The method of producing monocrystalline or multicrystalline blanks, especially silicon blanks, by using a vertical-gradient-freeze method, includes providing a crucible with a rectangular or square-shaped cross section and a heating jacket disposed around the crucible, which has a number of flat heating elements with a meandering course disposed on side faces of the crucible. The heating jacket generates an inhomogeneous temperature profile corresponding to a temperature gradient in the center of the crucible. The flat heating elements preferably comprise parallel heating webs, whose heat output is set by varying the conductor cross section. To avoid local overheating in corner areas of the crucible, constrictions of the cross section are provided at inversion zones of the meandering courses of the webs. The flat heating elements can be formed from a plurality of interconnected individual segments.