You do know that Sunset has an entirely separate zonal system from the USDA? And have always had such? Typically most of the Puget Sound area - USDA zones 7&8 - are Sunset zone 4 or 5.

While the Sunset zones tend to be much more fine-tuned than the USDA ones - 24+ compared to the 13 now listed by USDA - they are really only applicable to reference with the Sunset Western Garden book, as I know of only one large grower (Monrovia) that ever lists them on the plant tags or in the catalog. I agree, it is rather confounding -- although I agree that sometimes a more detailed hardiness evaluation like Sunset's (which takes in rainfall, altitude, summer heat, etc. in addition to winter cold temps) may be helpful in making plant choices, if no one follows the same guidelines, what's the point??

Also IME, Sunset seems to be overly conservative in their ratings. According to them, we shouldn't be able to grow a ton of stuff that grows here without worry :-)

Um ... 'creating their own zone parameters' was done decades ago. It ain't new.

I find the USDA zones to be pretty much useless except when communicating with gardeners on non-regional forums and even then they're pretty 'confounding'. Seattle zone 8 is nothing like any other zone 8 in the country. When I worked in the hort industry in California we ONLY used Sunset zones - USDA zones are pretty meaningless there. They only deal with winter hardiness - not an issue in places that barely see frost.

What strikes me as bizarre, personally, is insisting on using the USDA zones when they're only meant for limited use in determining winter hardiness. The Sunset zones are much more inclusive of year-round growing conditions.

The new USDA hardiness zones have more behind them than before. Still not climate zones, though.

Sunset created their own zones decades ago. They have nothing to do with the USDA zones. They take heat and rainfall into account not just frost.

I like the Sunset zones. When a plant label tells me it's perennial in USDA zones 4-7 I always assume it'll do fine in my USDA zone 8 garden, and when the label says USDA zones 8-10, I will probably avoid it, so how is that useful? But if the Sunset gardening book or Monrovia website tell me that it'll do well in Sunset 5, that's information that means something to me.

Commerical sources indicate the wrong USDA zones for plants all the time. Few involved in preparing descriptions seem to understand that 0-10F, 10-20F etc. is the AVERAGE low temperatue for each zone, and not the lowest low temperature. A plant hardy to only 15F will not last for a long time here in USDA 8, where many sites get below 15F fairly often. When in doubt, assume a plant is one zone less hardy than indicated on a nursery label etc.

Interesting points. I had no idea Sunset had established their own zoning and that it has been around so long. I usually find multiple standards redundant or at odds with one another. But there's hardly an industry where multiple standards don't exist, so I shouldn't get my panties in a twist. And as some of you have said, you find it helpful. Personally, I still find it odd. To my knowledge there aren't any growers that apply Sunset's zoning standards to their labels. Anyone can look up specific hardiness points per plant, but zoning and labeling were created to make it easier for the consumer.