A Comparative Study of Cultivated Asters

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.