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Cabbage-leaf Coneflower—A Composite with Presence
Plants & Gardens News Volume 12, Number 4 | Winter 1997
by Bob Hyland
Commonly called cabbage leaf coneflower, Rudbeckia maxima is an eye-catching perennial native to warm, moist pine woods and plains from Arkansas to Louisiana and into Texas. However, its range of acceptable climates extends farther north. R. maxima is an herbaceous perennial in USDA hardiness zones 6 to 8; plants go dormant in late fall and the foliage disappears until spring. But being a native of warmer southern regions, this rudbeckia thrives in hot, humid summers, such as those in Brooklyn and elsewhere in the East and Midwest.
Rudbeckia maxima forms attractive clumps or heads of foliage low to the ground; individual leaves are "paddle-shaped," 18 inches long and 3 to 4 inches wide. Their bluish-green surfaces are glaucous (covered with a waxy, whitish material that rubs off easily) producing an interesting sheen. The common name of cabbage leaf coneflower, although undoubtedly derived from the over-sized cabbage-looking leaves, does a disservice to this striking plant. For, out of the clumps of bluish-green leaves, tall architectural flower stems shoot up to the sky like rockets in mid to late summer and explode into rays of golden yellow.
In the last decade this stunning North American perennial has begun to capture the attention of American gardeners after being "rediscovered" in European gardens. As early as 1895, the virtues of Rudbeckia maxima were noted in The Garden published by the Royal Horticultural Society in England. In volume 41, page 418 of The Garden, author C. Wolley-Dod provides a portrait of eight yellow North American coneflowers including R. maxima. Described as "a fine, handsome plant . . . having flowers densely set with broad golden rays" the author goes on to say "I raised many plants of it ten years ago from American seed, and in 1887 and 1893 it was grand, but cold, wet summers, more than the frosts of winter, have greatly reduced the dimensions of the plants, which want renewing from imported seeds."
The real show comes in summertime when this perennial blooms from around July through September. Six- to seven-foot stems support bold drooping flowers that resemble soggy sombreros. The composite flower is actually composed of a prominent two-inch-long cone of tiny, black, tubular disk flowers surrounded by effervescent golden yellow ray flowers. The cone of dark disk flowers in the center of Rudbeckia maxima resembles a black eye—the common black-eyed Susan (Rudbeckia hirta) is, in fact, a member of the same plant genus.
Rudbeckia maxima can't be beat for vertical drama in both natural and formal gardens. It is excellent for meadows where it will boldly punctuate more delicate grasses and wildflowers. In mixed borders, it combines dramatically with shrubs, ground covers and other perennials.
Rudbeckia maxima is one of approximately 25 North American species of perennial, annual and biennial flowers commonly called coneflowers. Related species include the ever-popular Rudbeckia fulgida sullivantii 'Goldsturm', a hard-working, pest-free, lower-growing (three-foot-tall) coneflower that blooms from July through August. It is often planted in combination with ornamental grasses like Pennisetum alopecuroides (fountain grass) and Panicum virgatum. Another popular relative is Rudbeckia nitida 'Herbstsonne' ('Autumn Sun') that grows to 7 feet tall with bright yellow flowers around a raised central cone. Also a late bloomer, 'Autumn Sun' flowers from late August through September.
Easy to Grow
Rudbeckia maxima is generally pest- and disease-free, and easy to grow. Plant Rudbeckia maxima in full sun for best growth and effect, although plants will tolerate light shade. It does best in rich, moist soils, but will also grow in drier sites. Summer heat and humidity encourages good growth.
Staking is generally not required. The tall flower stems are sturdy and seem resilient even after rains or overhead irrigation have weighed them down. Companion shrubs and other perennials also lend support in mixed border compositions.
The quickest and easiest way to propagate Rudbeckia maxima is from divisions. Dig up and divide established clumps in September and plant divisions where desired in the garden. Remember to mulch divided plants to prevent winter frost heaving in colder climate zones.
Rudbeckia maxima can also be propagated from seed collected in the fall (September and October); seed is sometimes hard to find and difficult to germinate. If you want to try, first stratify or cool the seed in a refrigerator at approximately 40oF (4oC) for three months. Then sow the seed in flats or small pots filled with a lightweight soil mix. Young seedlings can be thinned and transplanted into individual containers during March and April and will be ready for transplanting into the garden in May and June.
Where to See It
In the perennial borders at the Brooklyn Botanic Garden, designer Conni Cross has intermingled Rudbeckia maxima with dwarf Hinoki false-cypress (Chamaecyparis obtusa 'Nana Gracilis'), oakleaf hydrangea (Hydrangea quercifolia), hybrid heath (Erica carnea 'Springwood White'), dwarf slender deutzia (Deutzia gracilis 'Nikko'), candytuft (Iberis sempervirens 'Little Gem') and white old-fashioned bleeding heart (Dicentra spectabilis 'Alba'). And before the new foliage of R. maxima appears, spring-blooming narcissus (Narcissus 'Thalia') adds early color and interest.
The blue-green foliage of this coneflower adds to the border's colorful hues, and the flowers, which reach their peak burst of bloom in August and September here, rise tall enough to be in clear view even when planted at the back of this mixed border.
Sources:
115 Lance Rd., P.O. Box 36
Fletcher, NC 28732-0368
704-891-7790
Bob Hyland is Vice President of Horticulture at Brooklyn Botanic Garden.