A quality commercial potting soil created for container gardening should have all the right ingredients for proper drainage. If your soil or container is not providing adequate drainage, plants can have "wet feet," that is, the roots being exposed to too much water. Constantly wet roots may lead to disease or even plant death.
Check your container for proper drainage holes. In some plastic and synthetic containers, holes may need to be added, or they may be present but need to be punched out or screwed open.
Make sure drainage holes are not obstructed by large root masses or some outside obtrusion. Hold the plant by the crown-- the base of the plant closest to the soil line-- and wiggle the pot loose from the plant to observe root growth. If the roots are pot-bound and form the shape of the pot, repot the plant in a larger container with new soil.
Shake the plant lightly, holding the crown to remove excess potting soil from roots and set plant gently aside.
Add new or additional drainage holes by driving a large nail into the bottom of the plastic or synthetic pots with a hammer and removing the nail. A masonry drill can be used to add drainage to concrete or stone containers. Terra cotta is too brittle and will break if you try to add holes.
Mix perlite or vermiculite, porous materials that improve drainage by keeping soil from clumping up, into your potting soil. It should make up about 10 percent of the mix. Many good-quality commercial potting soils have perlite or vermiculite already in their ingredients, but you may want to add more.
Mix an equal amount of compost into your potting soil. Commercial and homegrown composts may contain manure, composted leaves and bark and other materials high in nutrients but that are also lightweight in consistency.
Replant plants back in container with new soil mixture.