Clematis Volunteer

This is our best Clematis and it was a volunteer many years ago.  We planted some Mums in a large pot and they did well for a couple of years.  All the sudden this Clematis popped up and it has done great since then.  This year it is 8 feet tall with a bunch of blooms.  One interesting characteristic of this plant is the way the blooms face the ground instead of pointing sideways or toward the sky.