You can get the zone from a local neary nursery. You could also contact nearby universities with agriculture departments as well as your county Agriculture Extension Service Office.

If you are in Walla Walla (and I assume from your username you are), then you are in USDA zone 5b/Sunset zone 3b. The USDA zone will probably be more meaningful for you as that is the way the majority of plants are coded for hardiness. The Sunset zones tend to be much more regional in nature and take factors other than just average winter cold temps into consideration. Many who garden in the NW use both :-)

If you want to go through the effort of removing and recovering your shrubs daily, you certainly can. But there is also no compelling need to do so. Generally you'd want to wait until after the last hard frost for your area (March 27) to uncover completely. Often the greatest cold damage to hydrangeas occurs from late spring frosts that hit after the plants have begun to emerge from dormancy. You don't want to rush the season :-)

I keep my hydrangeas covered until April 15th. They have no problems staying in the dark for that long. Within no time at all after that they start to leaf out. How did you cover yours? Burlap only?

gardengal.. thanks for the response. I also ran into a zone map (but cant remember who it was) that said that the USDA zone map hasnt been updated in a while. They said they are suppose to do it every 20 yrs or something like that and they havent done it. Yes it is a higher risk when they start thinking it is spring and then it turns cold. I didnt cover them last year and we had a chill in early March. THought I had lost the blooms. I did get some but thought I might get more if I protected them.

hydrangeasnohio.. yes I just wrapped them in burlap and tied it with some hemp loosely. And your right I am sure that they will catch right up. I guess you could say I am just getting cabin fever and wanting to get out there in the garden LOL