Sunday, July 12, 2009

Kidneyleaf Rosinweed - Silphium compositum

Though I hate "Kidneyleaf rosinweed" as this species' common name, it is the one most widely used for this wonderful wildflower. In actuality, the leaves are not kidney-shaped at all, but deeply lobed. The leaves are one of the most attractive features of the plant and they add immense character to a mixed wildflower planting during the months it is not blooming.

Kidneyleaf rosinweed is native to sandy uplands throughout much of Florida's panhandle and south to Pasco County on the west coast. It prefers full sun, but also occurs in open woodlands and woodland edges where it receives less. In these habitats, it produces a deep tap root. It will not succeed in areas where this tap root cannot extend (e.g. areas with a shallow confining layer of clay or limestone in the soil) or in areas that stay too wet. Given the proper soils and drainage, however, this wildflower is wonderful.

Well-established plants (2 years old and older) produce a large rosette of basal leaves in the spring. Each leaf may be 12-18 inches long and well more than a dozen may be produced. These are a rich green in color and deeply lobed and/or toothed.

The flower stalk is evident by late spring and quickly grows skyward. Flowering begins in July and is usually finished by August in Florida. Flower stalks can reach 6-8 feet in height and often are composed of over a dozen flower heards.

While its close cousin, starry rosinweed (S. asteriscus), has become widely available to Florida gardeners, kidneyleaf rosinweed has not for some reason. Though its flowers are a bit smaller, it makes up for that in its amazing foliage and exceptional drought tolerance.

Use this plant in a mixed planting of wildflowers with similar soil and sun requirements. Good companion plants are various blazing stars (Liatris spp.), resindot sunflower (Helianthus resinosus), summer farewell (Dalea pinnata), grassleaf goldenaster (Pityopsis graminifolia), and various true asters (Symphyotrichum spp.). Because it gets tall, use it in the back of the planting; and because the basal leaves get large, plant individuals at least 12 inches apart. I prefer it planted in small isolated clumps instead of as individual plants.

Kidneyleaf rosinweed is a wonderful nectar source for butterflies and a seed source for seed-eating songbirds. Hawthorn Hill is proud to be producing this wildflower for the general public. Our plants are grown from seed originally collected in Citrus and Hernano Counties - near the southern end of its Florida range. We have been growing it successfully now in our Pinellas County landscape for 2 years and believe it is adaptable south of its natural range if planted in well-drained soil.


  1. Can you tell me about the salt tolerance of this plant and it's cousin starry rosinweed?

  2. I do not believe either of the Silphiums have much tolerance for salt. I have never seen them, or their out-of-state relatives near a coast before. If I lived on a coastal property, I might try them on the side of the house away from the water - where they would be ~protected from salt spray. But, if the area were to be inundated by such thing as a tropical storm, I expect they would perish.


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