Match Maker: Picking the Right Shrub/Tree for Your Area

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Southwest Yard & Garden by Dr. Marisa Thompson

The ‘Sea Green’ juniper, shown here in Santa Fe, is a wide-spreading shrub known for tolerating poor site conditions and growing wider than anticipated. Photo credits Tracy Neal.
2012 USDA Plant Hardiness Zone Map of New Mexico (USDA-ARS and Oregon State University; https://planthardiness.ars.usda.gov/PHZMWeb/Downloads.aspx)

Question: After I bought a ‘Sea Green’ juniper I noticed the tag said “Hardy to 20°F.” Well, I live at almost 7,000 feet in Torrance County. When I looked online it said my zone is 6. I think maybe the tag is wrong. Do you agree?
-        Carolyn M., Torrance County

Answer: I’m not familiar with the ‘Sea Green’ juniper, so I did a quick search and confirmed that the recommended planting zones for that tree are USDA Hardiness Zones 4–9. I also double checked the USDA Hardiness Zones for your county, which tend to be in Zones 6–7. You can find the USDA Hardiness Zone for your location at https://planthardiness.ars.usda.gov/. As described on that website, the 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. For example, USDA Hardiness Zone 6 has average annual extreme minimum temperatures from -10°F to 0°F, and Zone 7 is slightly warmer with average annual extreme minimums from 0°F to 10°F. Since the plant you bought is recorded as being cold hardy to a safe minimum of Zone 4, with average extreme cold temps down to -30F, there’s a really good chance it will survive winters in your general area.

2012 USDA Plant Hardiness Zone Map (USDA-ARS and Oregon State University; https://planthardiness.ars.usda.gov/PHZMWeb/Downloads.aspx).

The average extreme low temperatures vary based on which years the data averages came from. For the 2012 USDA Plant Hardiness Zone Map, the zone assignments are based on data from 1976–2005. Because average temperatures are going up with climate change, we can expect the assigned zones for different regions to change too, but not as uniformly as you might think. It’s not that simple. Even as average temperatures rise, we’re still expected to get cold snaps and polar vortexes. So while the extreme minimum temperature data used to assign USDA Hardiness Zones are changing slightly with global warming, it’s those high temperatures that keep breaking records and will continue to do so.

Lately, I’ve gotten many questions about ailing trees and shrubs around the state, and I tend to get more worried about plants not being heat hardy enough for where they’re planted. Usually when a range of zones is given for a plant (e.g., USDA Zones 4–9), that higher number implies the hottest cold hardiness zone it can tolerate. So it seems you’re in the clear on that spectrum too with your new juniper tree. In the next 30 years, high temperatures in the Albuquerque area are expected to resemble the current high temperatures in Las Cruces or El Paso, and in 80 years, by 2100, closer to the highs currently experienced in Tucson. For perennial plants to live and thrive as long as possible, we need to consider how cold hardy they are today and how heat hardy they will be in warmer decades to come.

It’s always important to double check these planting details. In this case, the label seems to have been misprinted, but you’re still in the clear. Thank you for planting shrubs and for paying attention to these important details.


For more gardening information, including decades of archived Southwest Yard & Garden columns, visit the NMSU Extension Horticulture page (http://desertblooms.nmsu.edu/), follow us on social media (@NMDesertBlooms), or contact your County Extension office (https://aces.nmsu.edu/county).
Marisa Thompson, PhD, is the Extension Horticulture Specialist for New Mexico State University and is based at the Agricultural Science Center at Los Lunas.


Edible New Mexico Magazine article crosslink -- GROWING YOUR FUTURE FAVORITE TREE 

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