http://www.usna.usda.gov/Hardzone/hrdzon3.html
Introduction
This map supersedes U.S. Department of Agriculture Miscellaneous Publication 814, "Plant Hardiness Zone Map," which was revised in 1965. This 1990 version shows in detail the lowest temperatures that can be expected each year in the United States, Canada, and Mexico. These temperatures are referred to as "average annual minimum temperatures" and are based on the lowest temperatures recorded for each of the years 1974 to 1986 in the United States and Canada and 1971 to 1984 in Mexico. The map shows 10 different zones, each of which represents an area of winter hardiness for the plants of agriculture and our natural landscape. It also introduces zone 11 to represent areas that have average annual minimum temperatures above 40 F (4.4 C) and that are therefore essentially frost free.
Probably the most important consideration in determining what garden and landscape plants
you can grow in your garden is whether or not they will survive the climate in your area.
The USDA Plant Hardiness Zone Map factors in average winter minimum temperatures. This collection of information starts with Zone 1, where minimum temperatures can go down to MINUS 50 degrees Fahrenheit, and ranges to Zone 11, for the lucky gardeners in Hawaii and extreme Southern Florida where lows don't drop below 40 degrees Fahrenheit.
The data on which the USDA map is based was gathered over a period of 60 years.
Hello, I am checking the temperature zone for my city West Palm Beach. This website says im zone 10a with an average annual minimum of 30. I can tell you right now this is not true, maybe it was in the past. I have never experienced any frost in West Palm Beach and I was born there and lived all my life in that city. Guys, check the temperatures from 1990 to 2006(winter of 2007 isnt over yet) and average them up to get an update for your zone and any other city zones you want. Be sure to check at least 5 months(from November to March) If there is a tie with more than one day with the same minimum, choose one. The USDA Plant Hardiness Zone Map was last revised in 1990 so its 17 years outdated.
West Palm Beach, FL annual minimum for 1990-2005:
1990 January 13, minimum 46.
1991 February 16, minimum 37.
1992 January 16, minimum 42.
1993 March 15, minimum 41.
1994 unknown
1995 unknown
1996 unknown
1997 January 19, minimum 36.
1998 February 8, minimum 45.
1999 January 6, minimum 41.
2000 January 27, minimum 36.
2001 January 1, minimum 36.
2002 January 4, minimum 36.
2003 January 24, minimum 34.
2004 December 15, minimum 41.
2005 January 24, minimum 38.
2006 February 14, minimum 36.
I used wunderground com for this data. For some reason they have no data for three years(not bad out of 17 years). Just dont include them in the average. Ok add up all the years with data then divide.
46+37+42+41+36+45+41+36+36+36+34+41+38+36=545/14=38.9
This pretty much makes us zone 11 if we round to the nearest zone(see image) Also I have never seen frost/snow in my life so id consider West Palm Beach to be tropical!
Franklin/Oil city, PA annual minimum for 1990-2005:
1990 February 26, minimum -4.
1991 January 22, minimum 2.
1992 January 19, minimum 2.
1993 December 27, minimum -4.
1994 unknown
1995 unknown
1996 unknown
1997 January 19, minimum -7.
1998 December 23, minimum 5.
1999 March 8, minimum -2.
2000 January 22, minimum 0.
2001 January 3, minimum 6.
2002 December 4, minimum 3.
2003 January 27, minimum -4.
2004 January 25, minimum -7.
2005 January 28, minimum -5.
2006 February 19, minimum 1.
(-4)+2+2(-4)(-7)+5(-2)+0+6+3(-4)(-7)(-5)+1=-15/14=-1.1
This makes Oil city/Franklin zone 7a, but for those who are conservative, they would probably consider it zone 6b because theres a 50% chance annually of seeing at least one day in the low minus.
Parkersburg(near Woodsfield, OH), WV annual minimum for 1990-2005:
1990 December 23, minimum 3.
1991 February 16, minimum 6.
1992 January 19, minimum 1.
1993 February 19, minimum 2.
1994 unknown
1995 unknown
1996 unknown
1997 January 19, minimum 0.
1998 December 25, minimum 8.
1999 January 5, minimum 0.
2000 January 22, minimum -5.
2001 January 3, minimum 7.
2002 January 1, minimum 5.
2003 January 27, minimum -5.
2004 January 31, minimum 0.
2005 January 24, minimum 1.
2006 February 19, minimum 2.
3+6+1+2+0+8+0(-5)+7+5(-5)+0+1+2=25/14=1.8
Zone 7a, but the average temperature appears 5-7 higher than
Oil city/Franklin. The summers definately get hotter and stay hot
much longer as well. Can get cold but those cold snaps are generally
brief and most winter days have highs above freezing.
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