Lisa,

Yes, I grow Gooseneck Loostrife. I'm well aware of its spreading abilities, so I planted it in clay soil, that often dries out. Since Silver Maple trees grow nearby, the roots are in stiff competition, and it spreads slowly, enough that I can manage it by dividing. I would not plant it in moist soil, that could spell trouble (invasiveness).

Julie

Like Julie's mine also is pretty slow to spread. I have it in two spots in my yard, both under trees. When I first moved into my house the only two plants growing in my yard were snow on the mountain and Lysimachia punctata, which is the yellow loosestrife. Still trying to get rid of the snow on the mountain, but after three years of contantly digging out roots I finally got rid of the yellow loosestrife. The gooseneck loofestrife doesn't have roots anything like the highly invasive variety.
Jen