Ohio's fertile soil and warm summer temperatures make the state ideal for farming and gardening. If you want to plant flowers, trees, vegetables, and shrubs in your yard, it's helpful to know your area's hardiness zones. There are two standard hardiness zone maps used in the United States—one created by the United States Department of Agriculture (USDA), and the other by Sunset magazine (a popular lifestyle publication).
USDA Plant Hardiness Zones
The USDA map is the most commonly used hardiness zone scale. Seed companies, national garden catalogs, and farming magazines reference the USDA zones. Unless another scale is specified, the mention of hardiness zones usually refers to the USDA scale. The map divides North America into 13 separate zones that delineate annual extreme minimum temperatures, separated by 5-degree increments. The map was first created in 1927 by Alfred Rehder. In 2012, the USDA made the most recent update using weather records from 1976–2005.
Ohio USDA Hardiness Zones
The three USDA zones found in Ohio are 5b, 6a, and 6b. The majority of the state falls under zone 6a, with low temperatures bottoming out between minus 5 and minus 10 F. Low-lying regions like Cuyahoga Valley National Park are designated as zone 5b and are the coldest spots in the state with temperatures reaching minus 15 F. Some places around the Lake Erie coast and a few southern locations near the Ohio River are assigned to zone 6b—these areas experience slightly higher winter temperatures that drop to minus 5 F.
Sunset Climate Scale
Sunset hardiness zones are based on a combination of factors: temperature extremes and averages (minimum, maximum, and mean), average rainfall, humidity, and overall length of the growing season. The map divides Ohio into three Sunset climate zones: 39, 40, and 41.
Sunset zone 39 encompasses the Lake Erie coastal regions, all the way around the lake. Zone 40 starts about five miles south of the lake, goes east to about I-271 and west to the Indiana border. Zone 41 also begins about five miles south of the lake and runs east of I-271 to Geauga, Trumbull, and Ashtabula counties to the Pennsylvania border.
Hardiness Zones and Your Garden
When it comes to your garden, hardiness zones give you an indication of when the last hard frost will be in your area. Even if it's sunny in late April or early May, it's too soon to grow tomatoes, petunias, or other frost-sensitive plants. Hardiness zones tell you what plants will thrive in your garden. If you're unable to locate the growing zone for a specific plant, you can search Gardenia.net, to find out the appropriate zones.
Many vegetables including radishes, beets, parsnips, cucumbers, cauliflower, carrots, and lettuce grow well in Ohio during the summer season. If planting flowers, native perennials (you only need to plant them once) like purple coneflower, allium, and black-eyed Susans are hardy and require little maintenance. If you'd like to learn more about native species, the Ohio Department of Natural Resources has a thorough list of Ohio native plants organized by habitat.