Silphium perfoliatum | Cup Plant
The Cup Plant, also known as Carpenter’s Weed, Indian Cup, Rosin Weed, and Ragged Cup, is a towering, showy sunflower-like perennial with a native range from eastern-central Canada to the southeastern United States. It is most commonly found in low woods, prairies, meadows, and bordering streams or ponds. It’s an extremely hardy, low-maintenance plant that can survive in a variety of temperatures and locations. It establishes well in average garden soil or in heavier, wetter soils. It’s a large plant that requires ample growing space. If you like large, robust specimens, this plant is for you! The root system consists of a long central tap root and many shallow rhizomes. The rhizomes help to spread the plant, forming substantial colonies over time. Although the cup plant can appear weedy to some folks, it’s well-suited for prairies, wildflower gardens, naturalized areas, or for bordering a stream or a pond.
Silphium perfoliatum is known for it’s bright yellow daisy-like blooms, coarse leaves, and long stems. The name “cup plant” (perfoliatum) comes from the shape of the leaves that clasp the main stem, making it look like the stem has pierced through them. The joined leaves form a small basin that enables them to hold water. It’s not uncommon to see birds or insects sipping water from the small pools on a hot day during the growing season, which is July through September. Pollinators are attracted to the large, bright yellow blooms, and birds enjoy the nutritious seeds too.
If starting seeds indoors, Cup Plant seeds will require a 60 day period of cold-moist stratification before the seeds will germinate. Or if you plan on starting them outdoors you can sow the seeds in the fall and let nature take care of the stratification.
Cold stratification is a term for a procedure that can improve certain seed germination rates by 300-400%. Cold stratification is designed to mimic the winter season’s cold and moist weather that unlocks a seeds protective germination mechanisms and triggers the seed to sprout out of its dormant state. (Most perennial plant seeds (such as native wildflowers) require this combo of cold and damp to germinate.) In nature, this occurs naturally, but by doing the process yourself in a controlled environment, you keep the young seeds safe from any animals that might eat them and they’ll also be less likely to succumb to rot or mildew, leaving more seeds to grow.
There are many methods to cold-stratify seeds, but the two key factors are always moisture and cold. The best and easiest way is to put a small amount of moist/wet sand/soil in a zip baggie and store in the refrigerator for 2 months time (or more). Once stratified, surface sow the seeds (and sand) and gently press into the dirt. Germination will occur with heat humidity and light indoors, or if outdoor, once spring temps and sunlight are adequate. Be sure to plant stratified seeds within a day or so after removing them from the refrigerator because as soon as they warm up they will be ready to grow and may start to sprout.
Sun exposure: Full sun
Mature height: 8-10 ft
Mature width: 4-5 ft
Hardiness zones: 3-9
*Please note: We cannot ship Silphium perfoliatum Cup Plant seeds to Connecticut, New Hampshire, and New York at this time. Checkout is disabled for this product in these states.