USDA Plant Hardiness Zones: A Changing Landscape

Your list of planting options got a bit larger due to milder average winter temperatures and urban expansion.

Even the hardiest perennials can die if they are planted in a region that gets too cold so it is wise to know the hardiness zone before you buy a plant that could die in a cold snap.

If you look at a tag before buying a plant, chances are it lists the minimum temperatures it can tolerate based on the USDA plant hardiness zone map.

It is a valuable tool for gardeners and landscapers that lists our area in northeast Florida between 9a or 9b.  Plants rated for 9b could be damaged below a range between 25 to 30 °F and 20-25 °F for 9a.

The map is divided into 13 zones, with Zone 1 being the coldest and Zone 13 being the warmest.

Just before the start of this years winter season, half of Duval County was adjusted warmer since its last update in 2012. Jacksonville previously split between zones 8b and 9a is now primarily in zone 9a, with the western portion remaining in 9a and the eastern part, including the areas inside and east of I-295, in the slightly warmer 9b zone.

The USDA plant hardiness zone map has been around since 1960 and has been updated several times since then. About half of the country is now placed a half zone warmer than they were in the last 2012 update.

USDA’s Agricultural Research Service determines the average annual extreme minimum temperature at a given location using a 30 year time period.

The results are not meant to be interpreted as the coldest it can get in a location but simply the average lowest winter temperature for the location over a specified time.

Remember, occasional cold snaps can still damage susceptible plants, but the shift means plants traditionally suited for warmer zones, like some tropical and subtropical species, have a better chance of thriving in Jacksonville.

Map developers caution against attributing climate change as the sole revision component. The latest map uses more data from 13,412 weather stations compared to 7,983 in the previous map, and newer statistical methods result in a more detailed and accurate picture of temperature patterns.

Comments are closed, but trackbacks and pingbacks are open.