Over a 12-year period, the Chicago Botanic Garden evaluated 26 taxa of Eutrochium species and related genera with the goal of identifying outstanding Joe-Pye weeds for Upper Midwestern gardens.

Over our 6-year trial, seven asters received five-star excellent ratings for their overall performance. Top-rated asters displayed consistently strong habits, superior flower production, excellent disease resistance, and full winter hardiness throughout a six-year evaluation term. Additionally, 19 asters received four-star good ratings for their strong performances.

From 2001 through 2009, the Chicago Botanic Garden (USDA Hardiness Zone 5b, AHS Plant Heat Zone 5) evaluated 78 Phlox taxa in full-sun trials. Download the results in this PDF.

Spiderworts may be pegged as common garden plants, but their unique flowers and strong habits mark them as uncommonly good garden plants. A kaleidoscopic palette of colors marks the ephemeral blossoms of Tradescantia cultivars. Just over half of the spiderworts in the study received four-star good ratings for their performance and ornamental qualities. As plants begin to turn shabby from decline or leaf spotting, shearing stems to the base will encourage a flush of new growth later in the season.

Throughout spring and summer the spiky flowers of Veronica rise like sentinels in the sunny garden. Speedwells can be long-lived provided that garden soils drain freely, which is especially important during winter months. A midsummer shearing after the first bloom encourages late summer flowering. Deadheading throughout the bloom cycle produces many new, spikes later in the season.

Balloonflower is a bushy, clump-forming perennial, up to 3 feet tall, with winsome buds and exuberant blossoms in midsummer. In the border or cottage garden, balloonflowers are good companions to other summer-blooming perennials and are long-lived under normal conditions.

The distinctive blossoms of bellflower (Campanula) come in hues of blue and violet, from the deepest purple to softest gray blue. Grown in full sun or light shade, bellflowers are generally easy to grow and trouble free in well-drained, alkaline soils.

Many new cultivars have renewed excitement in the Shasta daisy, including cultivars with frilly double flowers or thin curly petals. Plant in rich, well-drained soil: Shasta daisy is often considered a shortlived perennial, especially when grown in heavy or wet soils.

Equally wonderful as accents or massed in large groups, catmints are well-suited to perennial borders, herb gardens and rockeries, and can be used as ground covers, edging plants or for spilling over rock walls. True catnip, Nepeta cataria, is particularly intoxicating to feline friends, but several other common catmints also attract cats.

The wealth of meadow rues available to gardeners ensures a profusion of pretty blooms from spring into fall. These easy-to-grow plants generally prefer moist, organic soils in partial shade to full sun. Plants that become ragged after flowering can be pruned to the ground to rejuvenate plant health and encourage new growth.

Stachys' silvery leaves are perfect foils for plants with hot- or cool-colored blossoms. Conversely, betonies bring a casual formality to the border, herb garden, cottage garden or meadow. While lamb’s ears tends to decline during flowering, deadheading regenerates leaves and improves plant vigor.

Heavy-flowering Oenothera are healthy plants with winter hardiness, giving many of these taxa five-star excellent ratings. Sundrops and evening primroses thrive in full sun but tolerate light shade. Oenothera speciosa may spread rapidly to become weedy in rich or highly fertile soils.

One of the most attractive aspects of fall-blooming anemones is their extended bloom period. It is not uncommon for these plants to bloom continuously for more than two months. A great fill plant for larger landscapes, anemones can out-compete smaller herbaceous plants in close quarters.

With few exceptions, Alchemilla prove to be good garden plants. The similarity of the cultivated species -- minor differences in leaves, flowers and habits -- allows gardeners to interchange them depending on availability.

Uneven moisture regimes can make the placement of plants in the shady garden an all-or-nothing experiment. In these circumstances, a variety of dead nettles come to the rescue. From green, silver, yellow and variegated leaves to ground covers and upright habits, dead nettles offer ornamental versatility as well as a tolerance to a wide range of conditions.

Hardy geranium is a general term that is used to distinguish Geranium from its tender cousin Pelargonium, the colorful floral or bedding geranium. Many species, especially those with trailing habits, can be used on slopes, retaining walls and in containers. Several varieties can be grown together for continuous bloom from spring to autumn.

Few perennials have exploded onto the scene quite like coral bells, or Heuchera. Breeding has brought a variety of foliage shape and color and improved flower production to market. Look for coral bells with lime-green or amber-gold leaves, and abundant red or pink blossoms -- now available.

Barrenworts are tough, long-lived perennials that are an invaluable garden plant for the challenging environment of the Midwest -- their toughness and ability to compete with tree roots make them a must-have in any shade garden, and Epimedium provides a variety of unique, colorful flowers and leaves in the spring and a backdrop of green waves throughout the remainder of the year.

While many artemesias in the study proved unsuitable for northern climes, planting artemisias in lighter soils with sharp drainage may reduce the potential for winter injury or loss of these plants, and allow you to add some texture and beauty to your perennial borders and rock gardens.

Bluestars prove to be hardy, low-maintenance perennials, giving three seasons of interest in the garden. Clusters of pale blue flowers top the upright stems in May and June before new stem growth covers the remaining flowers. For exceptional floral displays, try Amsonia tabernaemontana var. salicifolia and Amsonia illustris.