City taxes shall be due and payable on the first day of July of each year. To all taxes paid after August 31, there shall be added a four per cent penalty, and to all taxes paid after said date, there shall also be added interest at the rate of one-half of one per cent for each month or fraction of a month intervening between valid date and the date of payment, or the first day of March of next succeeding calendar year, whichever date shall first occur. The added penalties and interest herein provided shall belong to the city and shall constitute a charge and shall be a lien against the property to which the taxes themselves apply, collectible in the same manner as the taxes to which they are added.