Planting Zones Interview

Lance Walheim
Lance Walheim

Do you understand what planting zones are? Do you know how to use them to improve the success of your garden? The following interview with Bayer Advanced Garden Expert, Lance Walheim, will give you new insight on the subject of planting zones and how they affect you and your garden.

Importance of Planting Zones

LoveToKnow (LTK): What are Planting Zones?

Lance Walheim (LW): USDA planting zones are based on average minimum winter low temperatures determined by historical weather data. I think the latest version came out in 1990 and they are working on a new one. There are also heat zones which help determine how far south plants can be grown. Vegetables and annuals are planted by average frost dates, which are also mapped. The following link offers more information:

LTK: Why is it Important to Understand Planting Zones?

LW: It's the easiest way to get a general idea if a plant will survive in your area. However, other things like sun, shade, soil and moisture also play important roles; sometimes even more important.

Zones and Climate

LTK: Has Global Warming had an Effect on these Zones?

LW: There have been some regional changes made in some areas as a result of global warming, but I don't think they are definitive. The National Arbor Day Foundation has shifted some zones farther north, but this has been controversial.

LTK: How Strict are Planting Zones?

LW: They are only a guideline, but they are very useful. Local microclimates will also influence what you can grow. Slope of the land, elevation, large bodies of water, exposure and proximity of buildings, etc. can make areas warmer or cooler than the overall climate region.

LTK: How can Planting Zones be Extended?

LW: By choosing microclimates wisely or by providing winter protection, but its not something I recommend for beginners.

LTK: Is it Possible to Garden in Extreme Zones?

LW: Of course, there are plants that can be grown almost anywhere. Native plants are always the best choice for severe climates.

Other Items of Gardening Zone Interest

LTK: Can You Explain Microclimates?

LW: Microclimates are small climates around your home or neighborhood that differ from the general climate of your area. Take a walk around your home. You'll notice areas that are warmer or cooler than other spots. Check local weather station reports and compare with what you measure around your home. Nurserymen and cooperative extension agents are also good sources of information.

LTK: Can You Explain Heat Zones?

LW: Heat zones are based on the high temperatures at which plants stop growing. There's a whole book about them. Personally, I find them confusing and unreliable. I rarely even look at them.

LTK: What are Sunset Zones?


LW: That depends on which ones you are talking about. The 24 Sunset Western Garden Book zones are for the 13 western states, AL and HA. They are more specific than USDA zones and far superior for western gardeners, taking into account many other factors besides just winter lows. Southern Living also has zones for the south. There was a Sunset National Garden Book that broke the entire country into 40-something zones, but I think it is out of print. (Editors Note: Sunset National Garden Book is available from

Importance of Understanding Your Zone

Whether you are a new gardener, or more experienced, you will see more success in your garden or landscape design if you understand how to utilize your planting zone when making your garden plans. In addition, understanding microclimates and the condition of your individual garden space will aid in your gardening success.

Another great source of information on planting zones is found in most seed catalogs, including what zones are best for each plant.

LoveToKnow Garden would like to thank Bayer Advanced Garden Expert Lance Walheim for taking the time to do this interview. For a free online garden calendar along with podcasts of Lance giving more gardening tips, visit Bayer Advanced.

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Planting Zones Interview