I love doing this, I spread plants all over the yard from one small plant that someone will give me. I have several plants that seeded themselves from last year including cilantro, lettuce, snapdragons, morning glorys, and petunas to name a few. I also have poenies that are at least 70 years old...they were may grandmas...I bought her house years ago and when I moved I dug them up and planted them hereposted by Oatmeal:
One thing that you can do though if you grow plants that you have to pull, is to constantly sow new seeds so that you always have new friends Or better yet, make cuttings of the original plant - this way they will all be clones of the mother plant!!