The hole in the bottom of a plant pot provides drainage to the soil above. Most pots have small holes that allow water to drain out while keeping the soil in place. However, some clay pots and plastic planters have large holes in the center of the pot. Soil can slip through the holes, along with the water, making a mess each time you irrigate your plants. Multiple methods exist to plug the hole without compromising drainage in the pot.
Place a piece of broken clay over the hole before filling the pot with soil. The clay blocks the hole so soil can't escape, but moisture can still work around the clay piece and drain from the pot.
Line the bottom of the pot with a piece of wire or plastic screen material. The material holds the soil but doesn't inhibit water movement. Screen material works especially well in pots with multiple holes requiring plugging.
Line the pot with a coffee filter before adding soil and planting. The coffee filter works the same as the screen material, but it breaks down over time so the holes aren't permanently blocked.
Insert a cork into the drainage hole if you need a watertight seal, such as for a container water garden. Seal around the cork with plumber's putty. The cork and putty make a watertight seal but are easily removable if you need the pot for traditional planting later.