Hardiness Zones and Growing Days

Different areas have different temperatures which would make it hard to know when to plant and harvest. Thankfully we have the USDA Plant Hardiness Zone Map. The map is based on the annual average minimum temperature divided into 10-degree Fahrenheit zones. To be even more precise it's divided even more into 5 degree Fahrenheit zones. My hardiness zone is 5a which means the average minimum temperature is -20 to -15.

Hardiness zones are important when deciding which varieties of plants like grape vines or rose bushes should be planted. In my zone 5a if I planted the wrong type of grape vine it could easily freeze and die. If I planted any kind of citrus tree it would surely die.

Plant Hardiness Zone Map

 More useful information is to know the last day of spring frost, the first day of fall frost and the number of growing days available in your area. From looking at these maps I can see that the last average spring frost is between May 16 - May 31. The average first frost in the fall is October 1 - October 15. That would allow for between 121 and 151 growing days. I know that in my area there has been a last frost in late May and a first frost Sept 22 so my growing days are around 120. Now that I know my growing days I'll be careful not to try to grow plants that take longer than 120 days to mature such as some squash. I also will plant second crops of spinach, lettuce, etc early enough so that they have time to mature.

Day of the Last Spring Freeze Map




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