When you venture out to the garden shed to begin potting flowers and plants for the season, finding flower pots stuck together may stop your planting progress immediately. Terra cotta flower pots are especially prone to sticking together when you stack them into towers for storage. Try several methods to unstick flower pots, using utmost care to avoid breaking or chipping the flower pots.
Place the pots on their sides on the ground and cover the pots with the thick towel to prevent breakage. Gently tap on the sides of the pots with the rubber mallet. Do not use extreme force with the mallet---gentle taps are all you should use to unstick the pots. Roll the pots around as you tap to try to loosen the inner pot from the outer pot.
Set the stuck pots into the freezer for approximately 15 minutes. Terracotta contracts as it gets cold, so exposing the pots to cold temperatures may contract them enough to allow you to separate them. Do not leave the pots in the freezer for longer than this time; however, because the pots may crack if they freeze completely.
Cover the drainage hole of the inner pot temporarily. Use a piece of duct tape to cover the hole or insert something into the hole to plug it. Fill the inner pot with ice water and then set the outer pot in a sink of hot water. The temperature difference between the inner pot and the outer pot should cause the inner pot to contract and the outer pot to expand, which will unstick the pots.