It is unlawful to permit the growth of noxious weeds, bushes and heavy undergrowth, which exceed 10 inches in height. All such weeds, bushes and heavy undergrowth are a public nuisance and shall be pulled, cut, and destroyed at least twice a year, once on or before May 1, June 1, August 1, or whenever the grass has reached the height of 10 inches, whichever occurs first.