Caltha is a species of 10 flowering perennials belonging to the buttercup, or Ranunculaceae, family of plants. It is also known as Marsh Marigold, because it prefers to live in a wet, swampy environment. Caltha plants grow as a wildflower throughout much of the Northern Hemisphere. All varieties develop large, rounded masses of heart-shaped leaves with clusters of bright yellow flowers that resemble the buttercup.
This plant is adaptable and tough, and will grow in just about any climate or soil, except where it is extremely dry. It will even survive with its roots completely immersed in water. While it thrives in full sunlight, it will tolerate partial shade in warmer areas. It is often one of the first plants to appear in cold-winter areas and flower in the very early spring. The blooming stage is usually followed by the entire plant going dormant for the rest of the year.
Its attractive, rounded shape and showy flowers means calthas are often planted as edging in gardens. They make good container plants, and also are popular in alpine and rock gardens. Calthas are toxic, so deer and other pests stay away from them. Calthas are a skin irritant and can cause rashes or skin blistering in sensitive people. Gloves should always be worn when in contact with these plants.
Caltha has a habit of spreading and can be hard to eliminate. The roots of these types of plants form into tangled, fibrous bunches that are not easy to remove. Any bit of root left in the ground will survive and grow, much like a weed. For these reasons it is recommended that undesirable plants be carefully dug up rather than pulled out of the ground.
Gardeners wishing to increase, rather than eliminate, their caltha plants can do so by dividing them. This is most easily done right after they have finished blooming in the spring, or in early summer, because once the plants go dormant they will disappear until the following year. Division also can be done in the fall, if the location of the roots was marked before the plant went dormant.
Caltha can be grown quite easily from seed. The spent flowers of the caltha plant form into spiky seed heads that should be collected as soon as they are dried and brown. Seed heads left too long on the plant will burst and the seeds will be widely scattered. This will result in hundreds of caltha seedlings the following growing season.