JACKSONVILLE, Fla. – We are faced with another freeze tonight, with temperatures expected from the upper 20s to the low 30s, depending on your location. How do you decide which plants need to be covered and which plants will be ok?
Check out this map from the United States Department of Agriculture- its a plant hardiness zone map. The zones are determined by that area's average annual minimum temperature- in other words, the coldest temperature you'll see all year in that location. Northeastern Florida and Southeastern Georgia are Zone 9a and 9b. 9a zones seeing the average coldest temperature between 20° and 25°. Zone 9b sees the coldest temperatures between 25° and 30°.
Plants are also rated by zone, you can look up at plant's zone and that will tell you what minimum temperature it is able to withstand. For example, knockout roses are good for Zones 5+, meaning that they can withstand minimum temperatures down to zero degrees. Poinsettias are good for zones 10+ meaning they will be damaged by temperatures below 30° to 40°.
Here are each zone's average annual minimum temperature range across the US:
|1||Below -50ºF||Below -45.5ºC|
|2||-50º to -40ºF||-45.5º to -40.0ºC|
|3||-40º to -30ºF||-39.9º to -37.2ºC|
|4||-30º to -20ºF||-37.1º to -28.9ºC|
|5||-20º to -10ºF||-28.8º to -23.4ºC|
|6||-10º to 0ºF||-23.3º to -17.8ºC|
|7||0º to 10ºF||-17.7º to -12.3ºC|
|8||10º to 20ºF||-12.2º to -6.7ºC|
|9||20º to 30ºF||-6.6º to -1.2ºC|
|10||30º to 40ºF||-1.1º to 4.4ºC|
|11||Above 40ºF||Above 4.5ºC|
Once you know what the minimum temperatures that that particular plant can withstand, you can check with The Weather Authority to see what the temperatures will get down to in your neighborhood to determine whether you should cover the plant or not.