cut them back to the ground in early spring

Cut off any suckers that they might produce

^ Two best answers!!

You can get creative too. Excessive amount of outward spreading can be dug up in clumps to be given to friends and family to plant, or sold at yard sales or local plant sales.

Actually I have been cutting them down to the ground each year. My husband dug so much of it out, and so deeply I was sure he removed it all, but it's still everywhere. Oh well.....

She's a roamer, isn't she! I haven't found cutting to the ground makes any difference to the amount of spreading. I need to dig a bunch of mine out, but I can't make myself do it at this time of year.