Overview
Silphium perfoliatum L. var. perfoliatum, commonly known as cup plant, is a herbaceous biennial or perennial plant of the daisy family, Asteraceae. The plant is native to North America and can be found in moist areas such as wet meadows, riverbanks, and marshes.
Description
The cup plant can grow up to 2.5 meters in height, with a woody stem and large leaves that are positioned opposite each other on the stem and are fused together at their bases to form a cup. The flowers are bright yellow and bloom in mid to late summer, attracting a wide range of pollinators.
Uses
The tall, attractive cup plant is often used as a garden ornamental due to its large size and showy flowers. It has also been used for medicinal purposes by various Native American tribes. The leaves were sometimes used to make poultices to treat skin irritations, while the seeds were ground into a paste to treat sore throats and other internal ailments. The nectar and pollen of the plant are also a valuable food source for many insect species including bees, butterflies and moths.
Cultivation
Cup plant is a low maintenance plant that is easy to grow from seed. It prefers moist, well-drained soils and full sun to partial shade. The plant can self-seed freely and can become invasive in some areas. To control its spread, it is best to deadhead the spent flowers and remove any unwanted seedlings promptly.
Light requirements
Silphium perfoliatum L. var. perfoliatum thrives in full sun to partial shade. Full sunlight exposure results in greater growth and flowering. It is capable of tolerating partially shaded areas; however, the inflorescence size might decrease in such situations.
Temperature requirements
The plant grows best in a climate with a long growing season of cool temperatures. It prefers an average temperature range of 70-85°F during the growing season, and it has been found to be frost-resistant as well. During the winter, the plant becomes dormant or dies back to the ground and resprouts in the spring from the roots.
Soil requirements
Silphium perfoliatum L. var. perfoliatum prefers fertile, moist, well-drained soils but can tolerate a wide range of soil types. It is adapted to grow in loam soils, but it can grow in sandy or clay soils as well. This plant is especially adapted to grow in soils that are rich in organic matter, as they provide the necessary nutrients to produce robust growth and flowering.
Cultivation Methods
Silphium perfoliatum L. var. perfoliatum, commonly known as cup plant or compass plant, is a hardy perennial plant that thrives in well-drained soils with full sun to partial shade. Before planting, prepare the soil by removing any weeds or debris and incorporating organic matter such as compost or well-aged manure.
The best time to plant cup plant is in the spring, after the last frost date. Space the plants about 3-4 feet apart to allow for ample growth. Water the newly planted seedlings regularly for the first few weeks until they establish a strong root system.
Watering Needs
Cup plant prefers moist soil and requires regular watering, especially during dry periods. Provide 1 inch of water weekly, either through rainfall or irrigation. It is important not to overwater, as this can lead to root rot and other fungal diseases.
To avoid wetting the leaves and increase water absorption, water at the base of the plant using a drip irrigation system or a watering can with a spout.
Fertilization
Provide Silphium perfoliatum L. var. perfoliatum with a balanced fertilizer in the spring before new growth starts. Use a slow-release granular fertilizer, following the manufacturer's instructions for application rates. Alternatively, you can apply a top dressing of compost or well-aged manure. Avoid using high-nitrogen fertilizers, which can promote leaf growth at the expense of flower production.
Pruning
Cup plant does not require pruning, but you can deadhead spent flowers to encourage more blooms. Cut off the spent flower stalk near the base of the plant, just above a leaf node. Pruning can also be used to control the height of the plant and prevent it from flopping over in the wind. Cut back the stem by a third to half in the spring before new growth emerges.
Propagation Methods of Silphium perfoliatum L. var. perfoliatum
There are three main methods of propagating Silphium perfoliatum L. var. perfoliatum: seed propagation, root division, and stem cuttings.
Seed Propagation
Propagation through seeds is the most common method for Silphium perfoliatum L. var. perfoliatum. The plant produces seeds in late summer or early fall, which should be harvested when they are fully mature. After harvesting, the seeds should be stored in a cool, dry place until planting time in the spring.
Before planting, the seeds may require treatment with a stratification process that mimics winter conditions, which the plant needs to germinate. Sowing seeds in the fall can eliminate the need for stratification. The seeds should be sown 1/4-inch deep in a well-prepared seedbed, as it can take up to three weeks for the seedlings to emerge.
Root Division
Root division is an excellent option for mature Silphium perfoliatum L. var. perfoliatum plants that need to be divided or rejuvenated. The best time to divide roots is in early spring before new growth appears. Dig up the plant and separate the crown and roots into sections with sharp, sterile tools, ensuring each section has a good root system and some leaves. Replant each section in a prepared bed or pot immediately, and keep lightly watered until growth resumes.
Stem Cuttings
Stem cuttings are a less common propagation method for Silphium perfoliatum L. var. perfoliatum. Cuttings can be taken in early summer from mature stems that have not yet produced flowers. To take cuttings, snip a six-inch section of stem and remove the lower leaves before inserting the cutting into a well-draining rooting medium. Keep the cuttings moist, but not waterlogged, and cover them with a clear plastic bag or plastic dome to maintain humidity until roots form. Once roots form, transplant the cuttings into pots or the garden bed.
Disease Management
Silphium perfoliatum is susceptible to various diseases. Some common ones include:
- Rust: This fungal disease causes orange or reddish-brown pustules on leaves and stems. To manage rust, remove infected leaves or plants and treat with a fungicide.
- Leaf spot: This fungal disease causes dark spots on leaves. To manage leaf spot, remove infected leaves and treat with a fungicide.
- Verticillium wilt: This fungal disease causes wilting, yellowing, and eventually death of the plant. Unfortunately, there is no cure for verticillium wilt. To manage the spread of the disease, remove infected plants and avoid planting susceptible plants in the same area.
Pest Management
Silphium perfoliatum may also be affected by a variety of pests:
- Aphids: These small insects suck the sap from the plant and cause stunted growth and yellowing. To manage aphids, spray with an insecticidal soap or release natural predators like ladybugs.
- Japanese beetles: These beetles feed on the leaves, causing skeletonization of the foliage. To manage Japanese beetles, handpick them off the plant or use a pesticide.
- Cutworms: These caterpillars feed on the stem at soil level and can cause the plant to wilt and die. To manage cutworms, place a collar around the stem at soil level or use a pesticide.
