Considered tender perennials, ranunculus plants grow best in areas with mild winters. They are deemed hardy to zone 8. Ranunculus tubers should be planted 2 inches deep. Spacing depends on the bulb size, with smaller bulbs planted 4 to 6 inches apart and jumbo bulbs spaced 8 inches apart. Tubers should be planted claw end down, in well-drained soil and full sun.
In zones 8 through 11, bulbs planted in the fall begin to flower in March. Pinching off faded blooms encourages more blooms.
North of zone 8, tubers should be planted in the spring just before the last expected frost. Blooming time for these bulbs is June through July. In these zones, tubers can also be started indoors in February. Plants can be transplanted outside after all danger of frost is past. Starting plants indoors ensures that blooming occurs before summer's high temperatures and humidity begin. North of zone 8, treating ranunculus plants as annuals works best since they do not survive a winter in the ground and tend to rot if they are dug up and over-wintered.
Ranunculus plants are part of the family Ranunculaceae, or the buttercup family. Ranunculus asiaticus, or Persian buttercups, produce brilliantly colored blooms that contain hundreds of petals, resemble cabbage roses and are a popular choice for gardeners.