Proper pot size it vital for houseplant health. Pots that are too small dry out more quickly, provide improper soil aeration, and can cause plants to lift themselves out of the pots as they become root bound. Overly large pots require more fertilizer and water. Pot size depends on the plant, as some plants prefer smaller pots while others require larger pots. Many plants also gain in size the larger their pot is, so large pots may lead to an over-large plant that is difficult to tend.
Remove the plant from the existing pot. Place your hand over the top of the pot, allowing the plant stem to pass between your fingers. Turn the pot upside down into your hand, and lightly thump the bottom until the plant slides out.
Inspect the roots to determine if repotting is even necessary before purchasing a new pot. If there are many roots near the top of the root ball or if the roots completely wind around the soil mass, the plant needs repotting.
Use a pot that is one size larger in diameter than the existing pot. For example, if the plant is in an 8-inch pot, upsize to a 10-inch pot.
Increase the depth of the pot by 2 inches for most plants. If the plant is badly pot-bound, increase the depth of the pot by as much as 4 inches to give the existing roots more room to spread. Roots are primarily grown into the bottom of the pot, so increased pot depth is more necessary than pot width.
Plant succulents, cacti and other shallow-rooted plants into wide, shallow pots. Use pots that are 2 to 3 inches wider in diameter than the plant and about half as deep. Shallow-rooted plants do not require lots of soil depth in order to thrive.