Its rated for zone 7. So you should be fine in zone 8 if its well established. Yes, mulch it well. If you get a few "cold rains" you may want to dig it up so it doesn't rot. Trim, Dry it off and keep it in the crisper drawer of your refridgeratior. Just remember, when it gets too cold it stops growing and has difficulty fending off rot and mold. (It may not return till late spring.)

Okay, there was someone else here from the PNW the other day who said that not ALL of the PNW was subject to rainy climate. Are you? I don't want to jump in here and make a comment that might be offensive to anyone.

If not, cover it with mulch, a good amount, or straw is even better. Dan even suggested constructing one of those tubular containers out of chicken wire and stuffing it with leaves (over the top of the plant).

I covered my A. macrorhiza last year with a PLASTIC BAG of soil - yeah, murder me, okay already. I pulled it off in late spring, and it was a mushy mess. I just cleaned off the mush, part of the top of the tuber popped off revealing the inner pure white beauty of it, and let it dry out, and it came back better than ever this summer, throwing up offsets as it never has before. I have been warned not to do this again. WHY? I might kill it next time.

In Oklahoma, though, we don't usually get as much rainfall or moisture thru snow or sleet or ice, as folks up North do, even in a good year. So I usually don't have to worry as much about leaving mine in the ground.

Susan

Im in zone 8a with extremely rainy winters and they do fine here. In fact, ive left them totally exposed (entire bulb) on top of the ground and they have resprouted. Im in clay soil too btw. I dont think you should have any problem with it overwintering outside.
Michael M.

Thanks for the help.

Oh yeah, totally wet winters. Occasional snow but its wet, no snow pack.

(Dont let anyone know that we have great summers! Tell them the rain here never stops!) Gotta keep up the ruse that it rains all the time here...

I dont want to take any chances cause its a great plant. Anyone know how large these can get in a temperate garden?

Mine have leaves the size of trash can lids after only one year, But I have a very long growing season. Give them a good year to get established, they will grow like weeds after that, and you shouldn't have much problem like raymikematt suggested.

Goody, goody - I can add this to my list for this coming year.

Susan