There's an old saying, "A giant oak tree is just a little acorn which stood it's ground". Around here hundreds of little acorns stand their ground every year, cast off from our old oak tree. They seem to grow readily, almost like weeds but there's nowhere they like better than landing in one of our $5 planter boxes. We managed to get these from a local farm when they were wanting to get rid of some of them some years ago and they're really great to start seeds in and to give plants a good start.
Here's one little sapling growing amongst some parsley and a good sampling of weeds!