You can divide the plant in spring or Bears Breeches is easily propogated by root cuttings done between November and February when the plants dormant, just clear the soil around the roots and find pieces of root around pencil thickness insert 2-3 inch pieces in gritty compost so the tops around 1inch below soil surface, cover with grit and wait for them to sprout, you must make sure the cuttings are the right way up though the top being the end nearest the parent plant as they won't root upside down, good luck :-)

Thank you Simbad - if I had known that a few years ago, I could have had a few more of this wonderful plant. Hopefully will get some root cuttings going before we move (not sold yet, though). Cannot split the plant as there is only one with two flower spikes!! Can I put the root cuttings in an unheated greenhouse over winter?

Yes Wendiam unheated greenhouse is perfect, may be springtime before you notice new growth, good luck with selling your house :-)