Adding a layer of gravel to improve drainage in pots and containers is a persistent myth that I believed for many years. People think that a layer of gravel in the bottom of pots will help with drainage and keep the soil from spilling out. We’ve always done it, so it must be right.
However, through my decades of gardening and horticulture, I’ve learned that this widely accepted technique is actually counterproductive. In this article, I’ll explain why this particular garden myth is false and provide better alternatives for your potted plants. Here’s what you need to know about using gravel in potted plants.
Why Gravel Doesn’t Improve Drainage
This gardening myth is based on a mistaken idea that putting gravel in potted plants will increase drainage. Below, I’ll debunk this.
- Gravel vs. soil: Gravel does drain water — obviously, water runs through gravel faster than soil. The opposite is also true: soil holds water better than gravel. Stick with me here.
- Soil acts like a sponge: Water won’t run out into the gravel, out of the pot, or anywhere until the soil is saturated. If you don’t believe me, try laying a sponge on top of a pile of gravel, then pour water into the sponge. Does the gravel make the sponge drain faster? No, the sponge fills up, and it won’t drip until it can’t hold another drop.
- Space decreases: Just like with a sponge, water naturally settles toward the bottom of the soil. But because you’ve partially filled your pot with gravel, that soggy soil bottom is now higher (and closer to your plant’s roots). Basically, it’s like having a smaller pot.
- Poor results: So, you end up with an unhappy, crowded plant sitting in overly wet soil, and you’ve wasted valuable pot space with gravel that’s not helping.
The Science Behind Soil Water Movement
Understanding how water moves through soil is crucial to debunking the gravel myth. Soil particles create a network of tiny pores that hold water through capillary action. This means that water doesn’t simply flow straight down through the soil.
Instead, it moves laterally and upwards as well, creating a moisture gradient. When you add a layer of gravel at the bottom of a pot, you’re actually raising the water table closer to your plant’s roots, decreasing the amount of space. This can lead to overwatering issues.
You may be worried about soil washing out of the bottom of your pot. In most cases, drainage holes are small enough that this isn’t a problem. However, you can always put a paper coffee filter, a piece of screen, or a shard of pottery over the holes before adding dirt.
Drainage Is Simple if You Use Quality Soil
Your plants will be happier if you uniformly increase the drainage of the soil itself. Choose high-quality potting soil that drains well. And if your plants need even more drainage, instead of putting gravel in the bottom of your pot, try mixing perlite or organic matter into your potting soil to increase drainage throughout the pot.
How To Use Gravel With Potted Plants
If you want to put gravel to work with your potted plants, use it outside the pot. Put a layer of gravel in your plant’s drainage tray or down inside a decorative planter, then sit your plant pot on top. The gravel will hold water and increase humidity while keeping your plant’s roots up out of the puddle.
Gravel in Non-Draining Pots
The best type of flower pot has good drainage holes in the bottom of the container, and you should always shop for pots that drain. But for large pots that don’t have holes, some people put gravel in the bottom of the pot, which creates a sort of internal drainage tray to collect water under the dirt. Some people are able to get this to work, but it can cause problems, including:
You can’t see the gravel, so how do you know how much water is down there? If excess water builds up, the soil will turn into a soggy mess, and your houseplant will be on the fast track to root rot.
Water, nutrients, and air move through the soil using capillary action, sort of like a straw. If you plug the bottom of a straw, it stops working, and when you plug up the bottom of your plant’s soil (by trapping it in a non-draining planting container), it stops working, too.
If you’ve ever opened a container that’s been in your refrigerator too long, you’ve learned firsthand what happens when moisture and organic material are trapped in a space with no airflow. The same can happen with your plants: a moldy mess.
Alternative Methods for Improving Drainage
Instead of relying on gravel, there are more effective ways to enhance drainage in your potted plants. One method is to choose a high-quality potting mix that’s specifically formulated for container gardening. These mixes often contain materials like perlite or vermiculite that improve aeration and drainage.
Another option is to select pots with multiple drainage holes or to drill additional holes in existing containers. For plants that require excellent drainage, consider using fabric pots or air-pruning containers that allow for better air circulation around the roots while still letting water drain and maintaining soil saturation.
Final Note on Gravel in Pots and Containers
Putting gravel or a layer of rocks at the bottom of your plants’ pots and containers can actually hinder proper drainage and root development. Instead, use on using well-draining potting mixes and appropriate containers, and employ proper watering techniques. Your plants will be healthier and more vibrant than ever before.
Further Reading
- Flower Containers for Beginners (article)
Frequently Asked Questions
No, contrary to popular belief, adding gravel doesn’t improve drainage and can actually raise the water table in the pot, potentially harming your plants.
Use a piece of landscape fabric, a coffee filter, or a small piece of broken pottery (pot shards) over the drain holes to prevent soil loss. A good garden soil or other high-quality growing medium works best.
Yes, you can use decorative rocks as a top dressing, but don’t put them at the bottom of the pot as it doesn’t improve drainage.
