Sunset Zones: 5 vs 4

bobb_growNovember 11, 2009

I recall reading some time ago a comment on this forum to the effect that there isn't much to distinguish between Sunset zones 4 & 5. As a gardener who is clearly in Zone 4 and who is often a bit jealous of those in Zone 5, I beg to differ. I appreciate the distinction that Sunset makes between the two zones but would go even further and wish that they would nuance their maps a bit more to include some significant pockets of what appear to be Zone 5 climates in the PNW that they include in Zone 4.

One of our favourite activities in winter, especially in February is to visit gardens that clearly are in Zone 5 (e.g. Victoria or Seattle). It is always interesting not only to see how advanced Spring growth is by several weeks in such areas, but also the range of perennials and shrubs that appear to thrive that we usually can't grow in Zone 4 without winter protection (e.g., hebes, lithodora, sometimes even osteospermum etc).

Not only do my observations seem to validate Sunset's distinguishing between the two zones, I think that their editors err by not extending Zone 5 on their map to include sheltered areas such as the slopes south of Bellingham (above Fairview), the coastal area strethcing north and south around LaConner and, in BC, significant sheltered areas of the Gulf Islands and the south east side of Vancouver Island. From my observations, all of those areas seem to have significantly shorter winters than Zone 4 and are able to support Zone 5 type vegetation.

Do my observations seem off the mark to more experienced gardeners/observers?

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Embothrium(USDA 8 Sunset 5 WA)

The climate zoning is sometimes changed between editions. Otherwise, it seems a location can have quite high minimum temperatures and still be mapped Sunset 4 because of the total combination of climate conditions. I remember reading that the main difference between 4 and 5 was how often it got cold.

    Bookmark   November 11, 2009 at 1:44PM
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I would agree! It would be really difficult to capture all the subtleties of Northwest microclimates on a map. There isn't enough long time historical weather data to come up with something really accurate - only in the last couple of years have enough personal weather stations popped up to give us the necessary amount of detail to create such a map. Going by what plants are successful in gardens in certain areas is helpful, and that is probably what Sunset meant to emphasize by designating 4 and 5 as two zones. The limitations though are that some areas in both climate zones remain too sparsely populated to contain a useful number of these indicator plants, and certain winters kill things off at different times in different areas that might on average have approximately the same climate. Then there's always a nebulous grey area between the two zones.

I think your observations are probably quite accurate. The southeast corner of Vancouver Island contains many microclimates that are certainly among the mildest/most favorable in the whole Northwest. So do the Gulf Islands, but there are cold pockets as well, even on the islands.

A lot of the Kitsap Peninsula really belongs in Sunset zone 4. There are a lot of plateaus and elevated frosty valleys especially on the west side of it. The native flora over there is also rather different from on the east side of the sound - it looks much more montane I would say.

    Bookmark   November 11, 2009 at 2:59PM
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Yes, Ian & bboy, I agree with you to a certain extent. Maps are only approximations at best. But, on the other hand, the areas that I happened to mention (and others could mention more) are not only reasonably well populated with many gardeners in that population, but there are at least some weather stations that do substaniate in many cases the distinctions that Sunset uses in its descriptions of the zones (e.g. see

I would also add that Sunset is able to come up with extraordinarily detailed climate zone maps for parts of central & southern California. Some zones appear to be only a mile or two wide in the L.A. area. Yes, the population there is more dense, but in Washington's Puget Sound area & adjacent areas of SW BC, there must be 6 - 7 million people in a reasonably small area.

    Bookmark   November 11, 2009 at 4:03PM
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reg_pnw7(WA 7, sunset 4)

Um, probably not that many people. Seattle is about 1 million. The entire state of WA is about 5 million. The Olympia/Lacey/Tumwater area, at the south end of the Sound, is less than 100,000. My guess for the BC/WA Sound area would be about 2-3 million.

I agree that the distinction between zones 4 and 5 is a useful one, but I don't fret over having extremely detailed mapping of climate zones. "Climate" is a rather insubstantial thing after all, it's someone's estimation of an aggregation of a lot of different factors that vary in time as well as space. All I want from a climate map is an indication of what conditions will generally prevail in an area. I can work out the details of the microclimate of my own site over time.

And as detailed as the Sunset maps of SoCal appear to be to us, people there still complain that they're inaccurate, or not detailed enough. So where does it end?

    Bookmark   November 15, 2009 at 11:42AM
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Embothrium(USDA 8 Sunset 5 WA)

A new whizz-bang-super-accurate-based-on-multiple-data-streams USDA mapping system was supposed to be in the works awhile back. There were even web pages about it on the web site of the Oregon company that was hired to put it together. Later I could not find these pages, somebody posted the Bush administration quashed the upgrade because it would show there had been climate change. Whether that is true or not it is true such a map has still not appeared.

    Bookmark   November 15, 2009 at 2:27PM
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Perhaps I am asking for the impossible. Certainly one could continually demand more detailed climate maps. On the other hand, it still seems to me that the approximately 7 million people who live in the area (about 4.2 million in Washington State counties that border on Puget Sound and at least 3 million in SW BC), large numbers of whom are avid gardeners, could use at least a little more help from somewhat more carefully done climate maps.

Just this afternoon I was talking to Brian Minter, one of BC's best known gardeners, and it became very clear to me that he could use some help in that regard. He knows growing conditions in a 10-15 mile radius of his store but not for the areas further afield from which many of his customers come.

I don't know what one can ask of the editors of Sunset, but they are the ones who developed the zones we are discussing and they certainly sell large numbers of books in this area; I see them on display in virtually every nursery I visit. And, I still think that if this was an area of California with about 7 million people, the maps would be much more detailed.

    Bookmark   November 16, 2009 at 1:26AM
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Since we are referring specifically to Sunset zones here, I think their value is a bit moot. If they were used more widely to designate hardiness zones on specific plants, they might be more helpful but you have to hunt a long time before you find growers or plant wholesalers that actually label plants with Sunset hardiness zones. So interested gardeners would need to tote one or more copies of a Sunset publication around with them when they go plant shopping to cross check the USDA hardiness zone info against the Sunset zone info. And, IME, the zone info contained in Sunset is very much on the conservative end - they exclude all sorts of plants from their zone 5 that do very well in this area.

It also seems to me that most folks who have been gardening for any length of time have a pretty good grasp on the specific microclimates that occur within their gardens.......and these are something that will never show up on any climate/hardiness map. Hardiness zones and climate maps are really only rough guides at best, reflecting what are overall average conditions and what might be expected to thrive/survive within them under similar average conditions. There are always going to be exceptions.

With all due respect, maybe Mr. Minter needs to get out a bit more?

    Bookmark   November 16, 2009 at 10:47AM
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Certainly Sunset spent more time on California than the Northwest... not only on the detail of the climate zones but also in figuring out exactly which plants perform adequately in which ones. But I'm not sure if it necessarily follows that they should provide better coverage for the Northwest, because some agency (publisher, etc.... whatever) in our area might be able to do a much better job of it. It would be exciting to see a Northwest focused counterpart to Sunset's Western Garden Book. As far as climate zones go, I think the zones used in the Timber Press Guide to Gardening in the Pacific Northwest are good as a starting point. Other aspects of that book, such as the coverage of plants, are not of the same caliper as Sunset's Western Garden Book. In fact I really can't think of a Northwest focused book that is. That's unfortunate considering the Northwest else has so much else to be proud of for being unique and being first. A lot of British literature is useful and comprehensive, but those books are often difficult to find, and many gardeners on both sides of the pond will continue to struggle to grasp how different our climates are from each other.

    Bookmark   November 16, 2009 at 7:26PM
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Thanks to all for your comments that cummulatively have begun to convince me. Ian, I appreciate the reference to the Timber Press Guide and will look into it.


    Bookmark   November 16, 2009 at 10:41PM
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Embothrium(USDA 8 Sunset 5 WA)

That book is not very good, don't get too excited.

    Bookmark   November 17, 2009 at 2:18AM
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>>That book is not very good, don't get too excited.

No kidding, they should have saved that title for something else. I finally had a closer look at it, and to me the climate discussion is really the only useful part.

BTW, I'm still waiting for your book to come out.

    Bookmark   November 17, 2009 at 12:22PM
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Embothrium(USDA 8 Sunset 5 WA)

Thanks for the encouragement!

    Bookmark   November 17, 2009 at 2:13PM
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buyorsell888(Zone 8 Portland OR)

I had the pleasure of visiting Mr. Minter's garden a few years ago. I think he is too busy to get out more. ;)

Minter Gardens is well worth the drive from Vancouver. It is lovely.

I haven't looked at Sunset zones in years, is Portland still 6? I'm surprised to see Seattle and SW BC are 4 or 5. I thought we were more similar than that.

    Bookmark   November 19, 2009 at 12:50PM
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Embothrium(USDA 8 Sunset 5 WA)

The Willamette Valley climate is hotter in summer than in most of western WA and SW BC. Sunset 4 is primarily the transition climate between 5 near the shore and 1 in the mountains (of western WA). 6 is supposed to resemble 5 except for hotter summers, although in fact it gets colder than 5 and is not on salt water, might better be considered a continuation of 4 into a hotter summer area.

Seattle is milder than both Portland and Vancouver, because unlike those two cities it is not in the path of a major river that drains cold air out of the interior.

    Bookmark   November 19, 2009 at 9:53PM
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buyorsell888(Zone 8 Portland OR)

Thank you

    Bookmark   November 20, 2009 at 8:37PM
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I know the differences are minor and very localized, but my 1988 edition of the Western Garden Book puts my location (San Juan Island, WA) clearly in zone 5. Now, their web site has definitely in zone 4.

Does anybody know when or why this was changed?

    Bookmark   April 30, 2011 at 3:07PM
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Embothrium(USDA 8 Sunset 5 WA)

Northeasters roar down the Fraser River valley, spilling over Bellingham and the San Juan Islands all the way to Sequim and dropping temperatures 20 degrees in a few hours...

-- 2007 edition, page 36

    Bookmark   May 1, 2011 at 10:48AM
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