Caltha plants are hardy perennials that reach a maximum height of about 30 cm.
They are also known as Cowslip or Marsh Marigold.
They have buttercup-like flowers of yellow, pink or white and flower in the spring time.
Caltha palustris (Yellow Marsh Marigold) by Blumenbiene.
Caltha leptosepala (White Marsh Mallow) by Brewbooks.
Common Names: Marsh Marigold, Cowslip, Kingcup.
Life Cycle: Hardy perennial.
Height: 10 to 30 inches (25 to 75 cm).
Native: Wet and temperate regions of both hemispheres.
Growing Region: Zones 4 to 10.
Flower Details: Yellow, white, pink. Buttercup-like.
Foliage: Herbaceous. Heart-shaped. Kidney-shaped. Waxy. Smooth, winkled or toothed edges. Green.
Sow Outside: Cover seed. Early summer from fresh seed. Use Peat pots atop a saucer of water. Germination time: one to three months. Transplant peat pots into the garden proper in the middle of the summer. Spacing: Small species, 8 to 10 inches (20 to 25 cm); Mid-sized 18 inches (45 cm); Larger species 24 to 40 inches (60 to 100 cm).
Sow Inside: No.
Requirements: Full sunlight or partial shade. Soil pH 5.0 to 7.0. Clay, moist soil, wet soil. Regular watering to ensure that soil is always damp. Propagate: by dividing in the autumn, or following flowering in cooler areas.
Caltha should be grown outdoors in peat pots from fresh seed in the summer.
The seed of cowslip should be lightly covered and germination will take anywhere from between one to three months.
Once seedlings have grown in the peat pots they should be transplanted in the middle of summer, with a spacing of about 50 cm (20 inches).
As they prefer sun and shade at different times of the growing season, it is probably best to grow them in areas of partial shade. They prefer a moist to wet clay soil of pH 5 to 7.
It is important to keep the soil where Caltha grows very moist throughout the year.