Bad to the Zone: Knowing Your Hardiness Zone

Joel Hitchens

Since I moved to San Diego from New England, I have been astonished at how different the environment is. Between the plants, the biodiversity, and the sunshine it is quite an adjustment! What I hadn’t thought about at first, but what has been sinking in more as I attend more farmers markets is just how different the harvesting seasons are. This got me thinking about the tremendous difference in climate and how different the experience is for plants. Where I’m from there is effectively no harvesting of any outdoor plants between November and April. Plants have to experience potentially sub-zero temperatures, several feet of snow, and bitter winds. It’s a testament to the strength of plants that so many manage to make it through!

Although Southern California and New England represent a fairly extreme difference in climate, they illustrate the significant impact that climate has on the variety of plants that you can grow successfully. Hardiness Zones are geographic bands that are defined by the average annual minimum temperature of an area.  Now there is a degree of variability in extreme minimum temperatures, especially due to climate change and the temperature variability that it causes. While temperature is only one factor of growing plants successfully, it is an incredibly important element to consider when deciding what plants you are going to use to fill your garden. When I used to work at a flower nursery I would regularly see people buying plants that were best suited to the 6b-7b zone. Admittedly I still don’t understand why we were even selling plants suited for those zones, but that’s besides the point. People would be disappointed when the flower wilted or, if it was a perennial, didn’t return the next year. While it might not seem like a big difference going between 6a or 6b, planting in the right zone can make all the difference for your plants. Even if the lowest temperature the prior year had been -4º it only takes one day of -9º to kill the plant. It is best to select plants that are well within the range of where you live so that they will not be susceptible to temperature variabilities.

When you are buying seeds and sprouts to grow in your garden, they will usually have a label that indicates their ideal Hardiness Zone. This is often expressed as a range, such as in this example of a Perennial Salvia tag on the right. However if you are trading seeds or doing a plant exchange you probably won’t have a label, so I recommend looking online to make sure you are getting something that is suited for your zone. You don’t want to realize too late that you got something better suited to a much hotter or colder climate than where you live! 

To get a more specific answer on which zone you reside in, the USDA has a zip-code search and an interactive map you can use!