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?

3 thoughts on “Sunset Climate Zones”

  1. Never heard of this zoning system, but I expect it makes a lot of sense esp. in the warmer zones you mentioned. As climate change progresses, Sunset zones will be useful in more areas. For example, here in New England, our winters are getting milder and summers hotter, which is stressing maple trees that need COLD winters. They are predicting the loss of these trees in the not-too-distant future. A huge blow.

    1. Yikes! I didn’t realize maple trees were endangered. It’s crazy to think that *maple trees* (a staple of our landscape) could be relegated to climate controlled conservatories to preserve the species like panda bears in a zoo. If I learn anything from 2020 – between the pandemic, political climate, and the forest fires – it will be not to be so complacent. We had been warned about a pandemic, but and didn’t do anything to prepare until it was too late. We’ve had even more warnings about climate change…. Given our track record, I don’t have much hope for the maple trees.
      That’s really depressing. I’ll still do what I can! Maple trees are one more thing to consider when I think about turning up the thermostat, using single use cups or cutlery, or taking a plane flight (not that I do much of the latter these days). And further incentive to continue eating a vegetarian diet!

      1. Thank you, Marie. If everyone did their part, we could still mitigate some of the change, so kudos to you. I often liken it to trying to turn the Titanic… we’re running out of time as the iceberg looms.

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