Sunset zones and USDA zones are different.

Frankly, the Sunset zones are much more detailed and accurate and take heat into account rather than just frost but the USDA zones are nationwide and more well known outside of the West.

And one rarely finds growers that tag their plants with anything BUT the USDA hardiness info - even Monrovia, the largest plant grower/wholesaler in the country and based in California adheres only to the USDA zones. So if you follow the Sunset zonal info, that means you have to haul around your trusty copy of the Western Garden Book to crosscheck the suitability of any potential plant purchases. And Sunset also tends to be overly conservative in their hardiness ratings as well.

So when I look at plant tags that say hardy to zone 6 or 7, does that work for me? Is it better to stick with things that will be fine for zone 5? I'm still confused on this. I didn't know there were 2 different zone guides. That's not nice to do to beginners!

Eileen

IMO, if you live in the Puget Sound basin or the areas immediately surrounding the Sound (between the Olympics and the Cascades) just forget about the Sunset zones :-) They are unnecessarily confusing since few plant tags ever refer to them and there is very little distinction in the overall growing climate in this area. Closer to the water will be milder and may have more beneficial microclimates and higher into the foothills will make the climate a slight bit more extreme but not enough to make a huge impact.

So go with your USDA zone, which is 8. You are pretty safe selecting anything with a hardiness zone of 7 or below. Those plants listed with a hardiness zone of 8 may prove to be a bit marginal and how well they do may be more of a trial and error process until you get the feel for your specific garden conditions. However, you will read many posts by gardeners in this area that grow plants that are not supposed to be reliably hardy here but nonetheless thrive for years.

FWIW, USDA zone 8 is considered to be a very mild climate zone and encompasses a huge range of plants - the vast majority of plants you will encounter at area nurseries will be more than suitable for growing in this area so you are not very limited by hardiness factors.