Marsh Marigold Care: How To Grow Caltha Palustris

Caltha Palustris [KAL-tha pal-US-triss] (Caltha palustris L) is a wildflower belonging to the Persian buttercup family (Ranunculus and Ranunculaceae).

The Marsh Marigold is no relation to the actual marigold plant, which is a member of the Aster family.

The Yellow marsh-marigold is a mounded perennial in Canada and North America native to wet meadows, swamps, marshes, fens, and stream margins from Newfoundland to Alaska south to Nebraska, Tennessee and North Carolina.

Yellow flowering Caltha PalustrisPin

The plant’s genus name, Caltha, is derived from the Latin, calendula, meaning a plant with yellow flowers.

The specific epithet, palustris, is Latin for marsh-loving.

Common names include:

  • Marsh Marigold
  • King Cup
  • Cowslip

Marsh Marigold Care

Size & Growth

The plant attains a height and spread of 12″ – 18″ inches.

Cowslip’s stems are hollow with thick green glossy leaves.

Round or kidney-shaped leaves may be as large as 7″ inches across.

They are deeply heart-shaped at the base.

The leaf edges are usually scalloped but may be toothless.

Lower leaves are often larger because they are more mature than the higher leaves.

Upper leaves are younger and smaller.

Flowering & Fragrance

Marsh Marigolds’ flowers look very much like common buttercups.

Its primary bloom color is yellow.

The bright yellow flowers with petal-like sepals, thick ring of abundant stamens, and a cluster of carpels in the center bloom in early spring.

These flowers transition into fruit called a follicle.

This is a curved capsule approximately 3/8″ of an inch long.

The fruit starts out green and then dries, matures into a seed pod, turns brown and splits open to disperse seeds.

Light & Temperature

Plant Marsh Marigold in partial shade to full sun.

For the most abundant flowering, choose full sun. However, if your area is subject to harsh, hot, punishing sunlight in the partial summertime shade is preferred.

King Cup may go dormant during the summer time.

USDA plants hardiness zones of 3 – 7.

Watering & Feeding

This plant likes very moist soil.

Fertilizing is not usually necessary.

Soil & Transplanting

Soil similar to the natural, rich, boggy soil moisture found in the plant’s natural habitat is best.

If transplanting from a natural setting to your pond side, rain garden, bog garden or marsh, take note of the plant’s natural environment and strive to duplicate it.

Grooming & Maintenance

Trim off dead leaves and flowers.

No regular pruning or maintenance is needed.

How To Propagate Caltha Palustris

The plant will spread on its own via rhizomes and seeds.

  • Dig up clumps of King Cup and separate the rhizomes to transplant.
  • Place cloth bags over the seed heads to stop the dispersal of the seeds to collect them.
  • Plant them in your chosen location.

Cowslip Pest or Disease Problems

This water-loving plant is not subject to significant attacks by insects.

In some circumstances, it may have problems with rust and powdery mildew. Learn more on How To Treat Powdery Mildew.

Is Cowslip Toxic or Poisonous?

Some parts of the plant are edible with care when cooked.

Eating the plant raw can cause poisoning.

The plant contains protoanemonin, a substance if eaten in large quantities causes:

  • Convulsions
  • Burning of the throat
  • Vomiting
  • Bloody diarrhea
  • Dizziness
  • Fainting

Is Cowslip Invasive?

This plant is not considered invasive.

Suggested Uses For King Cup

Marsh Marigold is an excellent choice for a water garden, a bog garden, along the verges of a pond or stream or to naturalize in low-lying areas.

Substitute capers with pickled and cooked flower buds from this plant.

Cook the young leaves as greens; however, you must take care to boil them thoroughly, and you should never eat any part of this plant raw as it’s toxic.

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