Thanks to a savvy and thoughtful reader, I now realize there has been some discrepancy in my column over the years when referring to our growing zone. At times, I have referred to Broomfield’s growing zone as five; While other times I have stated we are in growing zone six. Mea culpa! I have egg on my face. Or, do I?
After carefully reviewing the information on the USDA plant hardiness zone map, I can say, with confidence, that I was correct both times. However, my answers were incomplete. A portion of Broomfield is in zone 5b, but other sections are in 6a. If you would like to find the official hardiness zone for your particular location, you can enter your street address at bit.ly/3JjUrpJ.
Why is it important to understand hardiness zones? Well, we wouldn’t want to attempt to grow an orange tree outdoors year round here in Colorado or plant tomatoes in February. Hardiness zones help us know what to plant and when to plant it. The zones are based on the average annual low temperature over many years. The difference between zones 5b and 6a is a matter of 5 degrees Fahrenheit.
According to Yale Environment 360, hardiness zones are moving northward in the United States at approximately 13 miles per decade. The last official zone changes occurred in 2012. You can view a map of the zone changes from 1990 to 2012 at bit.ly/3rabzIq.
You can also find some interactive story maps at the USDA website showing recent and projected conditions. The change in growing days, hardiness zones and heat zones is eye opening. bit.ly/38zKvMh.
In addition to your officially designated hardiness zone, there is another important factor to consider – your unique microclimate. Each yard will have not just one microclimate, but several. Here are some examples: trees provide shade, fences act as windbreaks, decorative rocks create heat islands, mulch is a moisture barrier and even the soil type will often vary from one side of your yard to another.
These microclimates are the reason your neighbor has success with a particular type of plant, while yours bites the dust. This is also the reason a plant may flourish on one side of your yard, but not the other.
My best advice is to know your zone, then get to know your yard. Be curious and ask yourself a lot of questions. Where is the sun and shade in the middle of summer versus January? Do plants have any wind protection? Do you have declining trees and shrubs sitting in heat islands burning up? Are you using a natural mulch to help retain moisture? Does water pool anywhere in your yard?
Arianna Kelley Rawlsky has an MS in horticulture and is the director of Bringing People and Plants Together, an organization dedicated to bringing horticulture education and therapy to the community. For more information: PeopleAndPlantsTogether@gmail.com or follow us on Facebook.