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
Before flowering, Rosin Weed can be mistaken for Milkweed. While flowering, it resembles a Sunflower although it blooms earlier than the native Sunflowers. It may be the best Silphium choice for a garden setting due to its shorter stature, ability to mature faster, and tough stem that keeps it upright with little to no surrounding plant support. It is aggressive though, so choose a spot where it can’t overwhelm smaller plants.
Though not nearly as tall and stately as its cousin, Compass Plant, Rosin Weed is nonetheless a wonderful choice for a native garden, especially if you are concerned with drought. When it comes to tolerating dry soils, few plants are as hardy as Rosin Weed. With its deep taproot, this species will keep its composure while other plants whither. Small rhizomes will extend from this taproot allowing it to form small colonies, albeit slowly. Unlike many composite flowers, which have fertile disk flowers and sterile ray flowers, Rosin Weed exhibits the exact opposite. It is the showy ray flowers that are fertile.
Rosin Weed attracts a variety of pollinators but it is especially relished by some of our smaller solitary bees. The plant gets its common name from the sticky rosin it produces, which was used as a chewing gum by the Native Americans. Rosin weed is quick to mature once germinated, reaching flowering size surprisingly fast.
Price range: $6.00 through $12.00
