Good question! I think they're completely dormant in the winter so don't do much of anything. I think the only reason fall planting is deemed better than spring planting is that dividing the roots is pretty traumatic and dividing when they're going dormant is safer than dividing when they're starting to grow for the year. Transplanting 3-5 eye divisions in the spring is no more risky in my experience than in the fall; they just typically won't bloom that year. I've ordered from Gilbert Wild and Hollingsworth for spring delivery before and those peonies did just as well as fall planted ones.
