I came across an article the other day about Guerrilla Gardening and making seed bombs. If you are not familiar with the term, it is basically gardening in spots where you don't have permission to do so by using a ball of seeds and compost-able materials. I sort of did it at my workplace, although I did get permission, so it really wasn't guerrilla gardening. Behind the office was a small plot of land which was bare when I got here. I bought a flat of impatiens and planted them one weekend. I had planted wildflower seeds, but they were coming up looking like weeds and I was getting comments about it, so I went and bought the flat. As you may be able to see here, I put a sign up that seeds were planted so that the landlord would not weed the spot.
seed bomb article make me chuckle, especially the part where they make the clay ones were made in the form of a gun or a grenade. I imagine that could cause some issues in places where people could panic. I love the idea of planting flowers and things where there is just dirt which just collects trash.
Another article that I saw was on an British website and they referred to it as nature's graffiti which really made me chuckle. The pictures they showed on that site though were bulbs, which probably took a little more time than throwing a seed bomb and hoping it will rain enough to spread the seed around. Whatever the method, the idea of spreading around plants and flowers in vacant lots really appeals to me.