A Comparative Study of Ground Cover Lamium Mark R

Home , Lamium, Lamium album, Lamium maculatum, Lamium orvala

ISSUE 23, 2004 Plant Evaluation Notes A Comparative Study of Ground Cover Lamium Mark R. Rudy, Plant Evaluator

hady gardens offer a number of areas ranging from poor rocky slopes to forest spotted dead nettles are eye-catching plants challenges for gardeners. A variety of edges, dead nettles display a breadth of throughout the year. Slight levels as well as moisture cultural adaptability, something that has Exhibiting a more upright habit than gradients from soggy to dry can make it made them attractive to gardeners. In Lamium maculatum, white dead nettle difficult for gardeners to place the right plant addition, the genus Lamium provides a (L. album) is generally considered a weed in in the right location. The edge of the shade variety of plant habits from low-growing and Europe and grows in a number of sites garden often represents a sharp line of spreading to upright and rounded. including hedgerows, waste dumps and cultural change, where sun-loving plants Of the cultivated species, spotted dead alongside streams. Like spotted dead nettle, flop and shade-lovers scorch. However, nettles (Lamium maculatum) constitute the it spreads vigorously and is used as an there’s at least one group of plants able to majority of commercially available varieties. effective ground cover. Although it may stand up to the rigors of the unpredictable At the time of this publication, there were have an unfavorable reputation in some shaded garden. Dead nettles (Lamium) are 30 cultivars of L. maculatum listed in the parts of the world, it is actually considered by an ideal choice for the gardener who wants a RHS Plant Finder, compared to 11 cultivars some to be less aggressive than L. tough plant as well as a variety of foliage for all the other species combined. maculatum. White dead nettle combines colors and textures. Commonly used as a ground cover in the well with a variety of grasses, forget-me-nots, The genus Lamium contains shade garden, spotted dead nettle is short- primroses and other wildflowers. approximately 50 species from Europe and branched and stoloniferous and likely the Asia. Out of these, only a few have been most recognizable of all the dead nettles. DEAD NETTLES (LAMIUM) deemed ornamental. The species most Whether donning leaves with a silver stripe commonly under cultivation include or entirely silver, its appearance is unlike ARE AN IDEAL CHOICE FOR L. album, L. galeobdolon (syn. Lamiastrum other perennial ground covers and contrasts galeobdolon), L. maculatum and L. orvala. well with dark-leaved varieties of perennials THE GARDENER WHO WANTS This group is commonly referred to as dead such as coral bells (Heuchera ‘Velvet Night’) nettles due to their resemblance to stinging and black snakeroot (Cimicifuga ramosa A TOUGH PLANT AS WELL AS nettle (Urtica dioica); however, Lamium ‘Hillside Black Beauty’). Tolerance of a A VARIETY OF FOLIAGE species lack stinging hairs on their stems variety of light regimes makes it the ideal and leaves. plant to use as a transition between sunny COLORS AND TEXTURES. Lamium is well suited to a variety of and shady sites. With a long bloom period growing conditions. Naturally occurring in and colorful foliage, the many varieties of Giant dead nettle (Lamium orvala) possesses larger leaves as well as a greater stature than ground cover dead nettles. Jenny Lee Jenny Stems emerge from a central crown, are generally unbranched and combine to form a nearly spherical habit. Unlike its relatives, giant dead nettle does not spread readily, and any spread it does achieve is due to reseeding rather than vegetative growth. Leaves are up to 6 inches long, sharply toothed and typically solid green, although leaves with a silver stripe down the midrib have been documented in the wild. The species grows best in part shade and is tolerant of a variety of moisture regimes. It can be used in the garden in combination with spring bulbs, ferns and other woodland perennials. Regardless of differences in foliage and Lamium maculatum ‘ Red Nancy’ habit type, all dead nettles share the same 2 Plant Evaluation Notes CHICAGO BOTANIC GARDEN flower structure consistent with other birch, ginkgo and pine, and in most cases, and colors, another desirable attribute of members of the mint family (Lamiaceae). trial plants were planted in raised beds to many dead nettles is their exceptionally long The bilabiate, or two-lipped, flower consists maximize drainage. Protection was provided bloom period. In midwestern climates, it is of a distinct, large, hooded upper lip and a throughout the garden by wood fencing. The not unusual for varieties of Lamium smaller, bisected lower lip. Closer to the leaf clay-loam soil, amended with composted maculatum and L. album to bloom from axil, where the flowers first emerge, the lips leaves, had a pH of 7.4 throughout the spring until frost. Obviously, these plants are fuse together into a single tube or throat. In evaluation term. not at peak bloom for the entire period, and fact, the name Lamium is adapted from the Maintenance practices were kept to a may in fact persist at 5% to 10% coverage for Greek lamios, which means throat. minimum to simulate home garden culture. the final two months of bloom. Lamium Dead nettles are stalwarts of the shade A combination of overhead sprinklers and orvala and its cultivars tend to bloom for a garden, although their adaptability to a hand watering provided moisture as needed, more modest six weeks from spring to early variety of light and moisture regimes makes and no fertilizer was applied. Trial beds were summer, but blooms densely populate the them worthy candidates for sites that receive weeded, and mulch consisting of shredded leaf axils for the majority of the time. Any more light throughout the day. In addition, leaves and wood chips was placed around the taxa that did not meet their potential bloom unique foliage colors and textures allow the plants for weed suppression and water length received a lower rating. gardener to combine Lamium species and conservation. Plant health and habit quality cultivars with each other as well as with throughout the trial period are always Observations other annuals and perennials. significant factors in the determination of From 1998 to 2003, 21 taxa of Lamium plant performance. While health is generally The Evaluation Project were evaluated, including 17 varieties of judged the same for all plants, habit quality In 1998, the Chicago Botanic Garden L. maculatum, one variety of L. album and rating depends on the desired shape or (USDA Hardiness Zone 5b, AHS Plant three varieties of L. orvala. Of these, 15 taxa garden use of the plant group being trialed. Heat-Zone 5) gathered commercially survived for more than two seasons and In the case of Lamium maculatum and available Lamium taxa, concentrating on received final ratings (Table 1). Based on the L. album, plants were expected to have cultivars of L. maculatum, for a multi-year performance of the Lamium group, the continuous mats of foliage without holes or evaluation study. Observations of the initial following criteria determined final ratings: unsightly upright stems. Lamium orvala evaluation group began in 1998 with 1) peak flower coverage; 2) length of bloom varieties were expected to maintain dense, subsequent additions as the trial expanded to period; 3) plant health; 4) plant habit rounded habits. include L. album and L. orvala, and newly quality; and 5) cultural adaptability. The Finally, a factor that significantly available L. maculatum cultivars. The amount of flower production was a affected the performance ratings of Lamium project concluded at the end of the 2003 significant factor in the comparison between varieties was cultural adaptability. Upon growing season. The goal was to recommend the excellent and mediocre performers. initial inspection, plant losses during the superior taxa based on general health and Regardless of the species examined, flowers winter pointed to a lack of cold hardiness. habit, bloom coverage, length of bloom, pest were consistently borne on the upper half to However, none of the varieties studied were and disease resistance, and cultural upper third of the stems. However, flowers known to be susceptible to severe winter adaptability. were seldom displayed on all stems. For this injury in our climate. A closer look at our All dead nettle taxa were grown in the reason, peak coverage of 60% or greater was site revealed that the soil had a higher Pullman Shade Evaluation Garden. Shade considered excellent. moisture content than was likely ideal for was provided by mature trees including oak, In addition to the variety of leaf forms

Table 1: Plant Characteristics and Performance Summary Ratings Overall Lamium Leaf Character Flower Color Peak Flower Bloom Period Height Width Rating overage1 ##### album ‘Friday’ variegated green white 30-50% late Apr-mid Sep 22 in. 36 in. ##### maculatum ‘Album’ green, silver stripe white 30-50% late Apr-late Sep 8 in. 20 in. #### maculatum ‘Beacon Silver’ silver, green margin purple-pink 30-50% late Apr-late Sep 9 in. 19 in. #### maculatum ‘Beedham’s White’ yellow, white stripe white 10-25% late May-mid Oct 9 in. 35 in. ### maculatum ‘Brocade’ silver, green margin rose-pink <10% late Apr-late Aug 5 in. 19 in. #### maculatum ‘Chequers’ green, silver stripe violet 30-50% late Apr-mid Oct 12 in. 26 in. #### maculatum ‘Elisabeth de Haas’ green/yellow streaks, white stripe pink 30-50% early May-late Sep 13 in. 27 in. #### maculatum ‘Pink Nancy’ silver, green margin pale pink 30-50% early May-mid Aug 6 in. 10 in. #### maculatum ‘Pink Pearls’ green, silver stripe pink 30-50% late Apr-late Sep 9 in. 19 in. #### maculatum ‘Pink Pewter’ silver, green margin pink 30-50% late Apr-mid Sep 6 in. 18 in. ##### maculatum ‘Red Nancy’ silver, green margin purple-pink 60+% mid May-mid Sep 6 in. 35 in. ##### maculatum ‘Shell Pink’ green, silver stripe pink 60+% late May-early Oct 12 in. 24 in. #### maculatum ‘White Nancy’ silver, green margin white 10-25% mid May-mid Sep 6 in. 21 in. #### orvala ‘Album’ green creamy white 30-50% early Apr-late Jun 26 in. 32 in. #### orvala ‘Silva’ green dusty pink 30-50% late Apr-late Jun 36 in. 53 in. Overall Ratings: ★★★★★ excellent, ★★★★ good, ★★★ fair, ★★ poor, ★ very poor; half-star ratings included in table. 1Ratings of peak flower coverage ranges: 60+% = excellent; 30-50% = good; 10-25% = fair; <10% = poor 3 Plant Evaluation Notes CHICAGO BOTANIC GARDEN Jenny Lee Jenny Jenny Lee Jenny Mark Rudy

Lamium maculatum ‘Shell Pink’ Lamium orvala ‘Silva’ Lamium maculatum ‘Beedham’s White’

Table 2: Plants surviving less than two years of trial flowered variety was rated slightly ‘Beedham’s White’ did not demonstrate the Lamium Reason lower than ‘Shell Pink’ due to a same tolerance as other Lamium varieties, maculatum ‘Angel Wings’ poor cultural adaptability maculatum ‘Anne Greenaway’ poor cultural adaptability shorter bloom time and lower with plants dying out during the first winter. maculatum ‘Ickwell Beauty’ poor cultural adaptability maximum flower coverage, but it This lack of cultural adaptability, coupled maculatum ‘Orchid Frost’ poor cultural adaptability exhibited superior traits to other with low flower coverage, is what kept maculatum ‘White Anniversary’ poor cultural adaptability orvala rabbit damage plants in the trial. ‘Beedham’s White’ from earning the highest Lamium maculatum ‘Red Nancy’ rating. this genus. Nevertheless, several varieties performed best of the taxa that possessed Aside from Lamium maculatum, several displayed outstanding adaptability to these predominantly silver foliage. Vigorous other dead nettles stood out as worthy plants conditions, while others did not. Since this growth and excellent flower coverage for Midwest gardens. Lamium album ‘Friday’ soil situation is common throughout garden separated this variety from other similarly features a coarser, taller habit than sites in the Midwest, adaptability to moist colored cultivars. Purple-pink flowers were L. maculatum and can appear weedy from a soils was deemed appropriate to use in the held clearly above the silver foliage with distance. Upon closer inspection, it has ranking of plants relative to one another. A dark green margins, but red-tinged stems interesting lance-shaped leaves with a list of dead nettles that died as a result of distinguished it from other pink-flowered variegation of three different shades of poor cultural adaptability is included in varieties. This trait was not as apparent as green. The white flowers offer contrast but Table 2. some references indicated, because stem are generally obscured by the foliage. ‘Friday’ Based on the evaluation criteria, nine pigmentation varied throughout the growing did spread, but it is likely not as aggressive as Lamium maculatum varieties received good season. ‘Red Nancy’ also made an effective the species, although this was the only L. to excellent ratings of four stars or greater. ground cover, as evidenced by its rapid album variety in the trial. The upright These included ‘Album’, ‘Beacon Silver’, spread during the trial period. Plants quickly flowering stems did show a propensity to flop ‘Beedham’s White’, ‘Chequers’, ‘Elisabeth de grew together within two years of planting to in mid- to late summer, creating a somewhat Haas’, ‘Pink Pearls’, ‘Pink Pewter’, ‘Red create a solid mass generally free of open unsightly, tangled appearance at times. Nancy’ and ‘Shell Pink’. spaces. The two cultivars of large-leaved Of the spotted dead nettles under trial, A departure from the green or silver Lamium orvala in this trial were both good four varieties had green leaves with a silver leaves of other dead nettles, Lamium performers overall. ‘Silva’, with dusty pink stripe in the midrib. Lamium maculatum maculatum ‘Beedham’s White’ has bright flowers, was generally a larger plant than ‘Shell Pink’ proved to be the best performer yellow foliage with a white stripe and white ‘Album’. In the spring and early summer, of this group. In fact, it was the only plant in flowers. More than any other Lamium these plants had tight, nearly spherical the dead nettle trial to receive a five-star variety, ‘Beedham’s White’ can brighten the habits that rival many small or medium-sized excellent rating. In addition to its abundant darker corners of the shade garden. A shrubs. Plants became somewhat leggy after coverage of clear pink blossoms and preliminary trial of ‘Beedham’s White’ was flowering and had a tendency to flop open as extended bloom period, ‘Shell Pink’ had conducted from 1993 to 1999. As the lone summer wore on. As an alternative, giant excellent health and the best habit of all the variety that preceded the main evaluation dead nettles can be grown for early season L. maculatum varieties. ‘Shell Pink’ group, it had the benefit of being grown in a interest and then cut back when habits maintained a full, mounded habit and was a number of different sites within the trial become floppy or open, much like Dicentra fast spreader, making it an effective ground gardens. In a site with even-to-dry moisture spectabilis (common bleeding heart) or cover. Lamium maculatum ‘Album’ was levels, this variety thrived, forming a dense Euphorbia palustris (marsh spurge). another excellent performer out of the group mat of bright yellow that eventually faded to Slugs and chewing insects were with silver-striped leaves. This white- chartreuse. However, in moister sites common pests that dead nettles faced during 4 Plant Evaluation Notes CHICAGO BOTANIC GARDEN the trial period. Slug damage left holes in the interior of leaves and chewing insect damage Jenny Lee Jenny created notches along the margins. A Mark Rudy significant occurrence of slug damage was noted in early June of 2001 following several days of high humidity and fog coupled with temperatures 15°F below average. Cultivars of Lamium maculatum that exhibited some degree of slug damage included ‘Album’, ‘Beacon Silver’, ‘Brocade’, ‘Pink Nancy’, ‘Pink Pewter’, ‘Red Nancy’, ‘Shell Pink’ and ‘White Nancy’. Chewing insect damage occurred over a wider span of time than slug damage, Lamium album ‘Friday’ Lamium maculatum ‘White Nancy’ ranging anywhere from late June to late August in multiple years. Varieties Conclusion damage from chewing insects and slugs had exhibiting chewing insect damage included Among the challenges that face the little more than a temporary impact on plant Lamium album ‘Friday’, L. maculatum shade gardener, unpredictable light and appearance. ‘Beedham’s White’, L. maculatum ‘Beacon uneven moisture regimes can make the Dead nettles offer a number of Silver’, L. maculatum ‘Brocade’, L. placement of plants in the shady garden an advantages in the shade garden and beyond. maculatum ‘Red Nancy’, L. maculatum all-or-nothing experiment. In these The ability to adapt to a variety of ‘Shell Pink’, L. maculatum ‘White Nancy’ circumstances, a variety of dead nettles come conditions makes them ideal for spaces and L. orvala ‘Silva’. Generally, damage to the rescue. From green, silver, yellow and where other plants have languished and from slugs and chewing insects was not variegated leaves to ground covers and died. Numerous varieties of Lamium significant enough to affect the overall upright habits, dead nettles offer ornamental maculatum maintain a reputation as appearance of any of the plants being versatility as well as a tolerance to a wide effective ground covers in shady situations. studied. Lamium orvala was so badly range of conditions. A breadth of cultural In addition, varieties of white dead nettle damaged by rabbits in its first year that it did adaptability gives dead nettles the upper and giant dead nettle expand the palette of not survive (see Table 2) and was not hand whether growing in deep shade or plant sizes and foliar textures. Whether retested. along the sunny edges of the garden. Dead several varieties are grown together as a Though they are tough garden plants, nettles combine well with ferns, spring bulbs tapestry or combined with annuals, dead nettles are not entirely maintenance and a variety of wildflowers, among other perennials and shrubs, dead nettles stand up free. A high level of promiscuity leads to plants. to the challenges of the unpredictable shade large numbers of seedlings annually, and Indicating their excellent overall garden. without some attention to weeding and performance as a plant group, 12 Lamium maintenance, new seedlings may overtake taxa received ratings of four stars or greater, References Armitage, A.M. 1997. Herbaceous Perennial Plants, the original plants. Lamium cultivars do not including L. album ‘Friday’, L. maculatum Second Edition. Champaign, Ill.: Stipes Publishing. remain true from seed; therefore, seedlings ‘Album’, L. maculatum ‘Beacon Silver’, Jelitto, L. and W. Schacht. 1990. Hardy Herbaceous Perennials, Volume II, L-Z. Portland, Ore.: Timber should be removed to maintain the integrity L. maculatum ‘Beedham’s White’, Press. of the cultivars that were originally planted. L. maculatum ‘Chequers’, L. maculatum Leslie, A. 2001. “Grasping the Nettle”. The Garden Seedlings of L. maculatum are easy to spot ‘Elisabeth de Haas’, L. maculatum ‘Pink 126(7): 542-545. among the silver- and yellow-leaved Pearls’, L. maculatum ‘Pink Pewter’, Lord, T., principal editor. 2003. RHS Plant Finder 2003-2004, Sixteenth Edition. London, U.K.: Dorling varieties, since the true species has green L. maculatum ‘Red Nancy’, L. maculatum Kindersley Limited. leaves with a silver stripe. Weeding out ‘Shell Pink’, L. orvala ‘Album’ and L. orvala MacKenzie, D.S. 1997. Perennial Ground Covers. seedlings among silver-striped varieties can ‘Silva’. These varieties possessed good flower Portland, Ore.: Timber Press. coverage and long bloom periods as well as Phillips, R. and M. Rix. 1991. The Random House prove more challenging, as it requires proper Book of Early Perennials, Volume I. New York: Random identification using flower color or subtle good cultural adaptability. Poor cultural House Inc. variations in leaf traits to distinguish adaptability to wet soils was the greatest differences. factor in the failure of a few taxa, while

The Plant Evaluation Program is supported by the Woman’s Board of the Chicago Horticultural Society and the Searle Research Endowment. Thanks to Richard G. Hawke and Jenny S. Lee for their assistance in collecting data.

Plant Evaluation Notes© are periodic publications of the Chicago Botanic Garden. For more information or copies of back issues, contact the Plant Evaluation Program, Chicago Botanic Garden, 1000 Lake Cook Road, Glencoe, Illinois 60022. The Chicago Botanic Garden is owned by the Forest Preserve District of Cook County.