Understanding the USDA Hardiness Zones


I’ve lived everywhere. Well, it feels like it anyway. Grew up in Louisiana, spent some time in Maryland while in the Army, some transitional time in Mississippi, escaped to Alaska for a couple of years, and established roots in Idaho. Believe it or not, but we have left Idaho twice and moved back each time: Once for a 2 year reunion in Louisiana and once for a year and a half trial in Tennessee. I’ve grown gardens in all kinds of environments and climates (and killed a good many along the way). There’s one thing I learned about growing stuff in different climates: Don’t fret over what you can’t grow and focus on what you can grow and your garden will flourish. Understanding the USDA Hardiness Zones will help you focus on those plants to better ensure a successful season.

I am going to go out on a limb here. You live somewhere on the Earth and that “somewhere” has specific climate benefits and restrictions. Me? I live in Southwestern Idaho (Zone 7a : 0 to 5 (F)). We lived in Alaska for a couple of years after growing up in Louisiana. These, two season zones (Anchorage Zone 4b : -25 to -20 (F) and West Monroe Zone 8b : 15 to 20 (F)) have two things in common. They both have only two seasons: Louisiana with its Summer and January and Alaska with its Winter and July. You’ll be able to grow cabbages most of the late fall and winter months in Louisiana where there’s NOTHING growing in Alaska and yet grow cabbages the size of tractor wheels in Alaska during the summer when any attempt at growing anything Brassica genus in Louisiana will either be impossible or cause you to pull your last hair from your balding head!

What zone are you in specifically. Understanding the USDA Hardiness Zones is easier when heard from the horse’s mouth. The USDA has a website that will tell you exactly what zone you are in. From the USDA Plant Hardiness Zone Map web site:

“The 2012 USDA Plant Hardiness Zone Map is the standard by which gardeners and growers can determine which plants are most likely to thrive at a location. The map is based on the average annual minimum winter temperature, divided into 10-degree F zones.”

Understanding the USDA Hardiness Zones understanding the usda hardiness zones Understanding the USDA Hardiness Zones USDA Zone Site

The USDA has an awesome interactive map that you can work with to find your specific zone. Here’s the link (a new window will open): http://planthardiness.ars.usda.gov/

You notice all the little bands of color from southern peach to northern pink. Each color differs in temperature from one color to another by about 10 degrees (F). Each color zone is subdivided into mini zones that differ from about 5 degrees (F). Each mini zone is designated by the letters “a” and “b.” The colors and associated letters indicate lowest or highest temperature in their area during a normal year (as per the record shows for the past 30 years).

There are a couple of factors to keep in mind.

Microclimate. When we lived in Idaho on that nice little ½ acre spot (see the first few videos on my YouTube channel: https://www.youtube.com/c/sulaearts) we had created a microclimate. Our temperature on our side of the fence was usually cooler by 3-4 degrees from our neighbor’s open, bare lots. The packed-in plants and watering we did created a humid pocket of air that enveloped our “back 40.” Your efforts may very well alter your growing climate and create a “mini zone” specific for your spot. Despite the USDA Zone recommendations, if you plant something that is not suggested for your Zone but the plant comes back each year and is flourishes on your homestead; more power to you! You just keep on keepin’ on.

Infrastructure. You may have a plant that, given normal growing conditions, generally does not grow well in your Zone but does awesome year after year on your spot because it is planted in such a way as to allow just a bit of protection from the winter’s cold or the summer’s heat. We have a hard time growing rosemary here in Southwestern Idaho. If I put it out in the open near things like my lavender and sage, it dies over the winter. And that’s too bad because I love the way rosemary smells and tastes. But, when I plant the herb near the house on the south-facing side, it comes back each year. The house generates and holds onto just enough warmth to allow the rosemary to survive the very cold winters we have here in our Zone 7a. It is suggested that “In zone 7 and colder, try growing rosemary in a container you can bring inside in cold weather.” I get excited when spring comes and my rosemary “wakes up.” Ahhhh, the joy of small things life has to offer.

Here’s one more tid-bit of information: If you are growing in pots, you will take your Understanding the USDA Hardiness Zones and add a bit more information to ensure your potted plant will survive the winter. Add two zones to your zone when considering a potted plant. Otherwise, you will want to secure your potted plants indoors or in the garage to protect them during the winter months. Potted plants don’t have the protection of the solid earth and the crown and roots are up and in the cold, unprotected are.


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