Exceptional Perennials

If you find it challenging to decide which plants to choose, consider trying a perennial plant of the year.

In 1990, the Perennial Plant Association, a trade group, began an annual program to showcase exceptional perennials. The criteria for consideration include plants suitable for a wide range of growing climates, those requiring low maintenance, and those having multi-seasonal interest. While these outstanding plants vary in bloom time and color, size, form, and preferred growing site, they are all easy to grow and generally trouble-free. Below are winners from the past ten years.

2024 Phlox paniculata 'Jeana'

Garden Phlox

Named for Jeana Pruitt, who discovered it growing along the Harpeth River near Nashville, Tennessee, this garden phlox variety stood out for its mildew-free foliage. It is hardy in USDA Plant Hardiness Zones 4 to 8 and prefers full sun to part shade. Growing up to 5 feet tall, it has a clumping, upright habit and blooms from mid-July through early September. 'Jeana' has tubular pink flowers that are densely packed in large, cone-shaped, terminal clusters that grow up to 6 inches long. Each individual flower, called a pip, has a long corolla tube and flat petal-like lobes that are much smaller than the flowers of other garden phlox. Its high resistance to powdery mildew can keep this hardy, easy-to-grow, sun-loving pollinator magnet beautiful all season long.

2023 Rudbeckia ‘American Gold Rush’

Black-eyed Susan

Figure 2. Rudbeckia 'American Gold Rush' by the Penn State Flower Trials.

This low-maintenance, easy-to-grow black-eyed Susan hybrid is hardy in Zones 4 to 9 and will grow best in full sun, but can tolerate partial shade. It is blanketed with yellow-gold, 3-inch flowers with arching petals surrounding cone-shaped, black-brown centers. It has a naturally dome-like, compact form that does not require pinching to shape and grows 22 to 27 inches tall and 40 inches wide. It has 2-inch-wide leaves, which are thinner than many other cultivars, and both its leaves and stems are covered in fine hairs, giving the foliage a silvery cast.  Many black-eyed Susan varieties are often plagued by the fungal disease septoria leaf spot caused by the fungus Septoria rudbeckiae, but the thin, hairy foliage of 'American Gold Rush' provides resistance to the disease. 'American Gold Rush' is a beautiful plant for many settings. It can create a stunning display in a perennial bed or border, bring a bright splash of color to a native planting, or provide an excellent addition to a cutting garden.

2022 Schizachyrium scoparium

Little Bluestem

Figure 3.  Little bluestem (Schizachyrium scoparium) by Patti Schildkamp, Penn State Master Gardener.

Little Bluestem is a warm-season ornamental grass that requires little care and is drought-tolerant. Hardy in Zones 3 to 9, it thrives in full sun and poor soil and grows most rapidly on the hottest summer days. It begins growing in late spring and, on average, grows 1 to 3 feet tall, but height will vary with variety. Its leaves are green or blue-green, long, thin blades with parallel veins. A bluish color at the base of the stems gives it its name. In late summer, branched flower stalks emerge, growing to a height above the leaves. Some of these flower stalks reach 5 feet. Flowers are arranged in a cluster called a spike, which is 1 to 3 inches long and may be purple to bronze in color. Flowers are followed by a show of fluffy, silvery-white seed heads. Frost accents the plants with a reddish tint, providing winter interest. Their deep fibrous root systems, which can extend 5 feet into the ground and laterally through upper soil, allow them to withstand drought and make it an ideal plant for erosion control. Along with beautifying your yard, Little Bluestem provides cover for ground birds and small mammals, its seeds provide food for songbirds and upland game birds, like grouse and pheasant, and it is a larval host plant for a variety of Skipper caterpillars.

2021 Clinopodium nepeta subsp. nepeta

Calamint

Figure 4. Clinopodium nepeta courtesy of Missouri Botanical Gardens.

This perennial, native to the Mediterranean, is hardy in Zones 5 to 7 and will grow 12 to 18 inches tall and 12 to 24 inches wide. It prefers full sun and will tolerate drought and poor soil. A vigorous performer, it is spread by rhizomes or self-seeding and will form a dense, spreading foliage mat of gray-green, oval leaves that have a minty lemon scent when crushed. Long blooming, its loose clusters of pink, white, or lavender tubular flowers bloom from June until frost. Subps. nepeta has slightly larger flower clusters with up to 20 flowers in each and slightly larger flowers than other nepeta species. Calamint can make an informal ground cover, be used as an edging plant for walks or borders, or be allowed to sprawl over containers or walls.

2020 Aralia cordata 'Sun King'

Japanese Spikenard          

Figure 5. Aralia cordata 'Sun King' courtesy of Walters Gardens.

Perfect for a shade garden, this deciduous perennial can be grown in full to part shade. It is hardy in Zones 3 to 9 and will grow 3 feet tall and 3 feet wide. As it emerges mid-spring, the plant quickly forms large clumps of golden-yellow leaves on reddish-brown stems. The leaves will be more lime green than yellow when grown in full shade. From July to September, tiny white flowers appear on short stalks, forming loose, spike-like clusters atop 2-foot stems. Attractive to birds, purplish-black, inedible berries follow the flowers and will ripen in the fall. This unique perennial is an excellent companion to hosta and other woodland perennials.

2019 Stachys monieri 'Hummelo'

Betony

Figure 6. Stachys 'Hummelo' is in the foreground in a demonstration garden. Mandy L. Smith, Penn State.

Native to Europe and Asia, this perennial prefers full sun to part shade. Hardy in Zones 4 to 8, it will grow 18 to 24 inches tall and wide. It forms large, matted clumps of long, narrow, glossy, green, textured leaves. A member of the mint family (Lamiaceae), it is spread by runners. While it is not as aggressive as some types of mint, over time, the clumps will form a dense ground cover. In summer, rose-lavender, two-lipped, three-lobed flowers appear on leafless spikes that rise above the foliage. Deadheading spent flower spikes will help encourage reblooming. This perennial is attractive to pollinators and a great addition to a sunny border.

2018 Allium 'Millenium'

Ornamental Onion

Figure 7. Allium 'Millenium' by Mandy L. Smith, Penn State.

This hybrid, ornamental onion prefers full sun and is hardy in Zones 4 to 9. Upright clumps of grass-like, 6 to12 inch deep-green leaves form in the spring. When crushed, the leaves have an onion-like smell and tend to be avoided by deer and rabbits. By midsummer, later than many other alliums, two or three sturdy flower stalks rise above the foliage, and each produces a single 2-inch globe of rose-purple florets that last for about four weeks. Many alliums are unwanted because of their reseeding behavior. 'Millenium' has the advantage of being less fertile, and it produces 50% fewer seeds, but if self-seeding is not wanted, it should still be deadheaded. Heat tolerant, this easy-to-grow perennial is a great accent for mixed borders and beds and is a pollinator magnet.

2017 Asclepias tuberosa

Butterfly Weed

Figure 8. Butterfly milkweed or butterfly weed (Asclepias tuberosa) by Mandy L. Smith, Penn State.

This native perennial in the milkweed family (Apocynaceae) is hardy in Zones 3 to 9. It prefers full sun and will grow well in poor, dry soil. Spiraling, narrow leaves form upright clumps that will grow 1 to 3 feet tall and wide. Flat, slightly dome-shaped, 2- to 5-inch-wide clusters of bright orange to yellow-orange, star-shaped flowers bloom in mid-summer through early fall. Deadheading the flowers will stimulate another bloom cycle. The flowers are followed by 3- to 6-inch-long seed pods full of silky-tailed seeds. It grows deep, tuberous, and tap roots that do not transplant well, so it is best left undisturbed once it has been established. However, it will grow easily from seeds. Providing a good source of pollen and nectar for many pollinating insects as well as being a larval host plant for the monarch butterfly, butterfly weed can be a great addition to a pollinator garden or a companion to native ornamental grasses, asters, and purple coneflowers to create a butterfly habitat.

2016 Anemone x hybrida 'Honorine Jobert'

Windflower

Figure 9. Anemone x hybrida 'Honorine Jobert' by Mandy L. Smith, Penn State.

This Japanese anemone hybrid cultivar has a mounded, compact habit. Hardy in Zones 4 to 8, it will grow in full sun to part shade, prefers well-drained soil, and does not tolerate wet soil in the winter. Dense, compact mounds of glossy, dark-green, trifoliate leaves reach only 12 to 18 inches tall, but once in bloom, the plants will reach 3 to 4 feet.  Blooming in late summer into fall, clusters of bright, white flowers with green centers surrounded by a corolla of yellow stamens are held on long, thin, graceful stems. This easy-to-care-for, late-blooming perennial has no insect pests or disease problems and is not prone to deer browsing. This anemone’s bright white flowers can contrast beautifully with other fall garden colors.

2015 Geranium x cantabrigiense 'Biokovo'

Cranesville Geranium

Figure 10. Geranium x cantabrigiense 'Biokovo' by Mandy L. Smith, Penn State.

Semi-evergreen and hardy in Zones 5 to 8, this cranesbill geranium variety prefers full sun to part shade but will tolerate full shade. It will grow 6 to 12 inches tall and 12 to 18 inches wide and prefers well-drained soil. Spread by runners, aromatic, seven-lobed, glossy light green leaves create a low, spreading mat that turns red in the fall for year-round interest. Masses of five-petaled, white flowers, tinged with pink at the base of each petal surrounding pink stamens, bloom from May to June. 'Biolovo' is a great choice for an edging plant or can be used to create a beautiful ground cover.