Average Date of Last Killing Frost

Most planting and seed sowing instructions are based on the average last frost date, which is defined as "the last day in the spring that you might have a killing frost".
When making your plant selections, it is wise to consult more experienced gardening friends and neighbors for advice regarding possible local micro-climates or unusual conditions. Their knowledge can be invaluable.

       

Temperature Conversion Table

Temperature ranges of Plant Hardiness and Gardening Zones

Zone	Fahrenheit	Celsius	Example Cities
1	Below -50 F	Below -45.6C	Fairbanks, Alaska;   Resolute, Northwest Territories (Canada)
2a	-50 to -45 F	-42.8 to -45.5 C	Prudhoe Bay, Alaska;   Flin Flon, Manitoba (Canada)
2b	-45 to -40 F	-40.0 to -42.7 C	Unalakleet, Alaska;   Pinecreek, Minnesota
3a	-40 to -35 F	-37.3 to -39.9 C	International Falls, Minnesota;   St. Michael, Alaska
3b	-35 to -30 F	-34.5 to -37.2 C	Tomahawk, Wisconsin;   Sidney, Montana
4a	-30 to -25 F	-31.7 to -34.4 C	Minneapolis/St.Paul, Minnesota;   Lewistown, Montana
4b	-25 to -20 F	-28.9 to -31.6 C	Northwood, Iowa; Nebraska
5a	-20 to -15 F	-26.2 to -28.8 C	Des Moines, Iowa;   Illinois
5b	-15 to -10 F	-23.4 to -26.1 C	Columbia, Missouri;   Mansfield, Pennsylvania
6a	-10 to -5 F	-20.6 to -23.3 C	St. Louis, Missouri; Lebanon, Pennsylvania
6b	-5 to 0 F	-17.8 to -20.5 C	McMinnville, Tennessee;   Branson, Missouri
7a	0 to 5 F	-15.0 to -17.7 C	Oklahoma City, Oklahoma;   South Boston, Virginia
7b	5 to 10 F	-12.3 to -14.9 C	Little Rock, Arkansas;   Griffin, Georgia
8a	10 to 15 F	-9.5 to -12.2 C	Tifton, Georgia;   Dallas, Texas
8b	15 to 20 F	-6.7 to -9.4 C	Austin, Texas;   Gainesville, Florida
9a	20 to 25 F	-3.9 to -6.6 C	Houston, Texas;   St. Augustine, Florida
9b	25 to 30 F	-1.2 to -3.8 C	Brownsville, Texas; Fort Pierce, Florida
10a	30 to 35 F	1.6 to -1.1 C	Naples, Florida; Victorville, California
10b	35 to 40 F	4.4 to 1.7 C	Miami, Florida;   Coral Gables, Florida
11	above 40 F	above 4.5 C	Honolulu, Hawaii;   Mazatlan, Mexico