For impressive but delicate flowers, few plants can top a ranunculus plant (Ranunculus spp.), which produces brightly colored flowers with petals that resemble crepe paper. The genus contains several species, but the variety called Persian buttercup (Ranunculus asiaticus) is most commonly cultivated. The word "Ranunculus" comes from a Latin term meaning "little frog." Traditionally, when given as a gift, the flower proclaims the giver considers the recipient dazzling and charming. Also called Coyote's eyes, legend says that the flowers were used by a mythological coyote to replace his eyes after they were stolen by an eagle. In a home garden, it needs only good moisture and proper lighting to thrive and cover itself with showy flowers.
Ranunculus plants grow from fleshy roots called tubers that resemble small, elongated potatoes. They're resistant to frost and grow as herbaceous perennials, which die to the ground in winter and return in spring. The most common type, the Persian buttercup, grows in U.S. Department of Agriculture plant hardiness zones 8 through 11. It can withstand temperatures as low as 10 degrees F in colder parts of its range, although they do best where winters are mild and spring tends to be long and cool. The plant becomes a 6- to 12-inch-wide mound, with green leaves similar to those on celery; flowers develop on straight stems that are about 18 inches tall.
Two other ranunculus plants are also cultivated: creeping buttercup (Ranunculus repens, USDA zones 4 through 9) and lesser celandine (Ranunculus ficaria, USDA zones 4 through 8). These plants both have small, bright yellow flowers that resemble buttercups on low-growing, spreading plants that can become 1 to 3 feet wide. Although attractive plants, they can be invasive in some areas and might spread into naturalized areas by putting down new roots wherever stems touch soil. Only grow these types if you regularly cut back stems to prevent uncontrolled spread.
If you live within USDA zones 8 through 11, plant Persian buttercups in fall for flowers that appear in early spring, usually in March or April. In colder areas outside this range, plant tubers in spring, about a week before your expected last spring frost, and they'll generally bloom in late spring. In these colder areas, you can lift the tubers in fall, clean them of soil and store them in a paper bag in a cool, dry area until the next spring; you can also grow the plants as annuals.
Plant Persian buttercups in well-drained soil, amending it with an inch or two of compost to increase its fertility. Choose a spot in full sun for the most flowers, planting tubers about 2 inches deep and 4 inches apart. The tubers are in clusters resembling tiny bananas attached to a stem, so plant them with stems facing upward.
Persian buttercups also thrive outdoors when planted in containers, either alone or in a mixed grouping. Use commercially available potting soil and only choose a pot with at least one drainage hole; to avoid fungal problems, never let the pot sit in a water-filled saucer. The tubers develop large root systems, so a 10-inch pot suits two or three tubers, depending on their size.
For best flowering, keep a Persian buttercup's soil evenly moist, providing water whenever it's dry to the touch. When flowering ends, allow the foliage to remain on the plant, letting it die back naturally; once leaves fall, withhold water until the following spring when you see new growth. For a potted plant, keep it in full sun and water the soil when its top feels dry.
This plant doesn't require fertilization, but feeding every two weeks can enhance flower number or size. Use a water-soluble formula such as 10-30-20, diluting it at a rate of 1/2 teaspoon per gallon of water, and using it in place of a regular watering. Also check your product label for further directions.