Suturing a partially cracked pot will prevent it from breaking completely.
Bind the empty pot around its circumference with lengths of twine at both top and bottom. Using an 1/8-inch masonry bit, drill a pair of holes, one to either side of the crack, each about 1/2 inch away from the crack. Create additional pairs of holes as necessary, 3 to 4 inches apart.
Slip a 4-inch length of 20-gauge brass or copper wire through each pair of holes from the outside, twist wire tight, and smooth it flat against the inside of pot. Remove twine, and refill pot.