How To Plant Ranunculus
Planting Method for Ranunculus
Depending on where you live and the type of garden or landscape you have, you can plant your ranunculus corms in either fall or late winter/early spring, in an area that gets full sun. Corms can be planted in the fall and successfully overwintered outdoors with protection from a low tunnel or frost cloth in areas with mild winter temperatures (USDA zone 7 and above). Ranunculus must be grown in a minimally heated hoop house or held back and planted out at the end of winter/early spring in colder areas (USDA zone 6b and below). Corms that are exposed to temperatures below 25°F (-4°C) will freeze and eventually rot once thawed. So make sure to keep them away from extreme cold temperatures.
When you unpack your corms, you’ll notice that they look like little brown creatures (octopus or alien?), which is probably not what you expected for the beautiful flowers they produce. Don’t worry, these weird little, hard squigglies will produce an abundance of beautiful blooms in the spring.
Soak your corms in room temperature water for 3 to 4 hours before planting. It is critical not to oversoak them; otherwise, they will rot. This allows the corms will plump up and often double in size as they soak. Corms can be planted directly into the ground, or pre-sprouted after soaking in a greenhouse or protected area. Flowers will bloom a few weeks earlier if the corms are sprouted before planting.
Fill a flat-bottom seed tray or pot halfway with moist potting soil to pre-sprout. Sprinkle the soaked corms on top of the soil and cover them completely with more soil. Place this tray in a cool place (40°F-50°F / 4°C-10°C) where rodents cannot find it for 10 to 14 days. Every few days, check on the corms to ensure that the soil is moist but not soggy, and remove any corms that show signs of mold or rot.
Corms will swell to about twice their original size during this time and develop little white rootlets that resemble hair. When rootlets appear, they are ready to be planted in the ground. It is critical to prepare the growing beds before planting. We mix in a generous amount of compost (2-3 in) and a balanced organic fertilizer. With 4 rows per bed, ranunculus corms are planted 9 in (23 cm) apart at a depth of 2-3 in (5-7.6 cm). Plant corms with the little root legs pointing down.
Cover the plants with frost cloth during cold spells when temperatures fall below freezing. Corms planted in autumn bloom in early spring, while corms planted in late winter/early spring bloom in mid-spring.
We are frequently asked how to store ranunculus corms until planting time, and whether they can be left in the ground to rebloom the following year. Corms can be stored in their original bags in a cool, dry place until planting time. In colder climates, grow ranunculus as an annual and replace the corms every season. If you live in USDA zone 7 or higher, you can leave your corms in the ground and they may bloom the following year, depending on a variety of factors including how cold your winter is, how well your soil drains, and how much pest pressure you have in your garden. I never rely on overwintered corms and always plant new ones. If the overwintered ones return, you have the luck of the Irish.
Ranunculus has an exceptionally long vase life, often exceeding 10 days. For a vase life of 10 to 12 days, cut when the buds are colored and squishy like marshmallows but not fully open. If the blooms are open when cut, they will still last for a week but will be more difficult to transport. To encourage new blooms, cut spent flowers down to the ground.