New Interactive USDA Plant Hardiness Zone Maps
Posted by: Kate Bryant on Jan 26, 2012 at 10:44AM
5 Comments
Nearly four years in the making, the new USDA Plant Hardiness Zone Map (now known as the PHZM) is finally ready.
This map was reformulated by experts – many from Oregon – in the fields of weather, geography, mapping and horticulture.
Horticultural experts have been complaining for years that the old USDA map (where, for instance, the entire Portland area, with all its topographical differences, mapped out in the same zone) was inaccurate. Not only was it outdated (didn’t take recent climate change into account) but it also failed to account for the many variations within each state and region of the country. It also was not searchable.
The new map is based on detailed GIS mapping work, and is searchable by zip code, so higher elevation areas in East Portland and in the West Hills map out with different zones than, say, inner Southeast Portland, where I live – which now maps out at Zone 9A (with average winter lows of 20-25F).
The interactive map is fun: from here, enter your zip code, then click on the map and find the hardiness zone throughout your neighborhood by clicking on any point on the map.
Learn more about the differences between the new map and the old ones, as well as information about maps, climate, and plant hardiness here.
I like Plant Delights Nursery owner Tony Avent’s suggestion that the new map is likely to be of use for prospective home buyers. What home-buying plant nerd wouldn’t want to have the opportunity to live in a little banana belt where semi-hardy plants might better overwinter?
While the technology isn’t sophisticated enough yet to account for micro-level differences due to, say, the tall building behind your house that blocks light in your garden all winter or the reflected heat from your neighbor’s RV pad, it does factor in larger geographical features such as the river and significant elevation changes.
So visit the site and see how your zone has changed. Is the map easy to use? Does it more accurately reflect the reality of your garden? Let us know!
I would love for the USDA to put out a map with the average coldest temperatures for a 10 year period rather than just one year. This map smooths out the averages and doesn’t take into account the coldest temperatures over time. This would be more helpful to gardeners.
Yes, I like knowing the average but it would be more helpful to have information on the highest highs and lowest lows readily at hand. Especially for gardeners – like so many of us in Portland – who are adventurous in our plantings… I wonder if there’s a way that info could be layered, so you could toggle quickly between the two systems of categorization? Surely if anyone could pull strings, it would be you Paul!
I’m curious to know how nurseries (such as Paul’s wholesale outfit, Xera Plants) will handle the segue from old plant labels (with old hardiness zones) to the new. The transition could be dicey. Will plant nurseries and the public really take to the new system? How to tell which system the numbers on the tags refer to? Time will tell!
Great point Tony makes about using the map when your relocating. Moving from another state I had no idea when we bought this place in 2005 that we chose a cold spot!
This new map is a lie.I live in zone 4 in which Marchal Foch grape will not grow.It grows well in zone 5.I tried & it froze to the ground 3 years in the row.According to new map should grow because now I have zone 5.Brave New Lie.
Loree, due to a dip in topography, I too live in a cold microclimate, but within a warm “banana belt”. Winter lows are higher just a few blocks away from here! Which brings me to the issue Stan raises… there are microclimates within each zone (there are several in my small neighborhood) and they are not accounted for in any existing system I’m aware of. We must assess our microclimates before planting. Hardiness maps do not “lie,” they just present information based on a particular data set. In this case, the information used to recalculate the zones reflects warmer conditions. Paul points out that it would be more helpful to gardeners if extreme lows were accounted for better. I agree, and note that someone who takes the map literally could get in trouble. I’m interested to see how plant references (on line and in books), as well as plant nurseries, will go about re-zoning all the plants they describe or carry in stock. Seems like a big chore!