Ranging between four and eight feet tall, the cup plant (Silphium perfoliatum) is a sunflower-like perennial with coarse leaves that's commonly found in low woods, prairies, and meadows, and bordering streams or ponds. It's an extremely hardy, low-maintenance plant that can survive in a variety of temperatures and locations, and has the ability to self-seed.
The cup plant's native range demonstrates its hardiness, ranging from eastern-central Canada to the southeastern United States. Cup plants grown outside of the native range are considered invasive, and may overwhelm smaller plants even when grown within its native range.
Known for their yellow blooms, coarse leaves, and super long stems, cup plants attract butterflies, birds, bees, and other beneficial insects throughout the growing season, or July through September. Pollinators are attracted to their large, bright blooms, while birds enjoy to eat the plants' nutritious seeds. If you're wondering where the name "cup plant" comes from, look closely at the plants leaves—they form a small basin that enables water to pool around the stem. It's not uncommon to see birds and other animals or insects sipping water from these tiny basins on a hot day.
The cup plant is a large plant that requires growing ample space, so you may want to consider another plant if you have a smaller garden or plants that could become overwhelmed by the cup plant. Although the cup plant can appear weed-like to some gardeners, its well-suited for prairies, wildflower gardens, naturalized areas, or bordering a stream or pond.
|Botanical Name||Silphium perfoliatum|
|Common Name||Cup plant|
|Plant Type||Herbaceous perennial|
|Mature Size||4 to 8 feet|
|Sun Exposure||Full sun|
|Soil Type||Clay or wet soil|
|Soil pH||6.6 to 7.5 or 7.6 to 7.8|
|Bloom Time||July to September|
|Hardiness Zones||3 to 9|
|Native Area||Eastern-central Canada to southeastern United States|
How to Grow Cup Plants
Because many gardeners and gardening centers consider the cup plant weed-like, growing your plant from seeds is recommended—it may be difficult to find a plant in your local garden center. It's easiest to start from seed by planting outdoors in the fall, but planting in the spring is possible, too. Just be sure you'll have a full 60 days of cold stratification before sowing the seeds. It's important to note that that cup plants grown from seeds likely won't bloom until at least its second year of growth. During this period, keep the cup plant well-watered and free of weeds.
Fortunately, cup plants are not very susceptible to serious insect infestations or diseases. Large crops of cup plants may be susceptible to the fungus Sclerotinia, but it's rare in gardens.
Although cup plants are extremely hardy, six to eight hours of full sun is recommended for optimal growth. If full sun isn't available, the cup plant can thrive in partial sun, too. If you live in a colder zone, consider planting your cup plants in a spot with full sun and little to no wind.
Because the cup plant has a large native range, it can grow in a variety of soils, but best tolerates medium-to-wet soil, or soil rich in clay. If you want to achieve taller cup plants; plant them in wetter soil; if you want shorter cup plants, drier soil is best.
The cup plant can tolerate heat and drought, but prefers regular watering. Be careful not to overwater your cup plants.
Temperature and Humidity
As previously mentioned, the cup plant is extremely hardy and can grow in a variety of climates and locations. Its growing zones range from the cold zone 3 (with a last frost around May 15th and first frost around September 15th) to the very warm zone 9 (which has a last frost date of March 1st and first frost date of December 15th).
Thanks to its hardiness, commercial fertilization isn't required for cup plants in gardens, prairies, or naturalized areas. If you want to give your cup plants additional protection, opt for compost or composted manure as a drop dressing on the roots.
In larger crops, fertilizing is recommended as early as possible during the first year of the cup plant's growth in order to protect the roots. Some studies of larger cup plant crops have shown that fertilizing is not required in the cup plant's second year.
Varieties of Cup Plants
There are two recognized varieties of the cup plant: connatum, which has hairy stems and is found in a handful of mid-Atlantic states, and perfoliatum, which is extremely common throughout the central and southern United States.