The Chicago Botanic Garden recently released results of a long-term study of spiderwort, Tradescantia.
The information in the report should be applicable to Zones 7 and 8 (Hampton Roads), but partial shade is essential in warmer areas, according to researchers. The three species that make up the complex hybrid cultivars are native to Zones 7 and 8.
Between 2005 and 2009, the botanical garden (USDA Hardiness Zone 5b, AHS Plant Heat Zone 5) evaluated 31 taxa of Tradescantia in full-sun trials. The goal of the comparative trial was to identify outstanding spiderworts for the Upper Midwest. The study concentrated on the Andersoniana Group because of their adaptability to a variety of cultural conditions.
Spiderworts are easy-care plants for full sun to partial shade. Flower production is better in full sun, but part shade is beneficial where summer temperatures are hot. Spiderworts prefer moist, well-drained soils, but do not like their roots to be overly wet or dry.
Withered petals tend to hang brown on the plant, so deadheading is recommended to improve appearance. Removing spent flowers will also reduce the chance of seedlings that may be inferior or become weedy.
Leaves tend to decline naturally after the first bloom period, or may go dormant prematurely in hot, dry weather. Providing extra moisture during the summer may slow down foliar decline. Shearing stems to the ground when foliar quality deteriorates or plants become overgrown or untidy in appearance encourages healthy new leaves later in the season. Providing supplemental water after shearing will hasten regrowth of fresh foliage. Slugs, snails, leaf spot, and foliar rust may be problems.
Foliar diseases are exacerbated by frequent overhead irrigation.
Plants were monitored regularly during the evaluation period for descriptive traits such as flower color, bloom period, plant size, and plant habit. In addition, data was collected on disease and pest problems, winter injury, and habit quality and plant health issues related to and/or affected by cultural and environmental conditions.
Twenty-six of the 31 taxa finished the five-year trial. Final performance ratings were based on flower production, habit quality (prior to and following midsummer decline), plant health, and winter hardiness.
Fourteen hardy garden spiderworts received four-star good ratings for their strong habits, good flower production, and greater resistance to fungal leaf spotting. With few exceptions, the spiderworts were fully adapted to the environmental and cultural conditions of the test garden. The majority of the cultivars closely resembled each other in habit, but they exhibited a variety of flower colors, plant sizes, and foliage colors.
The highest flower coverage, 70 percent at peak, was observed on ‘Red Cloud’, which was also the most robust of the cultivars. Additionally, good floral displays were consistently observed on ‘Blue Stone’, ‘Concord Grape’, ‘Innocence’, ‘Karminglut’, ‘Mariella’, ‘Perinne’s Pink’, ‘Snowcap’, ‘Sylvana’, ‘White Doll’, and ‘Zwanenburg Blue’. Taxa with blue-green leaves were generally less troubled by leaf spotting than green-leaved plants.
Infection levels on blue-green-leaved plants in most years were low or none but never severe; however, ‘Lord Nelson’, ‘Perinne’s Pink’, and ‘Purple Profusion’ had moderate infections in 2006 only. Winter hardiness was not a concern in the spiderwort trial. With the exception of ‘Blushing Bride’, the majority of taxa are listed hardy to at least USDA Zone 5.
Crown injury and plant loss was sporadic and insignificant overall; however, most injury was noted in 2006–07, which was the coldest winter of the trial.
A spiderwort plant is self-sterile, which means that no seed is produced unless another plant is nearby. However, when several plants are grown together they will freely produce seed. Abundant multicolored seedlings were present in the trial plots in 2007, 2008, and 2009, often growing directly out of the crown of an established spiderwort.
In fact, the proliferation of seedlings became a serious weed issue in the final years of the trial.
While the jewel-toned flowers of spiderworts are beautiful in garden borders, their slightly wild mien lends itself especially well to informal landscapes such as cottage gardens, woodlands, and waterside plantings.
Butterflies and bees frantically visit the ephemeral blossoms, making the most of the short bloom days.
In their spring and early summer glory, spiderworts are great companions to sunny garden neighbors such as geraniums (Geranium), catmints (Nepeta), bluestars (Amsonia), and grasses. In shady gardens, hostas (Hosta), astilbes (Astilbe), lungworts (Pulmonaria), and ferns are among their perfect cohorts. Planted cheek by jowl with other perennials will leave a less obvious hole when spiderworts get cut back or go dormant in midsummer.
The Chicago Botanic Garden’s Plant Evaluation Notes provide the latest information on plants suited to the Midwestern climate and growing conditions. To download a PDF of Issue 34, “A Comparative Study of Tradescantia Cultivars,” visit www.chicagobotanic.org/research/plant_evaluation.
Posted by Kathy Van Mullekom