Prairie dock (Silphium terebinthinaceum) is a perennial plant that will grow to 2.5 m tall. The leaves have a sandpaper texture and are 46 cm long. Blooms in summer with a tall flowering stalk filled with showy, yellow flowers. The nectar attracts all kinds of bees and the seeds provide food for goldfinches. Drought-resistant, it grows in full sun or partial shade.
I. Appearance and Characteristics
Silphium terebinthinaceum is a member of the Asteraceae, a family that includes sunflowers, and is commonly referred to as prairie dock or prairie rosinweed.
Silphium terebinthinaceum is native in the United States from Iowa, Missouri, and Arkansas to the west, Wisconsin to the north, Virginia to the east, and Mississippi, Alabama, and Georgia to the South. In Canada, it is native to Ontario, although it is critically imperiled. The habitats of S. terebinthinaceum include black soil prairies as well as gravel, shrub, and hill prairies. It also prefers to grow alongside roads and railroads.
Silphium terebinthinaceum is an herbaceous perennial growing 3 to 10 feet (1 to 3 m) tall. Prairie dock produces small yellow flowers about 2–2+1⁄2 inches (5–6 cm) in diameter in the summer. The leaves are rough-textured, spade-shaped, and oriented vertically and in a north–south direction, providing special adaptations for survival in the prairie climate. One study found that the majority of prairie dock’s leaves were oriented within 15° of North as well as 60° away from the horizontal.
The combination of north–south and vertical arrangement seems to provide a mechanism for maintaining lower leaf temperatures at midday, thus conserving water. Additionally, this unique trait grants the plant better access to sunlight for photosynthesis, and consequently provides a more efficient method of producing its carbon resource. This dicot also has a characteristically large taproot able to penetrate to depths of at least 14 feet (4 m) in search of the water table.
Silphium terebinthinaceum prefers full sun. S. terebinthinaceum is a drought-resistant plant that thrives in slightly dry to moist environments. While S. terebinthinaceum prefers deep loamy soils, it is tolerant of soils with gravel and rocks. The plant is slow at developing but is strong and difficult to kill when it is mature. Even though it is a robust plant, harsh conditions may still affect this plant. When there is a drought, a windstorm, or damage to the leaves of the S. terebinthinaceum, patches of brown can develop. Recovery after wildfires occurs quickly, as it has a very deep taproot.
Silphium terebinthinaceum can survive destructive events such as grazing and soil degradation because of its ability to produce new above-ground shoots. This plant is also well adapted to obtain and hold onto water due to its characteristically large taproot and large, particularly oriented leaves. Native bees nest beneath or within these plants or use elements of the plants for their nests. Consequently, they are thought to be an important species for attracting bees for pollination in the area. Prairie dock is one of the few species that successfully persists on land that has been converted from prairie to railway.
II. How to Grow and Care
Sunlight and Soil
Prairie dock performs best in full sun in average, medium moisture, well-drained soils. It tolerates poor soils. The flower stalks can be floppy in shady conditions
Watering
Native to the prairies of North America, prairie dock is well-adapted to environments with intermittent rainfall and has developed a tolerance for periods of drought. This species thrives in conditions that mimic its natural habitat, where water availability can be sporadic. As such, it requires watering once every 1-2 weeks, allowing the soil to dry out slightly between waterings. Given its resilience, prairie dock is an ideal candidate for outdoor cultivation where it can benefit from natural precipitation patterns. It particularly excels in regions where the growing season aligns with rain cycles, reducing the need for supplemental irrigation.
Fertilizing
To maintain vigor and promote robust growth, prairie dock benefits from balanced nutrition fertilizers. A higher phosphorus mix during the early growth stages enhances root development and flowering. Fertilize prairie dock sparingly in spring and fall, avoiding over-fertilization, which can be harmful. Use granular or liquid fertilizer according to label instructions, but not exceeding the recommended amount. Special care: Do not let fertilizer directly contact stems or leaves. Seasonal adjustments may be required, with minimal to no fertilization necessary during dormant winter months.
Pruning
Regular deadheading is not necessary, but removing old flower stalks can promote aesthetic appeal.
Propagation
Prairie dock is a robust perennial native to North American prairies, known for its large basal leaves and towering flower stalks. For successful propagation of prairie dock, starting from seeds is the most effective method. Ensure a well-drained soil mix and use a cold stratification process to break seed dormancy, as this mimics the natural chilling period seeds experience in the wild. Once stratified, sow the seeds in a sunny location within the prepared soil. Regular watering and minimal disturbance will encourage germination and establishment. As prairie dock matures, it will form deep roots, making it resilient and low maintenance in appropriate climatic conditions.
Transplanting
Optimal relocation of prairie dock is best approached as the rejuvenating season unfurls, with warming soils providing prime conditions. Select sunny spots with deep, rich earth. Delicate care in positioning roots ensures prairie dock’s robust revival.
III. Uses and Benefits
- Ornamental uses
Prairie dock is great for prairies or meadows, cottage gardens, wildflower gardens, and beds and borders.
- Medicinal uses
Like Silphium perfoliatum (cup plant), S. terebinthinaceum is used as a tea to relieve lung bleeding, to minimize menstruation bleeding, and as an emetic by Native Americans. Other root tea uses include a treatment for liver issues, fever, and enlarged spleen. The smoke from this plant is used as a treatment for nerve pain, along with relieving congestion and rheumatism. However, this plant is considered potentially toxic.
