The common European marigold, (like the Mexican variety), is justly popular because it is easy to grow, and pests don't like it. It was first mentioned by the old-time herbalists in 1578, quote, "It has pleasant and bright shining yellow and orange single-petal flowers." 

It was used by herbalists during the times of ancient plagues, and the petals of the flowers were dried and sold for use in making broth in the winter. The flowers have also been used to add yellow color to cheese in times past.

Native to southern Europe, the seeds can be sown directly into the soil and germinate easily in sun or part sun. Plants begin to flower in June and continue till frost. Gather seeds when they ripen in August and September.

Some people use the flowers to treat the stings of wasps and bees and also to treat warts. Large flowering marigolds (those that originated in Mexico) are usually yellow or orange, and French marigolds are smaller and orange/brown in color.

All types of marigolds last well as cut flowers, but it is best to remove all of the leaves below the water line in a vase as they otherwise develop an unpleasant odor.

Marigolds are excellent plants for children to grow when they begin gardening as they are likely to grow well even with sporadic watering.

Note: 

The European variety (about 20 species) is daisy-like in appearance, and the botanical name is Calendula officinalis with the common name of Pot marigold or English marigold. The name calendula comes from the same root as the word "calendar," signifying that it blooms almost all year in zones 6-10.

The Mexican variety is larger and many petaled, and its botanical name is Tagetes, and they are unrelated to the European varieties.