Plant hardiness zones

Horticulture Hints

‘Tis the season to be browsing your local greenhouses for new plants for your garden. A common mistake that a new gardener may make is that of purchasing a plant that is not suited to survive our cold Iowa winters.

To prevent winter kill and loss of perennial plants, be sure before purchasing that the tag indicates the plant is hardy for the area in which you live. This rating is called the USDA plant hardiness zone. These zones are the accumulated average winter temperatures as recorded across the country.

The plant hardiness zone map may be found at: which was last updated in 2012. This map shows our region to be in the zone 5a area, with the annual average extreme winter temperature to be between -20 to -15 degrees F.

However, when making plant selections, many experienced gardeners north of Highway 30, feel that using the previous recommendations from the 1990 map is the safer route to go. This older map listed our most of our area as being either zone 4a or 4b, with winter temperatures falling as low as -30 degrees for zone 4a.

Other plants, such as hybrid roses, may be root hardy to zone 4b, but with their top growth not being hardy to zone 5a. So experiment with a few new plants before purchasing many, as to check their winter survival in your landscape.

Did you know? Other factors that influence winter temperatures include differences between rural and urban areas and low-lying areas near streams and hilltops. These factors also affect winter temperatures when making a plant selections.

Questions? Contact McCormick at for information or advice.