Weed Laws of Montgomery County
 
The "weed laws of Montgomery County, allow people to plant almost
anything non-noxious that can be considered beneficial or ornamental (note
that any native plant or grass can be argued to be excluded from the
definition of "generalized growth" and so be allowed anywhere on ones
property).   You also have to make the case that none of your plants are
endangering public health or safety - which is not hard since no "public"
should be on your property. Make the case also that natural landscaping
favors predators of rodents (owls, hawks, fox etc) where as a manicured
landscape provides no cover or habitat for rodent predators  and so it is
that kind of landscape instead which encourages rats. Native Impations or
Jewel flower can be considered an ornamental and is certainly beneficial. 

      All the information below is taken directly from the Montgomery
County Code which can be found on-line by going to the Montgomery County
(and Montgomery County Council) web site:

From Chapter 58 of Montgomery County Code
Note this section from 58-3 and Part III amendment M to 58-1(** are
added for emphasis)

  "An owner, lessee, agent, and any other person in charge of land in
  a subdivision or within 100 feet of a subdivision must not allow:     (a)The
  generalized growth of any weed*; and     (b)Any**generalized plant growth
  **more than 12 inches high within 15 feet of any property boundary. **Not
  included within this definition are trees, ornamental shrubbery, flowers,
  garden vegetables, compost piles, or any plant certified and listed by the
  director of the department of environmental protection when used for soil
  stabilization purposes." 

   **(kmm note - NATIVE GRASSES, SHRUBS, TREES  AND PERENNIALS
     should be exampt from the "generalized growth" definition as well - both
     ornamental (since beauty is in the eye of the beholder and AS PART OF A
     NATURAL HABITAT OR GARDEN)

     *Weed: Poison ivy; ragweed; kudzu; Canada, musk, nodding, plumeless,
     and bull thistles; any plant, except another thistle, identified as a
     noxious weed under State law; and any other plant which the Director finds
     by regulation endangers public health or safety, if allowed to grow
     unchecked. (Mont. Co. Code 1965, § 116-1; 1972 L.M.C., ch. 3, § 1; 1972
     L.M.C., ch. 16, § 5; 1977, L.M.C., ch. 40, § 1; 1989 L.M.C., ch. 21, § 1;
     1996 L.M.C., ch. 13, § 1.)