Testing Your Soil Drainage Is Easier Than You Think

Posted on: 28 January 2015

If you are like most gardeners, you've probably read a lot of plant descriptions and noticed that almost all plants need loose, well-drained soil. You may be wondering exactly how you determine if your soil is well-drained. You may have even assumed that if you water your plants and water runs through the bottom of the pot quickly that it means the soil is well drained and you have nothing to worry about. This isn't necessarily true. Let's take a look at exactly what the term means and how you can tell how well the drainage of your soil is.

What is well-drained soil?

Well-drained soil is defined as soil that allows water to filter through it relatively quickly without pooling in the soil, explains the University of Missouri Extension. This means that rainwater or supplemental water moistens all areas of the soil and the excess water drains away from the plants. In containers and pots, this means the water collects in a saucer beneath the pot or runs off through the holes in the bottom of the container. While the soil becomes moist, it does become soggy or waterlogged. 

Soil in Pots and Containers

It's easy to be fooled by soil in plant pots and containers. If the soil becomes overly dry it tends to pull away from the sides of the container. When this happens, watering your plants results in water running through the bottom the pot without moistening the soil. This should not be mistaken for well-drained soil. In this case, you will need to thoroughly moisten the soil before you can determine if it is well drained.

  • Submerge the entire plant pot or container in a bucket of barrel of water. You will notice air bubbles escaping from the soil, as the water works its way into the air pockets in the soil. This is normal and means your soil is absorbing water. 
  • Allow it to soak for 20 to 30 minutes, or until all bubbles stop.
  • Remove the pot from the water and allow it to drain naturally.
  • Water the plant again when the soil feels dry about an inch below the surface.
  • Well drained soil in pots and containers should drain within a few minutes when you water them. If the water runs through the pot almost immediately, it means your soil drains too quickly. If it takes more than a few minutes for the water to drain, you soil may have drainage problems. Check the drainage holes or change the soil.

Testing Garden Soil for Drainage

Determining how well your garden soil drains may seem more challenging, but there is a simple test you can perform with nothing more than a garden shovel, ruler and a bucket of water.

  1. Dig a 12-inch by 12-inch hole to a depth of 12 inches in the soil.
  2. Fill the hole with water and allow it to drain. This prepares the soil for the drainage test.
  3. Fill the hole again and record the amount of time it takes for the water to drain into the soil.

According to the National Gardening Association, soil that drains in 10 to 30 minutes is ideal for gardening. If it drains in less than 10 minutes, the soil is likely sandy and drains too quickly for all but drought tolerant plants. If it takes hours to drain, the soil is not considered well-drained and will likely become waterlogged after rains. Soil that remains wet chokes out the oxygen to the roots of plants and promotes disease and root rot.

Final Thoughts

Add organic matter, such as peat moss, compost or well-rotted manure to the soil to improve both aeration and drainage. Ironically, it works with soil that drains too quickly as well as soil that drains slowly. It improves the moisture-holding capacity that quick draining soils need and increases the size of the pores between soil particles allowing water to drain through slow draining soils. Organic matter also provides slow-release nutrients to the soil.


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