|
 Photos courtesy of Chicago Botanic Garden
Gardeners are very good at categorizing plants by flower color, plant size, garden usefulness or any number of other delineations. They further rank plants in a hierarchy of garden-worthiness ranging from rare or must-have to tried-and-true or common. Where a plant falls on that continuum is subjective since gardening is a personal endeavor. For instance, Tradescantia, or spiderworts, are often cited as common garden plants, but are they in truth commonly grown? Spiderworts seem to be grown less than the wide selection of available cultivars would imply. While their distinctive flowers and lush foliage are undoubtedly appealing to many gardeners, perhaps their midsummer unruliness keeps other gardeners at bay.
A lot to offer
Despite the fact that Tradescantia is in the predominantly tropical dayflower family, spiderworts are indigenous to most of the continental United States, with species variously adapted to full sun, deep shade, high or low temperatures and xeric habitats.
A kaleidoscopic palette of colors — sumptuous blues, rich purples, lush violets, vibrant pinks and brilliant whites — mark the ephemeral blossoms of spiderworts.
Flowers last for one day only; hence, the origin of the common name dayflower.
Flowers are actually open for less than a day, since the delicate petals curl up by afternoon as the heat of the day rises.
Flowers may remain open longer on cool or cloudy days or when grown in shade.
Another common name, trinity flower, hints at the tripartite composition of the flower — three sepals, three petals and six stamens.
Up close, the whimsical flowers are vaguely Seuss-like in appearance. Bright yellow anthers sit atop fuzzy filaments within the center of the broadly triangular petals. The 2- to 3-inch tricorne flowers are clustered in terminal umbels, with buds opening daily over several weeks in late spring and early summer. Flowering stalls as summer enters its dog days; in fact, the entire plant may go dormant after the first flower cycle. Flowering resumes sporadically in the cool latter days of summer and early autumn. A single spiderwort plant is self-sterile, which means that on its own it will not produce seed.
However, when two or more plants are grown together, an abundance of seed is ensured. Plants resulting from this seed will probably not look like the parents.
Although spiderworts are free-flowering, there always seems to be more plant than flower. The slightly fleshy, strap-shaped leaves come in shades of green but may be blue-green, chartreuse or yellow. Spiderworts form dense, fairly wide-spreading clumps with upright to arching succulent stems to 24 inches tall. The common name, spiderwort, refers likely to the mucilaginous secretion exuded from cut or broken stems, which hardens into web-like threads. The Andersoniana Group closely resembles each other in habit but offers a variety of flower color, plant size and foliage color.
In the landscape
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. Garden spiderworts are winter hardy in USDA Hardiness Zones 4-9.
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.
In their spring and early summer glory, spiderworts are great companions to sunny garden neighbors such as geraniums, catmints, bluestars and grasses. In shady gardens, hostas, astilbes, lungworts and ferns are among their perfect cohorts.
The evaluation study
Between 2005 and 2009, the Chicago Botanic Garden (USDA Hardiness Zone 5b) evaluated 31 taxa of Tradescantia in full-sun trials.
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, habit quality and plant health issues related to and/or affected by cultural and environmental conditions.
Fourteen hardy garden spiderworts received four-star good ratings for their strong habits, good flower production and greater resistance to fungal leaf spotting. Some of those include ‘Angel Eyes,’ ‘Bilberry Ice,’ ‘Perinne’s Pink,’ ‘Therese’ and ‘Zwanenburg Blue.’
By standard measures of flower production, spiderworts would not be considered exceptionally strong bloomers. The highest flower coverage, 70 percent at peak, was observed on ‘Red Cloud,’ which was also the most robust of the cultivars.
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.
Foliar disease, midsummer decline in health and reseeding were the primary challenges to growing spiderworts in the trial. The mono-cultural nature of a comparative trial contributes unnaturally to increased levels of a particular disease such as fungal leaf spot of Tradescantia. In a typical garden setting where fewer plants of one type are grown, it is likely that disease levels would be greatly reduced. Recommendations to prevent or minimize fungal diseases include selecting disease-resistant plants, eliminating overhead watering and removing all diseased plant parts when they occur or at the end of the season.
Final notes
The natural decline of spiderworts after flowering can cause consternation for some gardeners. Growing spiderworts in light shade and supplying adequate water throughout the growing season may hold off the onset of foliar decline. 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.
An additional benefit to removing withered stems and spent flowers is that reseeding will be reduced, thereby decreasing the potential weediness of spiderworts. Spiderworts are useful in a variety of garden settings, particularly in landscapes such as cottage gardens, woodland edges and meadow plantings. Understanding their nature will ensure that gardeners know how to deal with them come midsummer. Spiderworts may be pegged as common garden plants, but their unique flowers and strong habits mark them as uncommonly good garden plants.
Richard G. Hawke is plant evaluation manager at the Chicago Botanic Garden, rhawke@chicagobotanic.org.
|
