ISSUE 28, 2007 Evaluation Notes An Evaluation Report of Meadow Rues Richard G. Hawke, Plant Evaluation Manager

he merits of meadow rues is a member of the butter- some meadow rues a decidedly fernlike (Thalictrum)—their delicate flow- cup family (), which appearance. Leaflet shape and color Ters, handsome foliage and graceful includes other important garden perenni- varies as well, being round, oval or linear habits—are treasured by many gardeners. als such as Aquilegia, Delphinium and and blue-green, gray-green or green. From the diminutive T. kiusianum to the Helleborus. Many of the 130 worldwide Meadow rues have small flowers that titanic T. pubescens, they possess a dis- of Thalictrum are indigenous to feature clusters of but lack true tinctive charm. Meadow rues are a northern temperate zones. Meadow rues petals. In some species, colorful and per- diverse group of perennials well-suited to are perennial herbs with clump-forming sistent petaloid subtend the sta- a variety of garden settings including or rhizomatous habits ranging from sever- sunny borders, woodlands and rockeries. al inches to over 10 feet tall. Their fine- The wealth of meadow rues available to textured leaflets are arranged pinnately THE WEALTH OF MEADOW gardeners ensures a profusion of pretty (featherlike) or ternately (divided one or blossoms from spring into fall. more times into groups of three), giving RUES AVAILABLE TO GARDENERS ENSURES A PROFUSION OF PRETTY BLOSSOMS FROM SPRING INTO FALL.

mens; whereas, other species have insignificant sepals that may fall off early, leaving only the stamens to provide the floral display. For example, the pendulous flowers of Thalictrum rochebruneanum have conspicuous lavender sepals sur- rounding a boss of primrose-yellow sta- mens, while the flowers of T. aquilegiifoli- um are fuzzy pompons of lilac-colored sta- mens only. The yellow, pink, violet, white or greenish flowers are borne in ter- minal or axillary clusters in late spring and summer. Columbine meadow rue (T.

Photographed in the garden of Linda Cochran, Bainbridge Island, WA by Richard Hawke Richard by WA Bainbridge Island, of Linda Cochran, in the garden Photographed aquilegiifolium) is the first to bloom in mid-May, while ‘Elin’ and T. roche- bruneanum have flowers lasting late into the summer and early autumn. The easy-to-grow meadow rues gen- erally prefer moist, organic soils in partial shade to full sun. In some cases, such as Thalictrum aquilegiifolium, consistent moisture is beneficial for success in sunny gardens. that become ragged after flowering can be pruned to the ground to rejuvenate plant health and encourage new growth. Meadow rues are generally trouble-free, although powdery mildew and miners are occasional pest prob- lems for some species. Thalictrum rochebruneanum 2 Plant Evaluation Notes CHICAGO BOTANIC GARDEN

Meadow rues are used formally or tions as well as two additional species display and leaf color; cultural adaptabili- informally in borders, meadows and collected in Russia. The goal of the com- ty to the soil and environmental condi- woodland gardens. As a rule, tall meadow parative trials was to identify outstanding tions of the test site; disease and pest rues are best at the back of the border, but Thalictrum for full-sun gardens through an problems; and winter injury. Final ratings the statuesque, yet airy Thalictrum roche- assessment of their ornamental traits, are based on flower production, plant bruneanum has a see-through quality that disease and pest resistance, cultural health, habit quality and winter hardi- makes it a good accent in the midborder adaptability and winter hardiness. ness. Plant traits, evaluation specifics and too. Small species such as T. kiusianum Eight plants of each taxon were final ratings for 17 commercially available and T. ichangense may be overwhelmed by grown in side-by-side plots for easy com- taxa that completed the trial are noted in neighboring plants in the perennial bor- parison. The evaluation site received Table 1. Three accessions of Thalictrum der but are well-suited to rock gardens. approximately 10 hours of full sun during delavayi ‘Hewitt’s Double’ were evaluated Pairing the fine-textured meadow rues the growing season and was openly between 1998 and 2001 but each time all with bold-leaved perennials such as exposed to wind in all directions. The the plants died after one season in the rodgersias (Rodgersia) and ligularias well-drained, clay-loam soil was amended trial; therefore, the evaluation of this (Ligularia) creates a dramatic contrast. In with composted and had a pH of taxon was considered incomplete and not full sun, meadow rues combine nicely 7.4 throughout the evaluation term. included in Table 1. Performance infor- with daylilies (Hemerocallis), phloxes mation on wild-collected taxa is high- (Phlox) and ornamental grasses; while yel- Maintenance practices were kept to lighted in the sidebar on page 6; these low waxbells (Kirengeshoma), turtleheads a minimum to simulate home garden cul- taxa were not rated because they are not (Chelone) and ferns make delightful com- ture. Water was provided as needed and recommended for garden use. panions in shady gardens. no fertilizer was applied. Plants were not routinely cut back after flowering, but In general, the meadow rues exhibit- ed strong habits and good flower produc- The Evaluation Study occasionally stems were pruned to the tion in the full-sun test site. The lack of The Chicago Botanic Garden ground to rejuvenate foliage and plant any serious pest or disease problems, com- (USDA Hardiness Zone 5b, AHS Plant health. Mulch consisting of shredded bined with winter hardiness, contributed Heat-Zone 5) evaluated 26 taxa of leaves and wood chips was placed around to high ratings for many plants. Eleven Thalictrum in two successive trials from the plants for water conservation and taxa received four-star good ratings for 1995 through 2003. The first trial, from weed suppression. No winter protection their overall performance, including 1995 through 1999, included six species was provided. ssp. glaucum, T. flavum that were wild-collected in different ‘Illuminator’, T. kiusianum, T. lucidum, regions of Russia. The second trial took Observations T. minus ‘Adiantifolium’, T. pubescens, place from 1998 through 2003 and con- The comprehensive evaluation of Thalictrum T. rochebruneanum, T. rochebruneanum tained 18 cultivated taxa obtained from included the collection of data ‘Lavender Mist’, T. rochebruneanum ‘Purple commercial sources or botanical institu- on ornamental traits including floral

Table 1: Plant Characteristics and Performance Summary Ratings Overall Thalictrum Flower Color Flower Bloom Period Flower Leaf Color2 Plant Plant Rating Size Coverage1 Height Width

1 HHHH ‘Elin’ lavender, yellow ⁄2 in. late Jun-mid Aug good purple/blue-green 96 in. 42 in. 3 HH actaeifolium lavender and white• ⁄8 in. Aug-Sep poor bronze/green 34 in. 22 in. 5 HHH aquilegiifolium pale lavender• ⁄8 in. late May-late Jun fair blue-green 30 in. 20 in. HHHH aquilegiifolium ‘Purpureum’ lavender• 1 in. mid May-late Jun good blue-green 42 in. 20 in. 3 HHH aquilegiifolium var. album white• ⁄4 in. mid May-mid Jun fair blue-green 33 in. 16 in. 1 HH delavayi lavender, yellow ⁄2 in. early to late Jul poor green 33 in. 14 in. 1 HHHH flavum ‘Illuminator’ yellow• ⁄2 in. late Jun-late Jul fair yellow/blue-green 49 in. 28 in. 1 HHHH flavum ssp. glaucum yellow• ⁄2 in. mid Jun-late Jul good blue-green 72 in. 30 in. 1 HHH flavum ssp. glaucum ‘True Blue’ yellow• ⁄2 in. early Jul-early Aug good blue-green 50 in. 26 in. 1 HH ichangense pale lavender• ⁄2 in. early Jun-early Jul poor bronze/green 10 in. 18 in. 1 HHHH kiusianum pink• ⁄2 in. late Jun-mid Aug excellent purple/green 5 in. 15 in. 1 HHHH lucidum pale yellow• ⁄2 in. late Jun-early Aug excellent green 72 in. 30 in. 1 HHHH minus ‘Adiantifolium’ yellow• ⁄2 in. mid Jun-late Jul excellent blue-green 61 in. 24 in. 1 HHHH pubescens creamy white• ⁄2 in. late Jun-early Aug excellent green 120 in. 45 in. 1 HHHH rochebruneanum lavender, yellow ⁄2 in. early Jul-Sep good purple/blue-green 72 in. 30 in. 1 HHHH rochebruneanum ‘Lavender Mist’ lavender, yellow ⁄2 in. early Jul-Sep good purple/blue-green 75 in. 26 in. 1 HHHH rochebruneanum ‘Purple Mist’ lavender, yellow ⁄2 in. early Jul-Sep good purple/blue-green 72 in. 30 in.

Overall Ratings: HHHH good, HHH fair, HH poor. •Floral display consists of conspicuous stamens only due to absent or insignificant sepals. 1Flower coverage ratings: excellent 80-100%; good 60-80%; fair 40-60%; poor <40%. 2Emerging or early leaf color precedes the backslash, followed by the standard leaf color. CHICAGO BOTANIC GARDEN Plant Evaluation Notes 3 Richard Hawke Richard Richard Hawke Richard Photographed at Olbrich Botanical Gardens, Madison, WI by Richard Hawke Richard WI by Madison, at Olbrich Gardens, Botanical Photographed

Thalictrum lucidum Thalictrum flavum ssp. glaucum Thalictrum aquilegiifolium

Mist’, T. ‘Elin’ and T. aquilegiifolium back after flowering to rejuvenate plant sepals were inconspicuous and abscised ‘Purpureum’. health. A small amount of leaf miner early. The floral effect was more textural Thalictrum flavum ssp. glaucum (yel- damage was observed in 2002 and 2003, than colorful due to the small size of the low meadow rue) was a robust, rhizoma- but was superficial and did not have an flowers and the openness of the inflores- tous plant with stems spreading up to 6 effect on plant health. cences. The fine-textured foliage, resem- feet from the original plot by the fourth Thalictrum kiusianum (Kyushu mead- bling the fronds of maidenhair fern year of the trial. The rhizomatous stems ow rue) was the smallest species in the (Adiantum), emerged with a bronze cast did not grow into a thicket but instead trial, only 2 inches tall without flowers. before turning blue-green. Stems stayed developed satellite plantlets nearby the Flower production was especially strong upright during the bloom period, but typ- original plants. Emerging leaves and each year, smothering the green foliage in ically declined late in the summer. In young stems were purple, eventually fuzzy pink flowers at peak bloom. Kyushu some years, stems were cut back in August changing to dusty blue-green in June. meadow rue remained healthy through- and quickly regenerated into healthy The yellow flowers, comprised of stamens out the trial and performed better than foliar mounds. Lesser meadow rue had a only, were held in broad, 6-inch wide ter- the slightly taller Thalictrum ichangense in slow-growing, rhizomatous habit but minal inflorescences in June and July. the environment of the test garden. No plants remained discrete during the trial Some repeat bloom in late August was winter injury was observed, but like period. noted in the lower leaf axils. Plant health T. ichangense, it did not compete well The trial plants of Thalictrum pubes- commonly declined after flowering, so with weeds early in the season. cens (tall meadow rue) were grown from stems were regularly pruned to the ground Linear leaflets differentiated wild-collected seed received from Mt. at the end of August. Stem regeneration Thalictrum lucidum from other meadow Cuba Center, Greenville, Delaware. was robust, resulting in bushy mounds rues in the trial. The bi- to tri-ternately Consequently, variation in habit, stem several weeks after pruning. Leaf miners compound leaves emerged purple, even- height and flower production was noted caused slight cosmetic damage in 2001 tually changing to lustrous green. This among the seedlings. In general, T. pubes- and 2003 only. Thalictrum flavum ssp. species put on an outstanding show in cens exhibited heavy flower production glaucum ‘True Blue’ was comparable to bloom, with puffs of pale yellow flowers in and robust habits with stiff stems. The yellow meadow rue in floral display and pyramidal clusters up to 9 inches wide. creamy white flowers, comprised of sta- flower production, but its stems were typ- The fluffy effect was due to clusters of mens only, were produced on stem termi- ically uneven in height among the plants prominent stamens subtended by tiny, nals and in lower leaf axils. The upper and often lodged early in the season. insignificant sepals. Thalictrum lucidum portion of the stems typically defoliated The leaves of Thalictrum flavum had a robust habit with stems that after flowering, thus creating an open ‘Illuminator’ emerged yellow with a remained upright all summer. effect in late summer. Stems were cut back twice in the trial, followed by a bronze tint, eventually changing to blue- ‘Adiantifolium’ speedy regeneration of basal leaves. green as flower buds swelled in June. (lesser meadow rue) featured flowers with Stems remained upright throughout the pendulous yellow stamens held in loose Flowers of Thalictrum roche- bloom period, but were occasionally cut clusters above the foliage; the greenish bruneanum (lavender mist or lavender CHICAGO BOTANIC GARDEN Plant Evaluation Notes 4 Richard Hawke Richard Richard Hawke Richard

Thalictrum ‘Elin’ Thalictrum flavum ‘Illuminator’ mist meadow rue) feature prominent bloom was noted in the lower leaf axils lavender sepals surrounding a cluster of later in the summer too. However, the yellow stamens. The persistent and color- new leaves remained purple longer than ful sepals set this species apart from many on lavender mist, beginning to fade when of the other taxa in the trial. Leaves flower buds swelled in mid-June. The emerged purple, eventually fading to plant vigor of ‘Elin’ surpassed either of its blue-green by late May. Lavender mist parents, with stems ultimately reaching 8 typically has a sparse or see-through qual- feet tall. ‘Elin’ maintained a dense, bushy ity to its habit. This trait was accentuated habit throughout the summer, and did by the fact that the lush lower leaves pres- not drop leaves and thin out like T. roche- ent in the early season gradually turned bruneanum. Severe powdery mildew was yellow and dropped throughout the sum- observed in 2001 and 2003; slight leaf mer. Stems remained upright all summer miner damage was noted in most years with secondary bloom noted in the lower but did not affect the ornamental quality leaf axils into September. of the plant. There was no discernible difference The specific epithet and common in the floral traits and floral displays of name of Thalictrum aquilegiifolium Thalictrum rochebruneanum, ‘Lavender (columbine meadow rue) refer to the Mist’ and ‘Purple Mist’. In addition, the foliar resemblance to columbine emerged with purple leaves and (Aquilegia). Their pomponlike flowers are were comparable to the species in size. made up of pale lavender stamens held in Whereas the species was pest-free during broad inflorescences up to 6 inches wide. the trial, ‘Lavender Mist’ and ‘Purple The flower color of ‘Purpureum’ was vari- Mist’ had minor powdery mildew infec- able within the test group and only slight- tions in 1999, 2001 and 2003. Seedlings ly darker than the species. The plants of of Thalictrum rochebruneanum and/or its ‘Purpureum’ were generally more robust cultivars were commonly observed in the and floriferous than T. aquilegiifolium and test plots. T. aquilegiifolium var. album. Flowers of Thalictrum ‘Elin’ is a reputed hybrid var. album were actually very pale laven- between T. rochebruneanum and T. flavum der, not pure white. ssp. glaucum, although it resembles the The vigor of Thalictrum aquilegiifolium, former species more than the latter. including ‘Purpureum’ and var. album, Flower color and size was comparable to was weakened by the cultural T. rochebruneanum but ‘Elin’ bloomed conditions of the test site; inconsistent slightly earlier each year; secondary soil moisture and full-sun exposure CHICAGO BOTANIC GARDEN Plant Evaluation Notes 5 Carol Freeman Carol Jen Van Wagoner Van Jen

Thalictrum aquilegiifolium ‘Purpureum’ Thalictrum rochebruneanum resulted in rapid foliar decline after flow- for two more years, ultimately dying in ering. On the other hand, these meadow the winter of 2000-01. Unfortunately, rues were the earliest to bloom so their this taxon was not retested to determine premature decline may have been partial- if healthy plants would perform differently. ly due to natural senescence, which was Conversely, T. delavayi ‘Hewitt’s Double’ exacerbated by the conditions of the site. was replanted and evaluated three times In addition, powdery mildew was a minor between 1998 and 2001. In each to moderate problem following the bloom instance, all plants died during the subse- period in all years of the trial. quent winter after just one summer in Thalictrum actaeifolium (baneberry- the trial. leaf meadow rue) was one of three taxa Thalictrum ichangense (Korean mead- that received a poor final rating. In this ow rue) was the second shortest species in instance, the poor rating was due to low the trial, only 6 inches tall without flow- flower production, lack of plant vigor and ers. The few-flowered inflorescences were excessive winter injury. The fuzzy flowers sparsely produced each year, although were made up of bicolored stamens with repeat bloom was observed periodically lavender filaments and white anthers, but throughout summer and into October. were sparsely produced each year. Stems Pale lavender stamens provided the floral remained upright during the bloom peri- display because the sepals fell off soon od but became floppy soon afterward. after the flowers opened. The peltate Plants were weakened by crown damage leaves were held perpendicular to the in the winter of 1999-2000 and never stems, thus exposing silvery glaucous fully recovered their health in subsequent undersides. Stems were late to emerge in years. In addition, seven plants were spring, so early season weeds often crowd- killed in the winter of 2002-03, leaving ed out young shoots if the weeds were not only one plant alive in the final year of removed promptly. Korean meadow rue the trial. received a poor overall rating because of (Yunnan meadow low flower production and excessive win- rue) was the only taxon with a general ter injury. Many of the plants suffered lack of plant vigor attributed to poor serious crown damage in the winter of establishment after planting. Poor health 2000-01, with additional plants killed in and a weakened condition during the first the winters of 2001-02 and 2002-03. summer likely contributed to the death of Summary seven of the eight plants over the winter Although commonly recommended of 1998-99. The remaining plant survived for shadier sites, a majority of the meadow CHICAGO BOTANIC GARDEN Plant Evaluation Notes 6 rues in the study thrived in full sun and are recommended for gardens with similar cultural conditions. Eleven different Wild-collected Thalictrum Species meadow rues, from tiny Thalictrum kiuisianum to lofty ‘Elin’, received top reproductive characteristics were care- honors—a four-star good rating based on fully observed to ascertain weediness,

Jenny Lee Jenny which could potentially lead to inva- higher flower production, superior plant siveness. A number of the taxa were habits, winter hardiness and good plant readily adaptable to garden culture but health. Conversely, Thalictrum aquilegi- had limited ornamental appeal and/or ifolium is not recommended for full sun had vigorously spreading habits. In the unless consistent soil moisture is provid- end, none of the wild-collected species ed. Meadow rues are easy-care perennials in the trial are recommended for gar- for a variety of garden uses, showing den use due to weedy habits, lack of exceptional diversity in their flowers, ornamental traits or poor performance. foliage and habits. They offer gardeners In addition, commercial sources in the tempting design potential because of their United States were not found for many versatility. of these plants. Thalictrum simplex References Floral displays, specifically flower Armitage, A. M. 1997. Herbaceous The Chicago Botanic Garden color, were inferior when compared to Perennial Plants, Second Edition. evaluated eight Thalictrum species col- any of the cultivated taxa in the trial. Champaign, IL: Stipes Publishing. lected in the wild during three plant These species generally had nonde- script yellow or purplish flowers. Lord, T., principal editor. 2005. RHS exploration trips to Russia between Thalictrum amurense, T. appendicula- Plant Finder 2005-2006, Eighteenth 1993 and 1997. These species were tum, T. simplex and T. tuberiferum Edition. London, UK: Dorling Kindersley collected as seed in their native habi- tats in the Altai Mountains of Central exhibited exceptionally heavy flower Limited. Siberia, the Lake Baikal region of production each year. On the other Phillips, E. and C. C. Burrell. 2004. Siberia and the Far East of Russia. hand, the floral display of T. altaicum, Rodale’s Illustrated Encyclopedia of Thalictrum altaicum (syn. T. T. baicalense and T. foetidum was con- Perennials. Emmaus, PA: Rodale Press. schischkinii), T. minus and T. simplex sistently recorded as unremarkable or Rice, G., editor-in-chief. 2006. American were collected in the Altai Mountains nonornamental due to low production Horticultural Society Encyclopedia of in 1993 and evaluated from 1995 and/or inferior color. Perennials. New York, NY: DK through 1999; Thalictrum appendicula- Species with rhizomatous plant Publishing, Inc. tum (syn. T. minus ssp. minus), T. habits were variably described in the baicalense and T. foetidum were collect- trial as aggressively spreading, weedy or ed in the Lake Baikal region in 1994 potentially invasive, including and evaluated from 1995 through Thalictrum altaicum, T. amurense, T. 1999; and Thalictrum amurense (syn. T. appendiculatum and T. tuberiferum. In flavum ssp. flavum) and T. tuberiferum addition, T. amurense, T. appendicula- were collected in the Russian Far East tum and T. tuberiferum were observed in 1997 and evaluated from 1999 to reseed readily in the test site. through 2003. These species were Thalictrum foetidum was severely grown under the same cultural condi- injured during the winter of 1997-98 tions as the meadow rues in the second and all remaining plants died during trial; that is, full sun, well-drained soil, the following winter. Thalictrum minus pH of 7.4 and protection from deer was in poor health when planted in browsing. 1995 and struggled through two grow- The wild-collected species were ing seasons before dying during the evaluated for the same criteria as the winter of 1996-97. Thalictrum altaicum commercially available meadow rues, was healthy for two years but died out but their habits, growth rates and completely in the winter of 1996-97. None of the taxa was retested.

The Plant Evaluation Program is supported by the Woman’s Board of the Chicago Horticultural Society and the Searle Research Endowment.

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