Conservatory Garden, Central Park, NYC, Jan. 30
I used to garden in NE Pennsylvania where I had my Flower and Herb farm. It was in Horticultural Zone 5B at the time, showing that the average daily low temperature was-15 to -5 F. The new USDA horticultural Zone map published last week shows that that area of the coal region is now in Zone 6B.
When I moved to NYC, I was in Zone 6B. Now I garden in zone 7B according to the new USDA map. The data on which the map is based comes from 8,000 weather stations across the U.S. and shows that average low temps have shifted about 5 degrees upward since 1990. In practical terms it means that plants you once coveted for your garden may now be hardy; plants once on the hardiness borderline for your garden will probably now survive. Click here to see the new zone map.
The last map was released by the USDA in 1990; the new one is online and interactive. Once you go to the site and enter the captcha letters which are case sensitive, enter your zip code for a zone reading that takes into account altitude, winds, and other factors.
MicroclimatesWhat the map can never take into account are your microclimates, warmer or colder spots in your own garden. I garden in NYC on a windy roof top so what is that zone? I compensate for the wind by placing a precious crimson bark maple near a south-facing brick wall where it will be protected.
When I visited the Conservatory Garden in Central Park yesterday, I walked down the flight of 18 steps from street level at 5th Ave. to a nice sunken, protected bowl. Clumps of crocus leaves are nicely formed, the daffodil foliage has sprouted and the quince bushes have started to bloom. On my street, only 28 city blocks but a world away, these bulbs are still hidden underground and the quince buds are hardly swollen.
On a garden tour of San Antonio TX ten years ago I was startled to learn that the famous River Walk meandering through the downtown was a whole Zone warmer than the sidewalk at street level, a one 'story' above.
So read the new map, pay attention, then evaluate your own space and take whatever risks you want.
It's a Wrap
If your climate is really too cold for your tree you can always wrap it to keep warm like this one on York Ave.