Avocado (Persea americana) trees thrive outdoors in U.S. Department of Agriculture plant hardiness zones 9B to 11, but the lush green leaves of the plant will add an exotic tropical note to your décor if it is too cold to grow them outdoors in your area. The key to keeping an indoor avocado plant healthy lies in its roots. Overwatering rots its roots, wilting the leaves. Since this is often a sign of thirst, your first instinct may be to keep watering, but this will only make the problem worse.
Fill the bottom of a large pot with 1 inch or so of gravel. Make sure that the pot has adequate drainage holes and a drip tray to catch runoff.
Mix together equal amounts of potting soil, peat and perlite, and fill the pot about one-third full with the soil mixture. Do not pack the soil mixture down because avocados prefer looser soil.
Spread newspaper over your work area. Remove your avocado plant from its present pot and gently shake off as much of the soaked soil as you can.
Dry the roots very gently by squeezing them carefully with paper towels. Do not pull or tug on the roots.
Place the avocado in the new soil, making sure that the roots are spread out and not kinked up or bent.
Fill the pot loosely with the rest of your soil mixture.
Water the avocado thoroughly, wetting the soil. Let the water drain through and empty what is in the drip tray as soon as the runoff stops. Soak the soil once per week or so, when it starts to appear dry. Empty the drip tray each time.