The county commission shall provide for the manner in which the regulations, restrictions and boundaries of the districts shall be determined, established and enforced, and from time to time amended, supplemented or changed. In order to avail itself of the powers conferred by the provisions of sections 64.211 to 64.295, the county commission shall request the county planning board to recommend the boundaries of the various original districts and appropriate regulations to be enforced therein. The board shall make a preliminary report and a proposed zoning order and shall hold public hearings thereon and shall afford persons interested an opportunity to be heard. A public hearing shall be held in each township affected by the terms of the proposed order, notice of which shall be given in the same manner as provided in section 64.231. The notice shall state the time and place of the hearing and the place where copies of the proposed report and order will be accessible for examination by interested parties. The hearings may be adjourned from time to time. Within ninety days after the final adjournment of the hearings the board shall make a report and submit a proposed order to the county commission. The county commission may enact the order with or without change or may refer it back to the board for further consideration. In the preparation of its report and proposed zoning order the board may incur such expenditures as are authorized by the county commission.