You also may find them growing in places no where near where you planted them.
I bought one little plant about 6 years ago, and now have well over 30 good size plants sprouting everywhere.
I give them away all the time.
I live in the woods so I don't care where they show up.
Some sprout those long stems with tiny pink flowers - which I assume is where the seeds are and are carried to other areas by bees and wind.