HORTICULTURE COLUMN: What do the USDA Hardiness Zone changes mean for Stanly?

Published 2:54 pm Tuesday, February 20, 2024

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By Andrew Pfeifer, Stanly Horticulture Agent

The USDA Hardiness Zones are utilized by gardeners and other entities to determine what plants will survive when planted in the ground.

There are 13 of these Hardiness Zones in the United States, based on the lowest extreme temperature of the year. Each zone represents an increase of 10 degrees fahrenheit, with the sub zones denoted with “a” and “b” representing a halfway point.

The Zone Map was updated in fall of 2023, revised from the previous version created back in 2012. As a result, many areas have received new data including North Carolina.
Previously, Stanly County was considered to be in USDA Hardiness Zone 7b. Now it is classified as Zone 8a, indicating a warmer winter average over the past decade. However, one may wonder what this ultimately means for county residents.
Fortunately, this change is less important than one may think. USDA hardiness zones are simply a starting point to determine success and potential survivability in the landscape.

In reality there are multiple factors that are taken into consideration to predict cold hardiness:

1. Plant Species – Some species are hardy in much colder zones, indicating that our winter freeze is hardly an issue.

Likewise, there are many plants that cannot handle any cold weather regardless of zone.

2. Location – Sun exposure, proximity to structures and land elevation are all important factors that can impact how cold weather behaves.

Sun exposed walls can remain warmer than surrounding areas and can protect plants more sensitive to frost conditions.

These types of situations are called microclimates.

3. Containers vs Ground – Pots are significantly less insulated than the actual soil, leaving containers more vulnerable to freezing. In ground plants can be further protected with mulching. Fortunately, containers are also much easier to move to a protected location such as a shed or garage. Some plants may also be brought indoors, especially if they do not go dormant (such as a lemon tree).

Overall, our change to Zone 8a has very little impact on what can be grown successfully year round in our county. However, in the past 30 years several plants have become properly cold hardy and can be grown with confidence. Such examples include canna lilies, hardy bananas, and dahlias.

Andrew Pfeifer is the horticulture agent for the Stanly County Center of the N.C. Cooperative Extension.