water following a 40% (top)-30%-20%-10% (bottom) rule. Plant roots, just like the top, grow when they use water. This is one reason plant roots grow deeper when they are watered deeper.