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Pittsburgh, Pennsylvania Hardiness Zones

Posted by on Jan 30, 2010 in Climate, General Thoughts | 3 Comments

*Click here for an Update*

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A short discussion on the hardiness zones in and around Pittsburgh, Pennsylvania and how they are changing.

The old USDA hardiness zone map issued in 1990, which incorporated data from 1974-1986, places Pittsburgh well within zone 6 with zone 5 not far off to the north. If you follow our longitude, you would not run into zone 7 until somewhere around the Virginia, North Carolina border.

old hardiness zone map

The 1990 USDA hardiness zone map.

We all know things have changed since 1990 and the map was supposed to also, but the new map, due in 2005 was never released. There is a lot of speculation about why it wasn’t released due to the administration at the time and their stance on climate change. Whatever the reason (I have read it was because it wasn’t interactive enough as a digital-based map or that the USDA wasn’t satisfied with a 15 year data set) it is now 5 years since a new version of the USDA hardiness zone map was due and we still don’t have an update.

Fortunately, the National Arbor Day Foundation took it upon themselves to update the map. Using the same sources of data that the USDA used to create its 1990 map, and a fifteen year set of data (three years longer than the previously accepted 1990 map) the National Arbor Day Foundation released a map in 2006.

updated hardiness zone map

The 2006 Arbor Day Foundation Hardiness Zone Map created using 15 years of data from the same sources the USDA used for its earlier map.

the changing hardiness zones of Pittsburgh, Pennsylvania

A zip-code search for my house indicated that Pittsburgh is in zones 6-7 according to the Arbor Day Foundation map.

As you can see there are some very significant changes for the Pittsburgh area and Pennsylvania in general. Zone 5 has retreated far to the north, only expressing itself in the north central part of state, Zone 6 is firmly settled in our region, perhaps even slightly north, and most surprisingly, you can see a spot of zone 7 sitting right in the Pittsburgh locale (the search of my zip-code confirmed this, see the image to the left).

The following maps compare the 1990 USDA version (with subzones concentrated into their larger categories) with the updated 2006 version published by the Arbor Day Foundation. The lighter red swaths striping the country indicate those areas have increased one full zone from the map published twenty years ago.

global warming effects hardiness zones

So does this mean I’ll soon be growing date palms and citrus. Most likely, no. As this past year has proved, though the planet continues to heat and climate shifts, our weather will not follow the same patterns it once did only a few degrees warmer. In fact these global changes have and will continue to cause increased variability in the weather.

Keep your eyes peeled for the release of the updated USDA map, which was supposed to be out in 2009, but again they missed the deadline. I will let you know if I hear anything.


*Much of the information in this article comes from the USDA, The National Arbor Day Foundation, and Raintree Nursery.

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*February 2011 Update*

I emailed the USDA to get clarification on the new map, here is their response:

We do not provide forecasts of when a publication, which the USDA Plant Hardiness Map counts as, even throughthe new one will be first available on the web.  Two prototypes have been created to allow for the analysis of issues that still need work, but the map itself requires that a contractor “build” the application that will actually be hosted on line as the map.  If you speak computer geek, you will understand how “application” differs from a simple prototype.

The process of setting up contracts for the application to be built and for the web hosting so initial demand do not crash ARS or USDA servers (as happened when My Pyramid first went on line to much larger initial demand than expects), have been slowed and complicated by several factors, among them the general government procurement, the lack of a budget being passed which can preclude spending money), and the increasingly complicated security processes for government web sites that have to be met and dealt with.

Prior to the advent of some new technology (we are not getting out of my depth with computer systems knowledge, so I am parroting our IT people now), the size of the database for the interactive map and the large expected numbers of viewers, especially in the beginning, made it very difficult to find the vendors we need.  Cloud computing and other advances have offered some new avenues, but government procurement requirements make inching toward contracts a long process.

Once we have application design and hosting contracts in place, it will take about four months to have the website available.


  1. Larry
    February 6, 2010

    Maybe not palm and citrus, but how about fig?

  2. Michele
    February 12, 2010

    I have 3 figs planted on the South/West side right up against my house…they get full sun most of the day during the summer! I am hoping (because I covered them for the winter) that they will come back this spring! The house should supply them with additional heat….I got them from a Pennsylvania grower who told me if I do it this way…they will come back! I will post my results in the spring!

  3. Peter
    May 11, 2010

    Just wanted to let you know that there is an interactive google maps based USDA hardiness zone map focusing on Pennsylvania

    I thought this might be a great resource for Pennsylvania gardeners accessing your site.



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