Ranunculus bulbs can survive the winter in the ground under a few inches of organic mulch in USDA plant hardiness zones 8 through 11. However, in places where temperatures fall below -3.89 degrees Celsius, you must dig up ranunculus bulbs and store them indoors. Pull your ranunculus bulbs from the ground in late fall after the foliage yellows and dries out -- a sign it's going dormant -- and prepare them for storage. Once temperatures warm, just before the last predicted frost date in the spring, you can replant them outside.
Cut back the foliage to an inch or so above soil level.
Dig the bulbs out of the soil, taking care not to scratch or nick them. Bulbs with compromised skin probably won't survive storage.
Brush the soil off the tubers and lay them in a sunny spot until their surface dries completely.
Cover the tubers in a plastic container with at least 1 inch of dry peat moss on all sides. Do not stack the bulbs or allow them to touch one another.
Place the container in a dry area that remains consistently between 10 and 12.8 degrees Celsius. If you live in an area with high humidity, consider locating a dehumidifier in the room where you store the ranunculus bulbs.
Check the bulbs periodically for signs of mould or disease. Remove and compost any compromised bulbs as soon as possible to prevent the problem from spreading.
According to the University of Kentucky Extension Service, ranunculus bulbs are difficult to store. Some of the bulbs may not survive the winter even under ideal conditions.