Question about Zones

This is a really basic gardening question, but one I've always wondered about.

I have some new beds to plant out, and I want to expand my plant horizons. Several of the plants I'm interested in show they're hardy to Zone 8. Technically I'm in Zone 9, but (most years, anyway) my microclimate in the winter is a little colder than the surrounding areas, and little hotter in the summer.

I don't want to waste my $$ or time or kill any (more) plants just because I like something. Am I taking a huge gamble that if we have a mild winter, the Z8 plants aren't going to have enough dormancy? What other factors besides upper and lower temperatures are involved in determining the zone range for a plant?

Do you have a copy of the Sunset Western Garden book? If so I'd look up your plants in there and see if they'll work in your Sunset zone, that's a much more accurate way to look at things than the USDA zones. If you don't have the WGB, post the names of your plants and I'll look them up for you tonight when I get home if someone doesn't beat me to it.

As far as getting enough cold, if zone 8 is being listed as the lower end of a hardiness range (in other words they say it's for zones 8-10, etc), then you should be fine. If zone 8 is listed as the upper end of a range then you need to do a little more homework--some plants will be listed with zone 8 as an upper limit because they need chill/dormancy in which case maybe you won't have enough chill hours (but maybe you will--we get more chill hours than other parts of the country that are technically in the same zone). In other cases it's because they don't have good tolerance for summer heat in which case you may also be OK (I know we have some stinky heat waves, but for the most part our avg summer temps are lower than places in the south/southeast that are zone 8-9). USDA zones are technically based only on winter low temps so it's not really appropriate to use them for summer heat situations, but many plant tags/books do anyway. Again the Sunset book is a much better guide.

My plants and I both live and die by the Sunset WGB, but when I'm looking at stuff in catalogs or Plantfiles, of course they refer to USDA. I know there was some change recently to the USDA zones, too, which is referred to in some of the mags I get----and frankly that just confused me further.

I guess I should just look at good ol' Sunset---and I have about 5 different versions of WGB, so I may be actually LOOKING at one of my "good ol" WGBs because they have different plants listed in different versions. Of course the other thing that's great about using it is they're not trying to sell me plants.

Thanks for the sanity check!

I don't think the actual USDA zone map has changed (at least yet). The Arbor Day Foundation changed their zones and I know I've heard talk that the USDA is going to change theirs as well, but I don't think they've actually done anything yet. I had looked at the updated Arbor Day zone map a while ago and from what I recall I don't think our area is really affected in the potential zone change so you probably don't need to worry much about that, other parts of the country have changed more than we have.