Drainage for Containers

Many instructions on how to plant a container garden begin by telling you to add a layer of course material to the bottom of the container to improve the drainage. Often recommended are sand, gravel, or pottery shards. But does this really work?

According to Washington State University horticulturist Linda Chalker-Scott, in her book The Informed Gardener, these "solutions" can actually make the drainage in your pots worse. (The articles in this book are also available online here.) Because water moves through coarse materials faster than through soil, it seems intuitive that adding a coarse material would improve the water movement through the container. Unfortunately, water "does not move easily from layers of finely textured materials to layers of more coarsely textured material" (p. 82). In fact, the water will not move between the layers until the soil is saturated, meaning that the soil may actually stay wetter than if there were no coarse material in the bottom at all.

Using the same material throughout the container will provide the best drainage for a container with holes in the bottom. If you are concerned about your potting media falling out of the the bottom of the container, it can be lined with a layer of newspaper or landscape fabric.

1 comment:

  1. I'm so glad I'm catching up today and read this! I'm getting ready to start a container garden- it's in an old plastic bassinet thingy (hard to explain) and my husband was saying I should put a layer of rock on the bottom. I wasn't going to then started wondering-- after reading your post I'm just sticking with the dirt. He already drilled holes for me so I'll be set. Thanks!

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