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Have you ever heard someone mention their growing zone or hardiness zone? You may have wondered, what are the hardiness zones? Well friends, I am here to not only explain what the hardiness zones are, but also what zone you are in, and how that impacts your gardening.
The USDA hardiness zones are a set of zones developed by the United States Department of Agriculture (USDA) to help farmers and gardeners better understand the climate that they are growing in. The hardiness zones divide the United States into regions (or zones) based on the average annual minimum temperature. Each zone has a temperature range of 10 ℉. The zones range from Zone 1, with an average low of -60℉ to -50℉ (-51.1℃ to -45.6℃), to Zone 13, with an average low temperature of 60℉ to 70℉ (15.6℃ to 21.1℃ ).
The current map that is used as the standard for determining which zone you live in was released by the USDA in 2012. The USDA took data from a 30 year span (1976-2005) in order to provide the most accurate information possible. If you are interested in checking out the USDA hardiness zone maps from 1960 and 1990, the USDA website still has them!
While this is an incredible resource, I do want to stress that it only tells you the average minimum temperature in your area. The zones do not take into consideration other weather conditions such as humidity and rainfall. Just because someone else has the same growing zone as you, does not mean they will have the same growing conditions year-round.
Subzones
The hardiness zones can be even further broken down into subzones. These subzones only cover a 5℉ range of minimum temperatures. For example Zone 10 is broken into Zone 10a and 10b. Zone 10a experiences freezing temperatures with average lows reaching 30℉ to 35℉ (-1.1℃ to 1.7℃). Meanwhile Zone 10b only has average lows of 35℉ to 40℉, meaning that growers in that zone never experience a freeze. This illustrates why subzones are so important. While a tropical plant may thrive in Zone 10b, it could really struggle in Zone 10a if they experience a frost.
Which Plant Hardiness Zone am I in?
Okay, now that you understand what the hardiness zones are, it is time to figure out yours. If you want to go straight to the source, check out this interactive map on the USDA website! You can either explore the interactive map, or simply type in your zip code at the top of the page to find your USDA plant hardiness zone. You can also simply type “USDA hardiness zone (your zip code)” into Google and the information will come right up!
Why do Hardiness Zones Matter?
Great! Now we have learned what the hardiness zones are, and what zone you live in. The next step is understanding why it matters to you and your garden.
The USDA hardiness zones matter in your garden because they provide a guideline for what will and will not be perennial in your area. For example, most places across the United States freeze in the winter. If it freezes in your zone, you will probably not be able to grow tropical plants.
Purchasing Perennials
If you are looking at investing in perennial plants, such as fruit trees, it is very important to know your hardiness zone. Different fruit trees can withstand different temperatures, and I don’t just mean different types of fruit. There are different varieties of each type of fruit tree and those varieties have different weather preferences. For instance, some varieties of peach trees can handle colder temperatures (down to Zone 4), while others are better suited to handle the heat and grow well in Zone 9. Knowing your hardiness zone will give you a starting point when selecting the correct trees for your property.
As I mentioned earlier, your hardiness zone will only tell you the average minimum temperature. It does not take anything else about your climate into account. There are other factors to take into consideration when purchasing perennial plants such as chill hours, rainfall, the number of frost free days you have, and high temperatures.
If Something is Not Hardy in my Zone, Does that Mean I Can’t Grow it?
So you’re at the plant nursery and the tag on the plant says it is not hardy in your zone. Does that mean you can’t grow that plant on your property? The answer is, it depends! How many zones difference is it between the zones that the plant will thrive in and your zone? If it is more than one or two zones colder than your climate, it will prove very challenging to grow that plant outdoors. What lengths are you willing to go through to protect that plant from the cold temperatures?
Let’s Talk Citrus!
For demonstration purposes, we are going to discuss citrus. Most citrus plants are only hardy in zone 8 through zone 10. However, if you live in Zone 7 you still may be able to grow citrus. First, check to see if there are any varieties of citrus that ARE hardy in your zone. If not, consider the following:
- Do you have a greenhouse or high tunnel you could grow the citrus in that stays warm enough?
- Are you willing to put supplemental heat in that structure to maintain the correct temperatures?
- If you get dwarf citrus trees are you willing and able to give them a sunny spot in your house all winter?
- Do you have a spot with a microclimate that is warmer than the rest of your property? Depending on how sunny it is where you live in the winter, a brick wall, or other structure, can hold a lot of heat and protect your plants.
If you answered yes to any of these, you may be able to grow citrus. There is still a risk, but I would say that it is worth a shot! If you said no to all of these, you are unlikely to have much success growing citrus.
Other Perennials
Another thing to consider is that some perennials can be grown just fine as annuals. For example, many perennial herbs such as thyme, oregano, and rosemary can be grown as annuals without a problem. While most areas can grow these herbs as perennials, it is important to recognize that they don’t need to grow for multiple seasons before they start producing.
Artichokes are a similar story. Although they are a perennial in very warm climates, others may be able to grow them just as an annual. As long as your growing season is long enough, first year plants will produce artichoke heads and flowers for you to enjoy!
Perennials are a vital component of many gardens and homesteads. You now hold the knowedlege to be able to choose the correct perennials for your area. If you want to learn more about perennial and annual plants, I have a blog post on that too! Now that you are fully equiped with all the knowledge you need about the USDA plant hardiness zones, I hope you feel empowered to get growing!
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