next to my back yard is what is called common ground. there's trees, bushes, plants. and under the trees and next to the shrubs are growing weeds. I'm unable to pull them out so i'd like to spray weed killer. is there one that won't harm the other greenery, trees,bushes and so on.

Most, if not all, sprays would be harmful in some way to some other plant or to the ground itself. Better not to risk it. If it is 'common ground' I would hesitate to spray anything unless and until each and every other person agrees.

May I ask why one cannot pull the weeds adjacent to their own property? It seems the safest thing to do. Is there someone or some agency that needs to grant approval?

I forgot to ask...
what city/state/country are you in?