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This is a gardening blog by a guy who dared to veer off the beaten path and discovered plants and gardening along the way. Join me as I write about my processes and inspirations from my “Midwest” point of view.

If you are new to gardening, it’s important to know what Hardiness Zone you live in. To find out more, click here.

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« Floricordially Yours – Part 2 | Main | Houseplants Crying Out in Winter »
Saturday
Feb262011

Hardiness Zones explained

I know, I know. The map looks crazy and confusing will all the colors, but it’s quite easy to figure out. I’ll tell you how.

If you’ve ever shopped for plants, you’ve no doubt noticed some information about Hardiness Zones either on the tag or in the description. A Hardiness Zone for plants helps you know what will grow in a given area. Simply put, not all plants will grow where you live. It’s either going to be too hot or too cold for some plants to survive. Knowing your own Zone will make you a smarter consumer saving you time, money, and frustration by purchasing those plants which have the ability to survive winter conditions in your area.

The USDA Hardiness Zone Map is considered the standard measure for plant hardiness throughout the United States. To find your Zone, click on the link below. The map is interactive- simply enter your zip code to find your zone.

http://planthardiness.ars.usda.gov/PHZMWeb/

Pretty simple. The map tells you exactly what your Zone number is. It even breaks down further by A or B (i.e., 5A or 5B), but generally the whole number is all you really need to know.

How the map came to be

Several years ago, botanists and horticulturists began gathering weather records in North America and recording average coldest temperatures for each region. The records were condensed and grouped into temperature ranges. Each range became a “zone” and mapped onto a map of North America, hence the formation of the USDA Plant Hardiness Zone Map.

About the Zones

There are 13 Zones in North America. Zone 1 is the coldest and Zone 13 is the warmest. Z13 is found only in Hawaii and Puerto Rico. The coldest zones are generally found at higher latitude and higher elevations. 

Tip: The higher the number, the warmer the zone

How to read plant tags and descriptions

Whether you shop online, by catalog, or at a nursery or garden center, most hardy plants will give you some sort of hardiness zone information. 

  • If it is phrased “to Zone 5,” that generally means that the plant will survive the winters in Zones 5 and warmer.
  • If it gives you a range (i.e., Zone 3 to 9), that means the plant will only grow in those zones and not likely to survive outsize of that range.

Remember, the hardiness zone map is a very good guide, but it’s up to you to determine for yourself what will and won’t work in your garden.

Reliability of the map

As I mentioned before, it’s not completely reliable because factors other than cold temperatures impact plant survival. One must also consider things like soil type, rainfall, daytime temps, hours of sunlight, wind, humidity, and heat. Regions with the same zone number can differ from each other in many ways.

For instance, I live in Indianapolis, IN in Zone 6. There are portions of Arizona that are also Zone 6, but I’m certain our climates have little in common other than how cold our winters can get. You can also have microclimates with your immediate area which can affect how plants grow. The good news is your local nurseries and garden centers are inclined to mostly carry what works in your zone and very few things that are outside of your zone. Read the plant tags to be certain.

What’s a microclimate?

A microclimate is essentially a climate that differs from the surrounding area due to variations in the environment. Examples include walls and structures, hills/slopes, bodies of water, etc. All of these can create a microclimate which can range in size from a few square feet, to a square mile. A house or garage can reflect sun onto the ground and block wind all year round creating a microclimate in that particular area of your yard.

Final Thoughts

It gets tricky where one zone borders another. Remember the map is only a guide, albeit a very good guide. You may find that some plants designated for your zone won’t make it while others not designated for your zone will. Be wise and stick mostly to plants designated to your zone– those best suited for growing and surviving in your neck of the woods.

 

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