A Growing zone (also called Hardiness zones) are areas that determine what plants are likely to thrive in that locations. The average winter extreme low temperature is what the USDA uses to determine growing zones. This means the USDA has collected data from hundreds of research stations across the country to determine what the lowest average temperature is in each spot every year. They then build or adjust the map of Hardiness Zones to illustrate what kinds of plants will survive the winter temperatures in each area.
This doesn’t take into consideration any abnormal extreme low temperatures. So sometimes there can be lower than average temperatures to watch out for. Luckily, natural forces aside, the USDA Hardiness Zones map is usually very accurate. When used correctly, it can be one of the most useful tools you can use to determine which plants will grow and thrive in your garden, and survive your winters and/or summers!
Finding your Growing Zone
To see an interactive and more detailed map (including a zoom function and to search by zip code) please visit the USDA’s map website: here:http://planthardiness.ars.usda.gov/phzmweb/interactivemap.aspx
Here is the current USDA Plant Hardiness Zones Map, with half-steps.
To find your zone, look for your region, state, and approximate city area. Then use the key to determine what zone the color represents. That will be your Growing Zone. For best results in your garden, only purchase and plants rated for your zone. Plants that do not mention your particular zone may not survive the average winter/summer temperatures in your area.
Growing zones that plants are rated for are usually on their tags and/or online descriptions when they’re sold. For example, if you are in Zone 4, and check a tag/description that says ‘Zones 4-8’, you can grow that plant! If the tag/description says ‘Zones 3-9’ you can grow that one, too! If the tag/description does not cover your zone, it’s not a good idea to grow that plant in your garden. We’ll talk more about that later.
Marginal Growing Zone Areas
If you are in between zones near a zone boundary line, for example where zones 3 and 4 meet you may want to be extra careful with your plantings. Being cautious and purchasing/planting for the lower-numbered (in the example’s case, zone 3) or colder zone is a good idea.
If you’d like to plant for the higher-numbered (in the example’s case, 4) or warmer zone, proceed with caution. Experiment with the knowledge that some of your plants might not ‘make it’ through the winter cold or may ‘die back’ in the summer heat.
You can also utilize a winter mulch/covering to increase your chances of winter survival. You could also use extra shade/water in summer to increase your summer survival rate. But that may not make 100% of plants tolerant of the temperatures involved.
Growing Plants Out of Your Growing Zone
If you want to try growing a plant rated higher than your particular growing zone, you can also try winter mulch and summer shade/extra water. However, your plant has a good chance of not making it. For any plant grown out of its zone, that’s normal. There is nothing wrong with that plant. It just means the plant cannot survive a place to which it cannot adapt.
We cannot recommend growing perennial plants in zones they are not rated for. If there is a plant you enjoy rated out of your growing range, consider planting it as an annual. Have the expectation it will die at the end of your growing season. But you can always replant it next year and enjoy again.
Growing Perennials as Annuals
Plenty of our customers have a great time growing their favorite perennials as annuals! Most gardeners the world over have planted annuals to brighten up their yard for just one season (or replant every year). Annual plants fill out most container gardens!
When you think of how you use plants like geraniums, petunias, impatiens, and marigolds (to name a few popular annuals in our area), know you can also use perennials out of your growing zone that way as well! Why not try some interesting perennials like penstemon, euphorbia, geum, and more in your containers and beds?
Remember, your plants will only have one season of growth. So they may not get to their full mature size, or have as profuse of blooms as they would if they had more years to accumulate growth. But the plants grown by you can still be enjoyed in the garden for what beauty they provide!