If you're planting flowers, trees and shrubs in the greater Cleveland area, you need to know about growing zones. This area is unusual in it actually straddles three USDA zones 5b, 6a and 6b, and is in three zones on the Sunset Climate Scales--zones 39, 40 and 41. What do both of those number mean? Here's a closer look at each of them.
USDA Plant Hardiness Zone
The USDA map is the most commonly used scale, at least in the Midwest and Northeastern US. It's the one that most gardeners and nurseries use, and the one that's used by most national garden catalogs, books, magazines, other publications. This map divides North America into 11 separate zones. Each zone is 10 degrees different in an average winter than the adjacent zone. Some modifications have been made, such as sub-zones, and 6a and 6b were added.
The majority of Northeast Ohio is in zone 6a, which means the coldest the area gets is between -5 and -10 degrees Fahrenheit. The Lake Erie coastal areas (within about 5 miles of the lake) are in zone 6b, which means that the coldest temperature there is between -5 and zero degrees Fahrenheit. The low-lying areas, such as around Cuyahoga Valley National Park and the Mahoning Valley near Youngstown, are in zone 5b, which means the lowest temperatures there can reach between -10 and -15 degrees Fahrenheit.
Sunset Climate Scale
Sunset zones are based on a combination of factors: both extremes and averages of temperature (minimum, maximum, and mean), average rainfall, humidity, and overall length of growing season. Again, Northeast Ohio falls in three separate zones--39, 40 and 41. Zone 39 is 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 starts about five miles south of the lake and runs east of I-271 to Geauga, Trumbull and Ashtabula counties to the Pennsylvania border.
Growing Zones and Your Garden
What do growing zones mean to your garden? Several things. They give you an indication of when the last heavy (i.e. killing) frost will be in your area. That means that even if it's sunny in late April or early May, it's too early to plant those tomatoes, petunias or other plants that can't withstand a heavy frost. In addition, the growing zones tell you what plants will thrive in your garden. Most greenhouses and online plant retailers will indicate the growing zone range on plants they sell. If you buy from another retailer, you can check the optimal growing zone for that plant online.