September 19, 2016
Mine are growing in a flower bed on the south side of my house in Zone 6b in Wichita, Ks. The clump still blooms but I believe it will soon need to be divided. BTW, it comes back every year and I give it no extra care, such as mulching. It is about 4′ from the foundation.
September 20, 2016
How wonderful your able to winter over your plants.
I would advise dividing in spring and you should not need to divide more than every 5 to 6 years.