Do you ever look at an empty lot, or a sad old, forgotten municipal or commercial landscaping and think about scattering some flower seeds? Or something edible? If it grows, somebody could appreciate it.
These things so often occur on impulse, so couldn't be discussed first, but if there was a support-group post for those who are considering something like propagating some trees for a park that really needs some shade, or throwing some seeds in an empty pot at a gas station or neglected municipal flower bed, tomato or watermelon seeds in an empty lot, we could trade ideas and provide encouragement.
I'm sure we all realize that things like this are subject to the whims and maintenance jobs of other people, and the weather, so one should always approach these things with the assumption that nothing will come of it, but if it works, it was worth a try.
I am not suggesting anyone do anything unethical or illegal, such as trespassing, only positive things, aiming for whatever infinitesimal increase in the world's plant biomass. Random acts of anonymous social kindness and beautification. If you have an opportunity to DO what you would like to see, maybe you will be more likely to take action on the opportunity after reading this, and what will hopefully be encouraging additions and ideas to follow. If one wishes their neighbor had more flowers, or tomato plants, scoffing at their weeds or over-abundance of grass won't help as much as giving the neighbor some flowers or tomato plants, should one be so fortunate and blessed as to be able. Our world can only be as beautiful and productive as the efforts made by any of us.