What do Plant Hardiness Zones mean?


Many beginner and average gardeners have never heard of the term “zone hardiness,” or if they have, they have no idea what it means. The US Department of Agriculture (USDA) has divided North America into 13 different hardiness zones based on temperature and climate. Each one is labeled as zone 1, zone 2 etc. through zone 13.  Zone 1 is the coldest climate and zone 13 is the hottest. Each zone has a 10 degree differential, based on the average minimum temperature of the location, between the previous zone, or, in other words, zone 1s average minimum temperature is 10 degrees colder than zone 2s. They then determine which plants grow best in which zone and recommend a hardiness zone for every plant.

Does the above explanation still have you scratching your head? If so, let’s describe it in a way we can all make sense of. When we go to buy shoes, we all know that we have a shoe size, or a size of shoe that best fits our foot. It is not too small, nor is it too big; it’s comfortable. The same is true with plants. They have a hardiness zone that fits them best. It is where that plant is comfortable and can grow the best. But just like we can sometimes wear a range of sizes, like I can wear a 7.5, 8 & 8.5, plants can sometimes fit into more than one hardiness zone as well. And while our foot size is determined by the foot’s length, a plant’s hardiness zone is determined by the temperature.

Planting a plant in its ideal hardiness zone is important. Just like you would never want to walk around in a shoe three sizes too small for you, a plant does not want to grow in a hardiness zone that is way outside of its comfort zone either. It can be too hot or too cold for the plant, which can result in it failing to thrive, grow or can even cause the plant to die. 

But what happens if you really like a plant and you’re only one zone outside of the recommended hardiness zone? Is it ever OK to make an exception? The answer is yes, it is OK to make an exception. Just like when you fall in love with a pair of shoes and they only have a size 7, when you wear an 8, you make an exception because you love the way they look, but you also know that there are consequences. You may be uncomfortable and it is not the best fit, but you have decided it’s worth it to you. It is exactly the same with plants. It may not be the best fit for them to be one zone outside of their recommended hardiness zone and they may not grow as well as they should, but sometimes you make exceptions and take special care of a plant you really want to have.

Since the hardiness zone is so important, you may be wondering how to tell which zone is good for which plant. Just like shoes are labeled by size, plants are too. The tag on plants contains zone information, saying which zone it grows best in, or you can do an Internet search to find the information. If you ever have any questions on which plants grow best in your hardiness zone or need to know whether a specific plant will grow in a specific zone, a local garden center will be able to help you. 

Happy Gardening!

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