I didn't plant any Marigolds nor any other outdoors annuals this year.

However, I found a planter box full of thriving Marigolds on my deck when I got home after 5 weeks in Alaska. My guess is that there were dormant seeds in the planter box soil; left over from Summer 2015. Whatever happened, we sure have a nice bumper crop of marigolds now that weren't planted in 2016.