Take an empty planter, upend it and look at the holes at the bottom. They may not seem very important, but they determine what happens every time you water. If your container doesn’t have an exit route for excess moisture, the plant roots will be saturated for too long. You may see normal potting on the top of the container, but at the root ball the potting may be soggy. Plant roots need water, but they also need air to be healthy. In a planter without drainage holes, the air spaces of the potting are filled with water. Roots in waterlogged soil can become stressed, showing their displeasure with leaf discoloration, weak growth, or other symptoms. A novice might see these signs and water, believing the soil is too dry. It isn’t; the soil was too wet before you watered.
Drainage holes also show you how the water is distributed within your container. When you slowly water with a watering can, after all the watering, a small amount of water may drain out the bottom. You don’t have to water your container enough every time to flood the saucer, but at least some water should drain at the end of the watering. If the water drains immediately, your potting mix may have pulled away from the sides of the container, or it may be so loose that the water hasn’t soaked in evenly. If nothing drains and your container is still very wet days after watering, something isn’t right.
Test the container with a little potting mix before the plant is installed. Water it gently, and see how it behaves. Does the potting mix absorb the water, or does the water stay on the surface? Does it drain out the bottom after a few minutes? Does the saucer stay full of water afterwards? A saucer protects surfaces from water leaks, but don’t let the planter saucer become a pond under the plant. Dump the excess water out of the saucer after the container has drained, especially for plants that don’t like to be in soggy soil.
The size and type of the container can change how fast or how slow your soil dries. A small container in the hot afternoon sun may require you to monitor the moisture of your container more than if it was a large container in a more lightly shaded spot. A plastic container will hold more moisture than an earthenware container that allows water to evaporate through the walls. Mulch on top slows evaporation, too, but the soil underneath could be too dry, too wet, or somewhere in between. Don’t water from the top. Before you rewater, test the soil from the top down with your finger.
Some planters are sold without drainage holes as decorative pots. These are supposed to have an unglazed nursery pot nested inside them. The plant’s container should drain, but you need to see what’s going on with your planter after watering. Take the inner container out and see if water is in the bottom of the decorative container. If the roots have risen above the water line, you may be safe. If the bottom of the inner container is soaking, the decorative container may look good, but your plant will be dealing with the exact same symptoms as if the decorative container had no drainage holes at all.
A proper planter won’t take all the guesswork out of growing your plant, but at least it allows you to make the right decision. By monitoring your container with a well-draining container, good potting mix, and regular testing of the soil, you can tell when your plant is getting enough. If the next time you visit your plant’s container, take a peek at the saucer, the leaves may not tell you all the details. But what’s happening on the bottom?