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Climate Zone Info

All About Climate Zones and Plant Hardiness

What Is Plant Hardiness?

At its most fundamental level, hardiness describes a plant's ability to endure harsh winter temperatures. Drawing upon several decades of climate data, the U.S. Department of Agriculture created the Plant Hardiness Zone Map, which breaks geographical regions into 13 climate zones (with a and b sub-zones) based on a 10-degree Fahrenheit difference in the average annual minimum temperature.

For example, a gardener in zone 5 can be reasonably sure that any plant labeled as hardy for zone 5 or colder will withstand the winter. However, the Hardiness Zone Map doesn't include fluctuations due to altitude, soil, moisture, humidity, heat, or wind, which can dramatically affect a plant's ability to survive.

Knowing your specific gardening zone is the first step in determining what plants will flourish in your gardens and that will live through the winter. So, first identify which USDA Hardiness Zone you are located in. Check out the map below and discover which seeds, bulbs, and plants work best for your region. Oh, and don't worry—there are hardy perennials and annuals eager to enhance even the coldest, most rugged terrain.

USA Climate Zone Map

Why Do We Have These Zones?

Digging deeper into climate zones means addressing the fact that hardiness to cold weather is not the only factor influencing a plant's health in your garden. You also have to consider the summer temperatures, rainfall, length of growing seasons, and humidity, which are all conveniently covered by climate zones.

While growing plants not suited to your specific environment is sometimes possible, it can be a little tricky. You see, there’s not just the question of whether or not a plant can survive in your climate, but whether or not it will thrive there. For example, some plants, such as peonies, may need a certain amount of cold weather (chilling hours) during the winter in order to set blooms. Without that, you may get a nice green plant but few or no flowers.

Generally speaking, plants typically do best as perennials (coming back year after year) in regions with climates similar to their native areas and you will have the best results with plants that are designated as appropriate for your hardiness zone.

There are five main types of climates:

  • Tropical: These zones are hot and humid, with high average temperatures and abundant precipitation.
  • Dry: These zones are hot and dry with minimal precipitation.
  • Temperate: These zones experience warm, wet summers and rainy, mild winters.
  • Continental: These zones are characterized by summers that are warm or cool and cold winters with snowstorms.
  • Polar: These climate zones are frigid in winter and relatively cold in summer.

Once you begin to understand climate zones fully, you can use them to your advantage. Gardening with climate zones in mind means only introducing plants that harmonize with specific climates. If you’re still wondering which zone you’re in, click the handy link below, and we’ll tell you, or if you’re ready to get your shop on, go ahead and click one of the additional links below to shop by your specific climate zone!

What Climate Zone Am I?

Recognizing Microclimates in Your Garden

Once you've established your climate zone, it's time to focus on possible microclimates. These are spaces on a property where the climate deviates slightly, allowing gardeners to grow plants that otherwise would be a bit too fragile for the region. Some common examples of microclimates include:

  • Full Shade: North-facing side of a home or under trees
  • Full Sun: Open fields or south-facing side of a home
  • Partial or Morning Sun: East-facing side of a home
  • Quick Drainage and Sun: Rocky hills
  • Wet and Clay: Stream or riverbeds
  • Dry and Dense Shade: Wooded forest floors

You can use the microclimates in your garden to optimize the growing conditions for your plants. For example, heat-loving plants will appreciate being next to a south-facing fence or building that will absorb and radiate the afternoon sun. Plants that need more winter chill, on the other hand, will do better on the north side of your house.

Hardy vs. Tender (or “annual”) Plants

Plants that will not survive cold winters in the ground are considered tender. Gardeners in cold-winter climates, plant tender bulbs in the spring, and when the frost hits, you can either dig them up and bring them indoors or treat them as annuals. In warmer climates, they can be planted in fall and remain in the ground until they need to be divided every few years.

  • Calla Lilies
  • Dahlias
  • Freesia
  • Caladium
  • Ranunculus

Plants that are suitable for the cold winters of the lower zones are considered cold-hardy—they die back to the ground at the end of the season but can survive in the ground until the soil warms again in the spring. Hardy plants can safely be planted in the fall. Here are a few of the plants considered cold-hardy:

  • Peonies
  • Tulips
  • Muscari
  • Hostas
  • Crocus

Gardeners in mild-winter climates who can't resist the beauty of Tulips and Crocus in the spring can simulate a cold winter by chilling the bulbs for 10–12 weeks before setting them outside in January or February.

Happy Gardening!