Although Erica carnea is listed for Zone 5a it requires a special planting technique to keep it growing for years. This is the method I used in the Zone 5 upstate area. Dig a shallow planting hole, Place a good sized flat rock a few inches in the hole flat and plant the Erica sideways with all the roots under the rock. Fill in the planting hole, covering the rock with a bit of soil if you wish. Plant foliage will turn and grow upright again shortly. The flat rock protects the roots from freezing. May be a bit of winter burn depending on snow cover but heather should recover well. This technique can be used for any perennial on the questionable edge of a growing zone.