Prior to the completion of farmers’ market facilities to be financed with proceeds of bonds, any portion of the principal proceeds derived from the sale of the bonds which the commissioner may determine is not then needed for any of the purposes for which the bonds are authorized to be issued shall be invested by the State Treasurer in permitted investments which mature at such time or times as the department shall direct. At any time, and from time to time on order of the commissioner, any such investments may be sold or otherwise converted by the State Treasurer into cash.