Our new normal climate?

April 16, 2013

By Jane Garrison

When the sun comes out during early spring in the Pacific Northwest, we all notice it. In fact, most of us do more than notice it: We go crazy.

Easter weekend provided that moment for us this year. We know the drill: First, we see the forsythia, and then the early flowering cherries and plums, and, of course, the grape hyacinths and daffodils. The star magnolia comes and goes quickly, while the Indian plum blooms prolifically in the woods.

We are shocked when we drive to Mercer Island and see that they are a week ahead of us. West Seattle and Shoreline seem like they have a two-week jump on spring over what we experience here. And yet, all these places, including Issaquah, have the same, new USDA classification, Zone 8b.

It’s amazing what a difference the microclimates make in the timing of flowering, impacting us heavily in the Puget Sound area because of the topography, bodies of water and weather patterns.

Now, the USDA has come to the rescue. It has updated its zone information, and the mapping is truly exciting. Go to www.plant-hardiness.ars.usda.gov, and you will find an interactive map that shows information you might like to know while shopping for plants and planning your yard. In fact, it has apps for iPhones and iPads.

You can find your yard on this map, and locate it by road, topography or satellite view. From the interactive map, you can click on any spot and find out the 30-year average low winter temperature. I did and found that my yard on the plateau averages 16.5 degrees Fahrenheit. Issaquah near Interstate 90 and the lake is higher at 18 F. Along Issaquah-Hobart Road, the average low is 15.9 F to 16.9 F. Low average temperatures in parts of Seattle and on Lake Washington approach 20 F.

Those differences may seem small, but a temperature difference of just 3 degrees can make a two-week difference in bloom time. Be sure to read the verbiage on the website regarding plants and gardens, so you know how to use the information.

I wanted to share this wonderful resource with you, because we certainly can use it as we read more informative tags on the plants at the nurseries. Many tags show the lowest temperature a plant can be expected to tolerate, which helps us more than just the zone number.

Our experience with our own gardens, plus knowledge of exposure, soils and vegetative cover, are still most important. But, with global warming, we may need some help figuring out what the new normal climate really is.


Jane Garrison is a local master gardener and landscape architect who gardens in glacial till on the plateau.


Need help?

Ask questions of master gardeners at the Issaquah Farmers Market starting April 20.

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