How to Grow and Care for Cup Plants

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, 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.

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. If you're wondering where the name "cup plant" comes from, look closely at the plant's 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 ample growing space and may overwhelm smaller plants. Although the cup plant can appear weed-like to some gardeners, it is well-suited for prairies, wildflower gardens, naturalized areas, or bordering a stream or pond.

Common Name	Cup plant
Botanical Name	Silphium perfoliatum
Family	Asteraceae
Plant Type	Herbaceous perennial
Mature Size	4-8 ft.
Sun Exposure	Full sun
Soil Type	Clay or wet soil
Soil pH	Acidic to slightly basic
Bloom Time	July to September
Flower Color	Yellow
Hardiness Zones	3-9 (USDA)
Native Area	Eastern-central Canada to southeastern United States

Cup Plant Care

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. Cup plants grown from seeds likely won't bloom until at least their second year of growth. During this period, keep the cup plant well-watered and free of weeds.

Fortunately, cup plants are generally resistant to serious insect infestations or diseases. Large crops of cup plants may be susceptible to the fungus Sclerotinia, but it's rare in gardens.

Light

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.

Soil

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.

Water

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 (last frost around May 15th and first frost around September 15th) to the very warm zone 9 (last frost date of March 1st and first frost date of December 15th).

Fertilizer

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 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.

Types of Cup Plants

There are two recognized varieties of the cup plant:

• Connatum (hairy stems; found in a handful of mid-Atlantic states)
• Perfoliatum (extremely common throughout the central and southern United States)

Propagating Cup Plants

Because cup plants are such vigorous and expansive growers, propagation is rarely a concern. If you would like to start a new patch of cup plants, simply dig up an existing plant and transplant it elsewhere in your landscape. Water well, and the plant should propagate itself.

You can also propagate cup plants from seed as described in the steps below.

How to Grow Cup Plants From Seed

The easiest time to start a crop of cup plants from seed is in late fall:

1. Sprinkle seeds on open soil, and gently press the seeds into the soil.
2. Cover the area with a light layer of straw to help retain moisture and prevent birds from eating the seeds.

If you'd like to plant in the spring, you'll need to stratify (chill ) the seeds for 60 days before planting:

1. Mix the seeds with moist sand and place them in a refrigerator or a cold location outdoors.
2. After 60 days, in early spring, plant your seeds and keep the soil moist to ensure germination.

FAQ

• Are cup plants invasive?

  Cup plants are native to the United States, so they are not technically invasive. They are vigorous growers, though, and they will tend to overtake areas of your landscape, including smaller plants, if not kept in check.

• How tall do cup plants get?

  Cup plants can grow as tall as 8 feet, making them a candidate for landscape edges, fence lines, or borders behind smaller plants.

• Are cup plants good for pollinators?

  Yes—like sunflowers, cup plants attract all sorts of pollinators like butterflies, bees, and moths. The flowers also hold water like little cups, so birds also come to cup plants to drink.

From: thespruce