The Persian Buttercup, or Ranunculus asiaticus, is a flower prized by gardeners for its layered, colorful blooms that resemble miniature peonies. Successfully cultivating these flowers depends heavily on planting time. Unlike many garden favorites, the correct starting date for Ranunculus is not a fixed calendar day but depends on the specific climate and hardiness zone. Getting the timing right ensures a lush spring display.
Understanding Ranunculus Corms
Ranunculus are grown from corms, which are underground storage organs similar to bulbs. These corms arrive in a dried, dormant state and have a distinctive, shriveled appearance often described as resembling a small octopus or claw. The corm serves as the plant’s food and water reserve, which it uses to break dormancy and begin initial growth.
For the corm to activate and thrive, it requires consistently cool soil temperatures, ideally \(40^{\circ}\text{F}\) to \(50^{\circ}\text{F}\). They are sensitive to heat; soil temperatures exceeding \(70^{\circ}\text{F}\) will cause the plant to shut down and go dormant prematurely. The growing season aims to maximize the cool period before the summer heat arrives.
Planting Timing in Cold Climates
Gardeners in cold regions, generally USDA Zones 7 and colder, must adopt a strategy to circumvent the risk of the ground freezing solid, which would kill the corms. The most reliable method is pre-sprouting, or chitting, which involves waking the corms up indoors before planting them out. This process should begin approximately four to eight weeks before the average last expected frost date.
To pre-sprout, corms are placed in trays of moist potting mix and kept in a cool location, maintaining temperatures around \(40^{\circ}\text{F}\) to \(50^{\circ}\text{F}\). This environment encourages the corm to develop robust root systems and small shoots without exposure to severe outdoor temperature swings. Once sprouts emerge and roots are established, the young plants are ready to be moved outside.
The goal is to transplant the established seedlings into the garden shortly after the last hard frost, when the soil is workable but still cool. Before final planting, the young plants must be hardened off by gradually exposing them to outdoor conditions. This slow acclimation prepares them for the full sun and breezes, ensuring a strong start.
Planting Timing in Mild Climates
In milder regions, typically USDA Zones 8 and warmer, Ranunculus can be planted directly into the garden in the fall. These areas mimic the plant’s native Mediterranean climate, offering the long, cool, and moist period the corms need to establish roots over winter. Corms should be planted between September and December, once the extreme summer heat has broken and cooler weather begins.
Fall planting allows the root structure to develop slowly over the winter months, resulting in strong plants and an earlier bloom period in late winter and early spring. The plants can tolerate mild frosts, especially when covered with a layer of mulch or frost cloth. Planting too late in the spring often means the plant will bloom only briefly before rising summer temperatures force it into dormancy.
Preparing and Sowing Ranunculus Corms
Regardless of whether they are destined for an indoor tray or a garden bed, all Ranunculus corms must first be rehydrated to break their dormancy. This is achieved by soaking the dried corms in room-temperature water for three to four hours before planting. Do not exceed this soaking time, as over-saturation can cause the corms to rot.
After soaking, the corms will have plumped up and are ready for planting. They must be oriented in the soil with the claw-like points facing downward, as roots emerge from this point. Plant the corms between one and three inches deep and space them approximately four to six inches apart to allow for adequate air circulation. Ranunculus require well-draining soil to prevent the corms from sitting in excess moisture and rotting.