Potassium sulfate was crystallized in a seeded batch cooling crystallizer with no temperature control or natural cooling. Above a critical seed concentration, uni-modal product of grown seeds was obtained even under a natural cooling mode with practically no nucleation. This ideal growth of seed crystals is contrary to the common belief that a natural cooling mode produces small size products with enormous secondary nucleation. The critical seed concentration can be determined easily with data from a laboratory crystallizer on the seed chart, in which the product mean mass size normalized with the seed mean mass size is plotted as a function of seed concentration with seed size as a parameter. A simple and practical method to design a batch crystallizer to be operated with no nucleation has been proposed.