Sunset Climate Zones

Everyone is familiar with the USDA hardiness zones. But have you heard of the Sunset Climate Zones? Am I the only one who hadn’t heard of this?? How did it take me this long to find out???

The Sunset Climate Zones concept was created by Sunset Magazine. It originally applied to only the western United States, but has since been expanded to cover the entire US. The Sunset Climate Zones, similar to the USDA Hardiness Zones, helps gardeners determine which plants will do well and which plants will do poorly in their area. Unlike the USDA Hardiness Zones, which uses only coldest average temperature to designate zones, Sunset Climate Zones uses hottest temperatures, humidity, rainfall, and length of growing season in addition to coldest temperature to designate different zones. There are 45 Sunset Climate Zones (1-45) as compared to to 26 USDA hardiness zones (1-13, with an “a” and a “b” for each zone). Obviously, the additional features make Sunset Climate Zones more precise than USDA Hardiness Zones. Sounds great, right?

Seattle and Portland, OR are both USDA Hardiness Zone 8b, but are Sunset Zone 5 and 6 respectively. Palo Alto is USDA Hardiness Zone 9b, and is Sunset Zone 15. Practically speaking, what do those numbers mean?

Well….. that part I’m still learning.

Seattle and Portland are the same USDA hardiness zone, but different Sunset Climate Zones. Portland, being more inland than Seattle, had slightly higher highs in the summer and slightly lower lows in the winter, which is good for certain plants that need a bit more chill to have a good fruit set, and like hotter summers.

Okay. Fine. I don’t think there’s all that much difference between Sunset Zone 5 and Sunset Zone 6 to be honest. Microclimates (whether the plants are located in a valley or on a sunny slope or next to a house) probably could be equally influential in happiness of a plant than whether it is planted in zone 5 or zone 6.

I find Sunset Zones more helpful for the Bay Area, however. Palo Alto is zone 9b, but so is Orlando, Florida, and Orlando is very different from Palo Alto. Orlando, FL is hot and humid in the summer with storms; Palo Alto is dry and mild with rarely even a drop of rain for months on end. While a Floridian could probably grow sweet potatoes in zone 9b, we would struggle to get the heat that sweet potatoes like. Accordingly, Palo Alto, in Sunset zone 15, and Central Florida is Sunset Zone 26. That’s more like it.

A little bit about my current Sunset Zone 15 in Palo Alto: Zone 15 is apparently “influenced by marine air approximately 85 percent of the time and by inland air 15 percent of the time.” Plants that do well in zone 15 like moister air, cooler summers and mild (but not tooo mild) winters.

I think, for the Bay Area in particular, Sunset Zones are much more helpful than USDA Hardiness Zones. Here, I have come to learn, lack of heat in the summer can be just a limiting in the garden as cold winter temperatures are. I’d be curious to hear others thoughts on their Sunset or USDA Zones. Do you find the Sunset Zones useful in your area?