Zone 15, accurately, are the maritime valleys. They get their climate influence primarily by the fact that marine air has free access inland a bit. Santa Maria (within the SM Valley) and Lompoc (within the Lompoc Valley) are good examples of SWGB Zone 15.

SLO only has some pockets that come close to this kind of climate. Most of SLO, "slopes" or not, are considered Zone 16.

The eastern ends and valleys of SLO (such as near Edna) start slipping into Zone 14 territory.

The winter temp differences between 15 and 16 aren't really that great but it will impact at least 10% of the plants you may consider. If you suspect that you might be borderline, go with the more extreme zone and choose plants that are pretty much guaranteed.

By the way, what edition of the SWGB do you have? The latest addition changed quite a bit of the zone maps.

Joe

Thank you for clarifiying that for me. Zone 16 just made so much more sense than 15 based on temps, but the zones seemed to follow the topography. Your local examples really helped. Zone 16 it is! My SWGB edition is definitely older, but I have checked on the Sunset website for the current maps.

Sunset does leave a few of us out here and there. : ) My zip puts me in a 10 but I don't have the summer heat of the general high desert area and my winter temps are colder. So I am closer to the 3 that they give a local mountain community. The problem is most of my small town spreads out to the desert floor while a smaller portion, where I'm located, is at a higher elevation, 2-3 thousand feet for some of us. I've learned to go with the minimum low temp and moisture requirements, and forget the zone.

Consider your microclimate as well. Technically I'm in Zone 21 (occasional ocean influence, valleys) but I own a half acre hill, which acts as a mini-zone 20 (cold air basin) or maybe even 18. As others have pointed out, we're all better off choosing the plants that will perform across a wide variety of zones (I know that if it's 14-24, it's almost guaranteed to be happy).

Much as I love the SWGB, have they split up the zone 17 in the latest edition (I haven't bought it yet)? Always bugs me that they lump the Oakland hills where I live, with places that have very different weather. We're on the edge of the SF fog belt, so it's windy and only a few degrees warmer than downtown SF. My tomatoes sulk and my roses get terrible rust, LOL!

Buy the book. It's easier to see the maps.

If you can't afford the book, check your local library.

Can afford Internet access but can't afford the book?

Free internet access can also be had at the library. You sign up for an hour at a time to use their computers. Also, some of us are either unemployed or on limited incomes, and must make choices about where to spend our money. We've decided to pay $19.95/mo. for internet access, and borrow books when we can.

And I always like to plug the library. It's a wonderful but underused resource that your tax dollars are paying for. The LA Central Library downtown has a marvelous collection of books on gardening in two different sections, literally hundreds of books. If you can take the subway, it's an inexpensive way to entertain yourself. Or, you can go to a local branch and do an inter-library loan, and save the cost of a subway ticket.

Thanks for letting me go off topic for a few sentences.

I could see about making a kml file for GoogleEarth on ArcGis. Now who wants to sacrifice all the map pages from one of their books? The online maps don't have resolution anywhere what I need for that.

Ryan

I am on 2.5 acres up in the Santa Cruz mts where the climate varies from end to the other end of my property so I put down Sunset 14-17 because they all apply.