Soil Drainage

Plants we purchase generally indicate the ideal or preferred soil drainage conditions. Whether perennials, shrubs or trees the plant may require average, good or excellent drainage to perform at its best. Sometimes we see that a plant will tolerate poor drainage or clay, or dry sandy conditions. So how do we know if our soil drains well?

Naturally there are some guidelines to determine whether our garden or landscape soil is suitable for certain plants. Most often plants require “average drainage so we need to understand what that means as well as determine our soil’s rate of drainage. Plants that require average drainage needs soil that drains about 2 inches per hour. If your soil drains slower than 1 inch per hour it is important to either amend your soil or select plants that tolerate or thrive in wet soil. If your soil drains 3 or 4 inches per hour or more it drains fast and again, will require soil amendments to hold moisture or select plants tolerant of dry soil.

Now to conduct a simple soil drainage test. Dig a hole one foot wide and one foot deep. Dig those dimensions as closely as possible in order to properly determine inches per hour. Fill the hole with water and let it completely drain. Fill the hole again and make note of the time. Keep a close eye on the hole and note how long it takes to drain.

Evaluate your results with the guidelines below:

• 0 to 4 minutes: Fast draining soil

• 5-15 minutes: Good draining soil, may be prone to drought

• 10-30 minutes: Ideal or average draining soil

• 16-60 minutes: Average to slow draining soil

• 3-4 hours or more: Poorly draining soil with either a high clay content or an impermeable mineral (hardpan) below.

Drainage is determined by the texture of your soil - sand, loam or clay. Once you understand the texture and determine the drainage, you can either select plants appropriately, or amend your soil. Check out the articles about soil amendments and feeding your soil with compost and amendments.