Plant Evaluation Notes Garden-Worthy Artemisias Richard G
Total Page:16
File Type:pdf, Size:1020Kb
Issue 19, 2003 Plant Evaluation Notes Garden-Worthy Artemisias Richard G. Hawke, Manager of Plant Evaluation Programs rtemisia, wormwood, mugwort and Artemisias come in an array of plant species are grown in gardens throughout southernwood are some of the com- habits and sizes, ranging from a few inches to USDA Hardiness Zones 3 to 8. Amon names for Artemisia,a diverse 8 feet tall, and spreading from 1 to 6 feet wide. Artemisias are commonly used as genus of herbaceous and shrubby species from Stems can be woody or herbaceous, clumping accents, foils or fillers in gardens and a variety of climatic regions around the world. or rhizomatous with habits that are upright, containers. The silvery foliage is invaluable Artemisia includes garden perennials, such as bushy, low-mounded or ground-hugging. for cooling down harsh colors, and can be used white sage (Artemisia ludoviciana) and Artemisia leaves are typically dissected, gray to complement or contrast with the flowers absinthe (Artemisia absinthium), the culinary or white, hairy and aromatic, although some and foliage of adjacent plants. The soft, ferny herb tarragon (Artemisia dracunculus) and a species have green leaves. The scented foliage leaves of Artemisia absinthium ‘Lambrook symbol of the Old West, sagebrush (Artemisia is considered a repellent to insects, rabbits and Silver’ or A. ‘Powis Castle’ are a striking tridentata). Gardeners are familiar with the deer. The small, gray to white discoid flowers, textural contrast with bolder leaves of other silver artemisias that are commonly grown as which are produced in clusters during summer perennials. Various flower colors, including foliage plants for texture and color, but there and fall, lack the large or colorful ray florets so blue, pink, purple or yellow, mix well with the are also artemisias with green leaves and identifiable to the aster family. bright silver leaves of A. ludoviciana ‘Valerie attractive floral displays. Many species are native to arid or Finnis’ and A. ludoviciana ‘Silver Queen’. The Artemisia contains about 300 annual, Mediterranean-like climates and are aptly creamy white blossoms of A. lactiflora are a biennial or perennial herbs and woody shrubs suited to sunny, dry infertile gardens. Hence, graceful presence in the back of the border and from the temperate Northern Hemisphere, these species are not always well suited to combine well with other late-season flowers. western South America and South Africa. soils that retain moisture during the winter Artemisias are suitable for perennial borders, Artemisia is a member of the aster family months or to climates with high summer herb gardens, containers and rock gardens, and (Asteraceae) and is closely related to other humidity. Excessive moisture can result in root are also used as edging plants. Gardeners who garden perennials such as yarrow (Achillea), rot during dormant periods and crown melt- provide the right cultural conditions can take golden marguerite (Anthemis) and tansy out during summer months. The silvery-leaved advantage of the variety of plant habits, foliage (Tanacetum). The composite flowers of most artemisias are best grown in full sun in well- colors and foliage textures that make artemisias are not regarded as ornamental, and drained to dry soils with low fertility. artemisias outstanding garden perennials. Conversely, green-leaved species can tolerate these plants are grown instead for their The Evaluation Project more soil moisture and are easily adapted to aromatic, gray- to silvery-green leaves. White The Chicago Botanic Garden (USDA average garden conditions. Fertilization is not mugwort, Artemisia lactiflora, is a green- Hardiness Zone 5b, AHS Plant Heat-Zone 5) required and high nitrogen can cause tall, leaved exception grown for the clusters of completed a four-year comparative study of floppy stems especially on the silver-leaved creamy white flowers borne at the tops of tall Artemisia in 1996. The project goal was to species. Many of the cultivated perennial stems. observe the ornamental characteristics, winter hardiness and cultural requirements of 26 species, cultivars and garden hybrids of Artemisia, and to determine the best artemisias for Midwest gardens. The trial included commercially available artemisias as well as species obtained from seed exchanges with European botanic gardens. Nomenclature follows The New Royal Horticultural Society Dictionary of Gardening and the RHS Plant Finder. The following synonyms are commonly found in reference literature and Richard Hawke/Sticky Wicket, Dorset, England Wicket, Richard Hawke/Sticky gardening publications: A. ‘Huntington’ = A. absinthium ‘Huntington Gardens’; A. absinthium ‘Silver Frost’ = A. ludoviciana ‘Silver Frost’; A. alba = A. camphorata; A. ‘Powis Castle’ = A. arborescens ‘Powis Castle’; A. ludoviciana ‘Silver Queen’ = A. Artemisia absinthium ‘Lambrook Silver’ 2 Plant Evaluation Notes Chicago Botanic Garden ludoviciana var. albula ‘Silver Queen’; A. pur- completed the study are shown in Table 1. A rabbit damage. Winter injury due to wet soil shiana = A. ludoviciana; and A. schmidtiana summary rating was assigned to each plant conditions and/or cold temperatures was ‘Silver Mound’ = A. schmidtiana ‘Nana’. based on plant habit and health, cultural observed on a number of taxa. The evaluation site received approxi- adaptability and winter injury. A four-star The artemisias typically grew well for mately 10 hours of full sun during the growing rating signifies a good performance, whereas a most of the summer and were not generally season and was openly exposed to wind in all one-star rating indicates a very poor afflicted with serious health issues. Melt-out, directions. The well-drained clay-loam soil performance. or the rotting of a portion of the crown, was a was amended with composted leaves and had a Plants that died during the evaluation trial periodic problem associated with heavy rain pH of 7.4 throughout the evaluation term. Turf were not routinely retested and are not listed in and subsequent high humidity. The stems of grass pathways surrounded the beds on all Table 1. Artemisia ‘Huntington’, A. ‘Mrs. G. many artemisias declined in early August sides; and the plots, each comprised of 15 Reed’, A. ‘Powis Castle’ and A. arborescens because of the season’s heat, humidity and plants, were separated within the beds by ‘Porquerolles’ died during the first winter, but rain. The taxa that experienced melt-out mulched strips. only ‘Powis Castle’ and ‘Porquerolles’ were damage in one or more years were Artemisia Maintenance practices were kept to a replanted for continued evaluation. Since a absinthium, A. absinthium ‘Lambrook Silver’, minimum to simulate home garden culture. one-year trial was considered inconclusive, no A. frigida, A. ludoviciana ‘Silver Queen’, Water was provided as needed, and no determination was made regarding the winter A. sericea, A. schmidtiana ‘Silver Mound’, fertilizer was applied. Faded flowers and hardiness of the two taxa that were not A. stelleriana and A. stelleriana ‘Silver lodged stems were not routinely removed or retested. Artemisia capillaris, A. integrifolia, Brocade’. Stem regeneration usually began cut back. In 1995 and 1996, all plants were cut A. laciniata and A. selengensis were removed within a few weeks of damage. Rabbits were back to the ground after flowering to after two years due to lack of ornamental an occasional pest to A. lactiflora and rejuvenate health and habits. Mulch qualities and a weedy nature. These four taxa A. lactiflora ‘Guizhou’. In 1994, severe consisting of shredded leaves and wood chips were grown from seed obtained from damage to A. lactiflora resulted in approxi- was placed between the plots for weed European seed exchange programs. mately 75% of stem loss over the entire plot. suppression and aesthetic purposes. Hemlock Six of the 26 taxa received the highest Many of the issues related to the decline boughs were placed over the plants in early performance ratings based on superior in habit quality were associated with the onset November to shed water off the crowns of the ornamental characteristics, good health and of flowering. A general decline in plant health plants during the winter months. habits, and winter hardiness. Among the best during and/or following flowering resulted in plants were Artemisia absinthium ‘Lambrook open crowns, floppy to lodged stems and Observations Silver’, A. alba, A. lactiflora, A. lactiflora leafless lower stems. Open crowns and fallen The 26 taxa of Artemisia were observed ‘Guizhou’, A. ludoviciana ‘Valerie Finnis’and stems were observed on most taxa in late for winter hardiness, cultural adaptability to A. schmidtiana ‘Silver Mound’. These plants, summer to early fall, coinciding with or the soils and conditions of the evaluation site, however, were not necessarily exempt from following the flowering period. In all cases, disease and pest problems, and ornamental the health and habit issues that affected other new growth began after flowering was attributes including foliage and habit quality, taxa. The problems related to health and habit completed, whether or not stems were cut plant size, floral display and spreading quality included crown melt-out caused by back, and many taxa quickly rebounded to potential. Eighteen of the 26 taxa survived all high humidity and/or wet soils; open crowns; improved health by the end of the season. Taxa four years of the study. Plant traits and floppy to lodged stems; bare lower stems; with open habits and floppy stems in early evaluation information for the taxa that general decline due to flowering stress; and summer, prior to flower bud development, Table 1: Plant Characteristics and Performance Summary Ratings Overall Artemisia Height Width Foliage Winter Bloom Period Flower Ornamental Rating Color Injury Coverage Floral Display1 ★ ‘Silverado’ 24 in. spreading silver yes mid Aug-early Oct 60-80% yes ★★ absinthium 50 in. 30 in. silver-green yes mid Jul-mid Aug 40-60% no ★★ absinthium ‘Silver Frost’ 24 in. 32 in. silver yes mid Aug-mid Sept 40-60% no ★★★★ absinthium ‘Lambrook Silver’ 40 in. 27 in.