Find Your Growing Zone
Each plant on our website lists a range of zones it will grow in. For example, if you see "6-9", this means the plant will grow in Zone 6, 7, 8 and 9.
Please Note: There are many variables involved in plant hardiness. We use generally accepted cold hardiness zone information for each plant. This does not consider microclimates created by altitude, rainfall, or directional location. In any given year, temperatures can fluctuate a full zone, up or down. Such factors as lack of snow cover, early or later extremes and protections from mulch, or buildings can also have an effect. If you have questions about plant hardiness, we encourage you to contact your local County Extension Office.
What are Growing Zones? Why are they Important?One of the most time-saving and cost-efficient tools you can use as a gardener is knowing which plant hardiness zone, also called a growing zone or climate zone, corresponds to your own back yard. Armed with this knowledge, you'll be better equipped to choose perennial plants with demonstrated hardiness in the area where you live. Although it's not a guarantee of success – after all, plants are living things subject to a host of growing challenges – it's an important first step toward choosing plants that are more likely to prosper in your climate.
Hardiness Zone Map
The USDA's Agricultural Research Service, working in tandem with Oregon State University's PRISM Climate Group, released an updated USDA Hardiness Zone Map in 2012. This map divides North American into 11 geographic zones, with Zone 1 as the coldest and Zone 11 as the warmest. Each zone is separated from the next zone by a temperature variance of 10 degrees F, and each zone is sub-divided into two parts -- "a" and "b." Within each zone, the lowest average annual temperature has been calculated, which translates to the coldest winter temperature at which plants can survive.
Different plant parts, such as the roots, stems, leaves and flower buds, have individual hardiness thresholds. This means that some perennials have above-ground parts that die to the ground during cold weather, although their roots or bulbs are still alive -- called herbaceous perennials. Some woody perennials, such as deciduous shrubs and trees, lose their leaves in cold weather but their stems and branches don't die to the ground. And evergreen trees and shrubs retain their leaves, even during winter's freezing temperatures. So a perennial that is hardy in your growing zone may be any of these plant types.
The USDA Zone Map considers only temperature as its criterion of plant hardiness, but there are other considerations, such as:
• Microclimates. Within each zone are microclimates -- temperature pockets that vary from the surrounding climate zone. For example, an enclosed courtyard garden may be warmer than the area surrounding it. Different types of soils also create microclimates by influencing the effect of frost on plants. Heavier soils, such as clay, trap and maintain heat better than light and porous sandy soils.
• Heat islands. The Urban Heat Island (UHI) effect is a result of how buildings and pavement in cities store more heat than soil and vegetation to create warmer microclimates than less-populated areas in the same growing zone.
• Elevation. The higher elevation of mountains or hills is comparable in weather terms of traveling further north. For example, in terms of plant hardiness, a plant that's hardy to Zone 7 may not be hardy if grown on a mountain or even hilly terrain in that same zone.
• Plant species vs. cultivar. Some plant cultivars have been bred specifically to have increased cold-hardiness or heat tolerance over the original plant species.
What about Growing Perennial Plants in Containers?
Plants growing in the ground are insulated by the surrounding soil, so their roots are warmer during the winter than plants that grow above ground in a pot, hanging basket or window box. A rule of thumb is to choose plants for above-ground containers that are hardy to two zones colder than where you live. For example, if you live in Zone 8, choose container plants that are hardy to Zone 6 if you want them to survive the winter.
What if I want to bring my potted patio plants indoors during the winter?
The growing zones stated are for outdoor planting. For indoor plants, and citrus trees, your growing zone does not matter. Since these growing zones are defined by "cold hardiness", and they will be indoors during the coldest months of the year, they can survive in even the coldest zones. Your plants will be fine if you bring them indoors during the winter, whether you live in Florida or Wisonsin.
Choose Your Plants!
Use these tips when deciding on new perennial plants to purchase for your yard or garden:
1. Know your zone. Discover your USDA plant hardiness zone by simply entering your zip code. Compare this zone number to nursery catalog descriptions and plant tags to see if your garden is located within the zone range of prospective plants.
2. Understand microclimates. You may be able to grow some perennials that are technically in a hardiness zone colder than where you live if the plant is in a more protected area than surrounding plants. But don't let the success of a specific plant that thrives in your garden (but isn't "supposed" to be hardy in your zone) influence your decision to buy all future plants with a zone range outside yours.
3. Compensate for container plants. Many beautiful perennials flourish year-round in containers that are elevated above the ground. If you want to leave some potted plants outside year-round without having to bring them inside during the winter, choose plants that are hardy to a zone that's two zones colder than your climate to compensate for their lack of insulation from an in-ground planting.
4. Look for cold- or heat-tolerant cultivars. Because plant breeders are continually pushing the plant-hardiness envelope by developing new cultivars within a species that have expanded hardiness zones, look for these plants as you customize your landscape design to find the "right fit" for your garden!