Often times we are led by our preconceptions of what is beautiful and what is appropriate in using different types of plants. I would encourage you to think beyond the box and find innovative ways to use these plants that many assume would only work in "naturalistic" settings. All of the following plants, particularly if they are massed, could be used as an effective counterpoint in a formal setting.
1.Eryngium yuccifolium Rattlesnake Master
Rattlesnake master is a bold and sculptural plant with blue green foliage and pale green flowers that in one form or another persist for months. Its native range is from the Atlantic Coast to the Great Plains and south to Florida. It likes sun and well drained sites. Try it with Little Blustem, Liatris or perhaps one of the many orange Echinacea's on the market. Zone's 3-8.
Rattlesnake Master in the foreground with Little Bluestem.
2.Veronicastrum virginicum Culver's Root
The incomparable Culver's Root is an elegant understated perennial that sends up spires of white flowers in the month of June. The variety Roseum has pale pink flowers. Both Rattlesnake Master and Culver's Root are best used in mass. Considerably taller than wide I have found Culver's Root easy to grow in full sun with average moisture. 40" x 18". Zones 3-8.
The variety 'Roseum'.
The dried flowers remain intriguing during autumn.
3.Vernonia noveboracensis Ironweed
During late summer Ironweed's riveting deep magenta flowers can be found growing along moist roadside meadows from Massachusetts to Mississippi. The height is variable depending on the moisture and fertility of the soil but averages 4' high. The variety 'Iron Butterfly' is consistently shorter at 30-36". Once the flowers are past their prime the seed heads remain of interest for 2-3 months. I have had success with this plant in average to moist conditions. Zones 5-8.
4.Amsonia hubrectii Willowleaf amsonia
The spring flowers are small star shaped and fairly inconspicuous. The leaves are long and narrow and turn a brillant yellow in autumn. Shrub like at 3-3.5' high and wide it is slow to mature in its first season but takes off in it's second and third. Chanticleer Gardens in Wayne Pa. has effectively massed the plant in many of their ornamental beds. Zones 6-8.
Brillant fall color contrasts.
5.Baptisia australis False Indigo
False indigo is a long lived source of blue in late spring to early summer. Dark pods follow the flowers and decorate the foliage which remains attractive throughout the growing season. Heat and drought tolerant, I have grown False Indigo in everything from poor to outstanding soil conditions. Grows in its native range from Pennsylvania to North Carolina. 3-4' tall x 30" wide. Zones 3-8.