The Northeast United States comprises USDA hardiness zones of 4 to 7. Perennials for these zones are cold hardy and do best in a relatively low-humidity environment. The flowers and plants that are good for these zones are ones that are easy to grow and tolerant of many weather conditions. The Northeast U.S. can grow any of the following plants without worry.
Beebalm is from the mint plant family and is botanically named Monarda didyma. It is a hummingbird and butterfly attracting perennial. Leaves will get 2 to 6 inches in length and will be fragrant if bruised. Flowers are red and 1 ½ inches in length, tubular, on stems. The entire plant will be 3 to 4 feet in height and 2 to 3 feet in width. Grow in full sun or partial shade in rich soil. Propagate via seed or clump division. It is hardy in USDA hardiness zones of 4 to 8.
Sweet Autumn Clematis
Sweet autumn clematis is from the buttercup plant family and is botanically named Clematis terniflora. It is a fragrant perennial vine. This climber reaches 30 feet long and 4 inches in width. Leaves are 2 to 3 inches in length with flowers 1 ¼ inches wide, fragrant, and star shaped. Grow in full sun with regular watering. Propagate via seed, layering, or cuttings. It is hardy in USDA hardiness zones of 5 to 10.
Aaron's beard is from the St. John's wort plant family and is botanically named Hypericum calycinum. It is a semi-evergreen perennial that is drought tolerant. This 1 foot tall plant with 2 to 4 inch long leaves will flower in yellow 2 to 4 inch wide flowers. Grow in full sun or partial shade in poor sandy soil. Propagate via softwood cuttings or rooted stems. It is hardy in USDA hardiness zones of 5 to 9.
Culver's root is from the figwort plant family and is botanically named Veronicastrum virginicum. It is a butterfly attracting perennial. Leaves are 2 to 4 inches in length on a plant that reaches 4 to 7 feet in height. Flowers are white, blue, or pink and tiny. Grow in full sun or partial shade in moist or dry soils. Propagate via seed or division. It is hardy in USDA hardiness zones of 3 to 8.