Give Plants a Chance: Understanding Plant Zone Hardiness in Minnesota
Perhaps you’d love nothing more than a garden filled with orchids and hibiscus. Sadly, unless you’re planning a move to Hawaii or Puerto Rico, you may be out of luck. The good news is, thanks to our friends at the United States Department of Agriculture (USDA), we have science-based information to help us select the right plants for the right places and provide our flowering friends a blooming chance. Plant zones, also known as hardiness zones, are geographical areas defined by climate conditions, particularly minimum average annual temperature. The USDA Plant Hardiness Zone Map divides North America into 13 zones based on these temperatures. Here, we take a deep dive into how to read these maps and why it is crucial to your plantings, especially in the state of Minnesota.
Image by U.S. Department of Agriculture
Why are plant zones important?
Each zone is characterized by a range of temperatures where specific types of plants can survive and thrive. For example, plants that are well-suited to colder temperatures would be suitable for zones with lower numbers, while those that prefer warmer climates would be better suited to higher-numbered zones.
Plant Selection
Knowing your plant zone helps you choose plants that are most likely to thrive in your specific climate conditions. This can save you time, money, and effort by avoiding plants that are unlikely to survive in your area.
Gardening Success
By selecting plants appropriate for your zone, you increase the likelihood of gardening success. Plants that are well-suited to your zone are more likely to establish themselves, grow vigorously, and resist pests and diseases.
Climate Adaptation
Understanding your plant zone can also help you adapt to changing climate conditions. As climates shift over time due to factors like global warming, knowing your plant zone can help you anticipate potential changes in your local growing conditions and choose plants accordingly.
Crop Planning
For agricultural purposes, knowing the plant zone is crucial for determining which crops are suitable for cultivation in a particular area. Farmers and agricultural planners use this information to maximize productivity and optimize crop selection.
Plain and simple: plant zones provide valuable guidance for gardeners, landscapers, farmers, and anyone else involved in plant cultivation, helping them make informed decisions about plant selection and gardening practices.
Map of North Central U.S. by U.S. Department of Agriculture.
How are zones determined?
Plant zones are established based on climate data, particularly the minimum average annual temperature. The process involves several steps:
Climate Data Collection
Climate data, including temperature records, are collected from weather stations across a region or country. This data typically spans several decades to capture long-term climate patterns.
Temperature Analysis
Climatologists analyze the collected temperature data to determine the average annual minimum temperature for each location. This minimum temperature is a critical factor in determining the hardiness of plants, as it indicates the coldest conditions that plants are likely to encounter.
Zone Boundaries Definition
Once the minimum temperature data is analyzed, boundaries are defined to delineate regions with similar temperature ranges. These boundaries are typically drawn based on isotherms, lines connecting points of equal temperature.
Zone Map Creation
Using the defined boundaries, a hardiness zone map is created. This map divides the geographic area into zones, each representing a specific range of minimum temperatures. The USDA is responsible for creating and maintaining the Plant Hardiness Zone Map for North America, while similar organizations in other countries may produce their own zone maps.
Validation and Updates
The established zones are continuously monitored and validated using updated climate data. As climate patterns change over time, adjustments may be made to the zone boundaries to ensure that they accurately reflect the current climate conditions. New versions of zone maps are periodically released to incorporate these updates.
Map of Minnesota by U.S. Department of Agriculture
Growing in Minne-zone-a
Minnesota encompasses several plant hardiness zones due to its diverse climate. The state experiences a wide range of temperatures, from cold winters in the northern regions to milder conditions in the southern parts. The USDA Plant Hardiness Zone Map divides Minnesota into several zones:
Zone 3a
This zone covers the northernmost parts of Minnesota, including areas such as International Falls and Ely. It experiences very cold winters, with average minimum temperatures ranging from -40°F to -35°F (-40°C to -37.2°C).
Zone 3b
Similar to Zone 3a, Zone 3b also covers northern regions of Minnesota but with slightly milder winter temperatures. Average minimum temperatures range from -35°F to -30°F (-37.2°C to -34.4°C).
Zone 4a
This zone includes parts of central and northern Minnesota, such as Bemidji and Brainerd. Winters are cold, with average minimum temperatures ranging from -30°F to -25°F (-34.4°C to -31.7°C).
Zone 4b
Zone 4b covers additional areas in central and northern Minnesota, including cities like Duluth and Grand Rapids. Winter temperatures are still quite cold, with average minimum temperatures ranging from -25°F to -20°F (-31.7°C to -28.9°C).
Zone 5a
This zone encompasses central and southern parts of Minnesota, including the Twin Cities metropolitan area (Minneapolis and St. Paul). Winters are less severe compared to northern regions, with average minimum temperatures ranging from -20°F to -15°F (-28.9°C to -26.1°C).
Zone 5b
Zone 5b includes southern portions of Minnesota, such as Rochester and Mankato. Winters are relatively mild compared to northern regions, with average minimum temperatures ranging from -15°F to -10°F (-26.1°C to -23.3°C).
These hardiness zones help gardeners, landscapers, and farmers in Minnesota select plants that are most likely to thrive in their specific climate conditions. It's essential to choose plants that can tolerate the cold temperatures and potential frost events common in the region, especially in the northern parts of the state.
What’s my plant zone?
The USDA’s zone map has made it as simple as point-and-click to determine your location’s plant zone.
Nikki Holst, Director of Retail and Customer Experience at Copper Creek, explains that zones can over time based upon trends in temperature. For example, compared to the 2012 and 1990 maps, USDA-determined zone boundaries in the 2023 edition have shifted in many areas, including Minnesota.
Nikki Holst
Director of Retail and Customer Experience
Copper Creek Garden Center and Landscapes
“Here in the Brainerd Lakes Area, we were Zone 3b when the USDA released its previous edition in 2012; but, when updated in 2023, we are now considered Zone 4a by USDA-set standards,” Nikki explained. “This technically allows us to try some things we haven’t had in our gardens before.”
The establishment of plant zones involves a combination of climate data analysis, boundary definition, and map creation, Holst adds, all aimed at providing valuable guidance for anyone involved in plant cultivation.
So, what’s new?
With the zone change comes a new crop of opportunities for Minnesota gardeners and green thumbs. In USDA Zone 4a, which typically experiences cold winters with average minimum temperatures ranging from -30°F to -25°F (-34.4°C to -31.7°C), it's essential to choose plants that are hardy enough to withstand these chilly conditions.
Here are some types of plants that generally grow well in Zone 4a:
Perennials
Perennial plants that are well-adapted to cold climates are suitable for Zone 4a. Examples include:
- Coneflowers (Echinacea)
- Daylilies (Hemerocallis)
- Hostas
- Russian Sage (Perovskia atriplicifolia)
- Shasta Daisies (Leucanthemum × superbum)
Deciduous Trees
Many deciduous trees are suitable for Zone 4a. Look for species that are cold-hardy and can withstand frost. Some options include:
- Red Maple (Acer rubrum)
- White Birch (Betula papyrifera)
- Eastern Redbud (Cercis canadensis)
- White Spruce (Picea glauca)
Evergreen Trees
Some evergreen trees are also hardy enough for Zone 4a winters. Consider:
- Colorado Blue Spruce (Picea pungens)
- Norway Spruce (Picea abies)
- Balsam Fir (Abies balsamea)
- Eastern White Pine (Pinus strobus)
Shrubs
Cold-hardy shrubs can provide structure and visual interest to your garden. Options for Zone 4a include:
- Dwarf Korean Lilac (Syringa meyeri)
- Spirea varieties (Spiraea)
- Burning Bush (Euonymus alatus)
- Common Snowberry (Symphoricarpos albus)
Fruits and Vegetables
Certain fruits and vegetables can also be grown in Zone 4a, though you may need to select varieties that are specifically bred for cold climates or consider providing protection during the coldest months. Examples include:
- Apples (choose cold-hardy varieties like Honeycrisp or Haralson)
- Strawberries
- Carrots
- Peas
- Cabbage
When choosing plants for Zone 4a, it's crucial to consider factors such as soil drainage, sunlight exposure, and microclimates within your garden. Additionally, providing adequate winter protection, such as mulching or wrapping sensitive plants, can help them survive the cold temperatures and thrive in your garden.
So, while you may not have the orchids and hibiscus outdoors, you do have many options for beauty and color, even here in the chilly Midwest. The Copper Creek Garden Center growing experts can help suggest the best plants for your growing conditions. Just stop by and ask! We also have an excellent selection to choose from and support that lasts long after you take them home.
Planning and landscaping a wide area can be quite a task, so having a specialist guide you through the process can make a world of difference. Whether it's selecting the right plants for your environment, designing an aesthetically pleasing layout, or ensuring proper care and maintenance, having expert advice can really elevate your outdoor space. Give us a call today to schedule and appointment with a landscape specialist!
Sources: https://planthardiness.ars.usda.gov/
https://planthardiness.ars.usda.gov/pages/how-to-use-the-maps