The United States Department of Agriculture (USDA) designates planting zones based on an area's minimum winter temperature. Planting zones 5 and 6 make up the majority of Pennsylvania. These zones are further divided into sub-zones 5a, 5b, 6a and 6b.
Pennsylvania spans planting zones 5 and 6, according to the United States National Arboretum. Zone 5, which spans from central to northwestern Pennsylvania, features minimum temperatures ranging from minus 20 to minus 10 degrees Fahrenheit. Zone 6 covers the majority of eastern and southern Pennsylvania with minimum temperatures between minus 10 and zero degrees Fahrenheit.
According to the National Garden Association, the Mid-Atlantic region, including Pennsylvania, is influenced by both coastal weather and the Great Lakes. Cold temperatures from the Great Lakes and Ohio River Valley influence the planting zones by providing a reliable snow cover during most winters. Coastal storms, including hurricanes and nor'easters, contribute to the average precipitation of 35 to 40 inches each year. These climate factors are important reasons why the USDA assigned Pennsylvania to planting zones 5 and 6.
According to the National Gardening Association, the mid-Atlantic climate, including Pennsylvania, is an ideal place to plant shrubs and trees. Gardeners can locate other plants recommended for zones 5 and 6 by consulting local nurseries. The Nature Hills Nursery, for example, recommends many perennial flowers for Pennsylvania's planting zones, including black-eyed Susans, clematis, columbine, daylilies, foxglove and phlox.
- Photo Credit foxglove image by david purday from Fotolia.com
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