Every potting bench should have a knife or two. A sharpened putty knife may be just the right tool for loosening roots from the outside of a clay pot. An old kitchen knife or pocket knife can also be very useful. Look for a blade that is fairly stiff and 5 or 6 inches long. Do not use a knife from your kitchen...you'll ruin it. Always use care when using knives, do not use them as levers and do not use excessive force. And be sure to sterilize knives between plants when cutting live tissue.