I have a spot I've been working on finding perennials/self seeding flowers that will naturalize. It's a tough spot, a hillside of heavy clay with basically full sun in summer and little rain. These plants also have to hold their own against tall grass. Eventually I want a meadow effect.
Here are my top performers so far:
1) Comfrey (Symphytum officinale) - The comfrey is holding its own and the flowers are pretty. These are seed bearing, and I hope they do spread.
2) Common/Tall Evening Primrose: I grew a few from seed, then scattered the seeds from those plants on the hillside and forgot about it. They popped up this spring and are now about 4' tall. I am impressed!
3)Roses. I hadn't realized how tough these plants are.
4) Lavender. Would be nice if it was taller, but I am impressed with how tough these are.
5) Just planted a Velvet Centaurea and that thing is taking off like it's in nice fertile loam. It got eaten down by slugs and is coming back strong.
Any other "kick @ss and terraform new planets" flowering plants out there? List em if you got em!