Soil Drainage in Containers: Debunking a Myth

Soil Drainage in Containers: Debunking a Myth

By Michael Jenkins

At Gardzen we strive to provide reliable and accurate information in this blog, and that occasionally means debunking a gardening myth even if we used to believe it ourselves. Like many gardeners around the world, we were taught that we should put gravel or a similar material in the bottom of flower pots and containers to ensure good drainage. As it turns out, adding gravel to containers does not help drainage and ensuring good drainage and root aeration in container plants is a bit more complicated. So, let’s dig in, debunk a myth, and learn about his one together as we learn the reality of soil drainage in containers.

Gravel in Plant Containers: Myth and Reality

It seems simple and obvious: a layer of gravel or other relatively small, hard material to the bottom of a container so that the water can more easily flow out of it should the soil become saturated. It stands to reason that water would flow through gravel more easily than through soil—and it does! The issue arises with a 150 year old discovery: water doesn’t flow very well from a dense material into a less dense material. The dense material—in this case the soil—acts like a sponge and traps the water, preventing it from moving through the soil. So, while most of us were taught to put gravel in the bottom of containers to help soil drain, the reality is that it doesn’t work very well.

Adding insult unto injury, it turns out that adding gravel can potentially make things more difficult for our plants. As our fellow gardening educators at Parker County Master Gardener Association demonstrate in this beautiful illustration, adding a layer of gravel can keep water trapped in the soil near the roots of the plants, which keeps the soil around the roots waterlogged and may cause root rot and lead to poor health or even the death of the plant in question. So it’s best to avoid using gravel inside of flower pots or other containers for drainage and explore other solutions.

But what are the alternatives? Let’s take a look . . .

Ensuring Good Drainage in Garden Containers

As it turns out there are other, better ways to ensure good drainage and good root aeration, both of which are necessary for the health of our plants. Let’s take a quick look at some of these approaches to container plant drainage so that we can make educated decisions about which one works best for us:

  • Using a good potting soil or container soil mix is an important step in ensuring good drainage. Container soils need to be rich in organic materials while still being loose enough to allow air movement and water flow. By using the right mix and giving it the right care, you’ll help prevent drainage issues in your container plants.
  • Holes in the bottom of containers work—but there’s a catch! Plastic and terra cotta containers generally have holes in the bottom to help with drainage, but in order to work properly those holes have to be clear and open. This is where gravel comes in—a layer of gravel underneath the containers in a tray or saucer can help with air and water flow from the holes in the container and thus mitigate or prevent drainage issues.

  • Fabric containers or terra cotta containers help drainage by providing an air-permeable or porous later that air and water can move through. Both types of containers help ensure drainage but should generally be kept out of puddles or pooling water in order to do so. Fabric containers can also support root health by preventing root binding and similar issues, further enhancing the health of our plants.

  • Watering our plants appropriately is a final step in ensuring good drainage—water won’t need to drain if there’s not too much in there in the first place! Different plants and different climates or weather conditions will necessitate different watering practices, so a little research is necessary to get this right.

 This has been our favorite type of blog to write—one in which we get to learn something ourselves and expand our own gardening knowledge while sharing it with you. We hope it helps you address drainage in your own container plants and plan for the future. Gardening is a process of continual learning, and we’re glad to have you along with us!

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