The USDA Plant Hardiness Zone is commonly known as a gardening zone amongst gardeners. Whichever name you’d like to call it, just make sure you know which zone is yours.
What is a gardening zone?
The Agricultural Research Service (ARS), part of the United States Department of Agriculture (USDA), created a plant hardiness zone map with Oregon State University’s PRISM Climate Group in 2012. The map divides north america into 11 main gardening zones based on average minimum winter temperature. Zone 1 has the coldest average minimal temperature (-50°F) and covers parts of Alaska and Canada. The zones move south from there increasing by 10°F for each zone. Zone 11 has the highest minimal average temperature at 40°F. The majority of Hawaii is in zone 11. The map does extend to zone 12 and 13 though, which are for Puerto Rico and very few parts of Hawaii.
You might notice that these zones are further divided into a and b categories. This is when there is a 5°F difference in average temperature within one zone. I for example am in zone 7a here in northern Virginia, but I started my gardening journey in zone 7b in Alabama. The ‘a’ part means that it is slightly colder here than it is in Alabama. Knowing that both areas are in zone 7 was very helpful when I moved to Virginia and it can be important for you as well.
These gardening zones let gardeners know what the average minimal temperature is in their area so that they can determine which plants will thrive in their garden. Seeds and plants that are for sale usually list the gardening zones that they will perform the best in. By knowing which zone you’re in, you’ll be able to identify the best crops for your area as well as when to plant and harvest them. For me, knowing that I am in the same gardening zone as I grew up in meant that I already knew which plants would thrive in this area.
Why do I need to know what gardening zone I’m in?
Sure you can just pick plants and seeds online or in store and give it a go, but wouldn’t it be better to be a knowledgeable gardener? Throwing caution to the wind can be a lot of fun, and often I find myself saying, “why not” when it comes to gardening. You can try anything once my dad would say. There are some things that just won’t work though and that’s why knowing what gardening zone you are in is important.
I know that in zone 7, I can grow a number of fruits and vegetables, but that the growing conditions aren’t ideal for many of the tropical plants. At the same time, gardeners in very warm zones such as Puerto Rico, won’t be able to grow cool weather crops as well. I won’t be planting any avocado or banana trees here and they won’t likely be planting many barasicas since those are cool weather crops that have a long growing period and Puerto Rico doesn’t have a long cool season.
Why you should know your frost dates?
When looking up your gardening zone, you might notice a reference to frost dates. This is equally as important to know as your gardening zone. You can look up your first average frost date and last average frost date. You’ll want to know what those are so that you can calculate when to plant each crop. Your last average frost date tells you when you should plant to avoid a late Spring frost that could kill young plants and your first average frost date tells you when you need to harvest your least cold tolerant plants in the fall.
In gardening, everything is about timing. While many gardeners are eager to jump start their gardening season as soon as the weather warms up, seasoned gardeners know to wait until the last frost date. The last frost date can be much later than you would think. Here in Virginia in zone 7a our last frost date is April 24th. Many gardeners lost their first round of planting this year however, because there was an unexpected and unusual late frost. The average frost dates are not perfect, but they are exactly as stated, average dates. It’s good to know what your frost dates are so that you can plan accordingly, but know that it isn’t set in stone. Instinct and experience will help you make up the difference.
What if I don’t live in North America?
While the USDA created this plant hardiness zone for North America, there are also specific gardening zones for many countries. Canada, Britain, Australia, New Zealand, China, Japan, and Europe as a whole all have their own gardening zones. If you are in a different part of the world, you can calculate your gardening zone so that you can determine which plants will grow best in your area. To do this, you simply take the lowest average temperature in your area and add 10°F (12.2°C) for each zone.
Knowing your gardening zone can make a difference between a less than ideal garden and a very successful one. When you pick out a plant at a garden center, or even seed packets, look at the tag or reverse side of the seed packet. There you’ll find important growing information such as the amount of sunlight and water plants require as well as what zones they grow best in and when to plant and harvest the crops.
Next time you are looking at adding new plants to your garden, make sure to look at this vital information.