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kevinrs · March 10, 2012

I'd say unless there is a problem, keep doing what you are doing. A higher zone number just means it doesn't get quite as cold in the winter.
The map is only based on average annual extreme minimum temperature. Meaning from 1976-2005 what was the absolute coldest it got on the coldest night each year, those 30 temperatures are added up and divided by 30 to get the average, this was done for each weather station they have, assigning colors to temperature ranges, and the map was computed to fill in the space between the stations based on terrain, slope, closed valleys, trees, etc.

It's real purpose is finding what perennial plants and trees should survive the winter in an area. Basing a planting date off the map isn't very good, because some places have the same color on the map, but warm up in the spring at different rates.

March 10, 2012	#27
kevinrs Tomatovillian™ Join Date: Feb 2011 Location: Littlerock, CA Posts: 218	I'd say unless there is a problem, keep doing what you are doing. A higher zone number just means it doesn't get quite as cold in the winter. The map is only based on average annual extreme minimum temperature. Meaning from 1976-2005 what was the absolute coldest it got on the coldest night each year, those 30 temperatures are added up and divided by 30 to get the average, this was done for each weather station they have, assigning colors to temperature ranges, and the map was computed to fill in the space between the stations based on terrain, slope, closed valleys, trees, etc. It's real purpose is finding what perennial plants and trees should survive the winter in an area. Basing a planting date off the map isn't very good, because some places have the same color on the map, but warm up in the spring at different rates.