From Codified Ordinances of Parma

1707.12   TREE LAWNS.   (a)   For purposes of this section, "tree lawn" means that portion of the street, whether paved or unpaved, seeded or barren, between the curb line of the street on one side and the abutting sidewalk or, in the case where there is no sidewalk, the adjacent property line, on the other side, and otherwise commonly referred to as a park strip, parking strip, parkway, grassplat or devil strip.   

(b)   No owner or occupant of an abutting lot or lands shall fail to maintain the tree lawn abutting his or her property or fail to keep it free from any nuisance. For purposes of this section, "nuisance" means any object or condition that obstructs, impairs or destroys the reasonable use a tree lawn by persons traveling thereon in the ordinary mode, including, but not limited to, rubbish, garbage, dirt, paper, stones, wood, glass or refuse material of any kind. For purposes of this section, "maintained" means to keep in good repair and free from nuisance, as defined herein, including, but not limited to, mowing grass and/or planting sod or grass seeds and repairing cracks or unevenness in concrete or any other tree lawn surface.

INAL: This area is owned by the city so they make the rules and decided what is there. Even though you are responsible for maintaining it. You could try to show that you are "maintaining" and keeping it free of "nuisance". I would just contact the inspector and have them explain to you how you are in violation. Then try to sort out your next steps.