At the time and place fixed for such hearing the board of county commissioners shall determine whether such weed district shall be created and if such board determines that such district shall be created, it shall fix the boundaries thereof, but shall not modify the purposes of the petition with respect to the weed or weeds to be destroyed, prevented and exterminated as set forth in this petition, and shall not enlarge the boundaries of the proposed district, or enlarge or change the boundary or boundaries of any district or districts already formed without first giving notice to all land owners interested as provided in RCW 17.04.030. If the board shall determine that the weed district petitioned for shall be created it shall pass a resolution to that effect and shall assign a number to such weed district which shall be the lowest number not already taken or adopted by a weed district in such county, and thereafter such district shall be known as "Weed District No. . . . . of . . . . . . County," inserting in the first blank the number of the district and in the second the name of the county in which the district is organized.