This project is a really neat idea, especially since spring is right around the corner (we can only hope). I found this fun project on The Artful Parent today. All you do is lay out flower petals on contact paper and stick it to a glass window. It looks fantastic! Go check it out on that blog for more images though. It could be a great project to do with your kids, if they have the patience.
When it is actually warm enough for flowers to grow, I might give this a shot!