Rosin Weed - Silphium integrifolium

Culture: Easily grown in average, medium moisture, well-drained soils in full sun. Tolerates some light shade. Also tolerates some drought once established. Will grow in a variety of soils including sandy, loamy or clay ones. Plants may be slow to establish in the garden, particularly when grown from seed. Plants often self-seed in optimum growing conditions. Plants develop taproots. Once established, division is not recommended.

Noteworthy Characteristics: Silphium integrifolium, commonly called rosinweed or wholeleaf rosinweed, is a coarse, sunflower-like perennial that derives its common name from the resinous gummy sap exuded by broken/cut plant stems. It grows shorter (often to 2-3’ tall) than most of the other native silphiums, though it may grow as tall as 6’. It is native from Michigan to Wyoming south to Alabama and New Mexico. In , it typically occurs in rocky or dry open woods, prairies and glades throughout the state except for several far southeastern counties. It grows on erect, hairy stems sparsely clad with pairs of rough, stalkless, bristly, hairless to woolly, toothed to toothless, medium green leaves (to 6” long). Leaves are quite variable in shape, ranging from lanceolate to ovate to elliptic. Flowers (to 2-3” diameter) resembling small sunflowers appear in corymb-like inflorescences in mid-summer. Each flower features yellow rays and a yellow center disk. Flowers are subtended by bracts with reflexed tips.The genus name Silphium comes from the Greek name silphion, used to refer to a North African resin bearing plant.Specific epithet means with entire or uncut leaves.

Problems: No serious insect or disease problems. Downy mildew, leaf spots and rust may occur.

Garden Uses: Best planted in groups where it can naturalize. Some gardeners find it to be too weedy for borders, but others find it to be an effective backdrop for other perennials. Adapts well to prairies, wildflower/native plant gardens, naturalized areas, meadows or moist, open woodland areas.

All plant information courtesy of the Missouri Botanical Garden