One of the most brilliant of the spring-blooming bulbs, ranunculus (Ranunculus spp.) have 3- to 6-inch flowers in almost every colour imaginable, even bi-colours. The frilly blooms grow on 12- to 18-inch stems; doubled types resemble miniature peonies. Purchase the largest tubers you can find for the showiest flower display.
The correct time to plant ranunculus depends on where you live and whether you're planting them in the ground or in containers. Ranunculus are ground-hardy only in warm areas, although they'll do well in U.S. Department of Agriculture zone 8 winters if mulched. In those areas, plant the roots when available in the fall, usually October or November. Elsewhere, they are either grown as potted plants or treated as a tender bulb and planted in the garden in the spring, as you would gladioli.
Outdoor Planting Where Hardy
Find a site in full or afternoon sun. Soak the tubers for an hour to hydrate them fully. Plant them 3 to 6 inches apart in well-drained soil with the claws pointing down and cover them with 1 to 2 inches of soil. Keep the soil around them moist but not wet and deadhead them as the flowers fade to encourage more blooms. Ranunculus will continue to bloom as long as the weather stays cool. The tubers can be left in the ground year-round in zones 8 and warmer. Mark their location so that you don't damage the tubers while they're dormant.
Outdoor Planting Where Not Hardy
Ranunculus need cool air temperatures to thrive and will stop blooming and go dormant when warm weather arrives. For best results the tubers should be started indoors 12 weeks before the last expected frost date for your area. Soak the tubers for an hour, then plant them 1 or 2 inches deep in containers and water well. Grow them in bright light in a spot that stays 15.6 degrees Celsius during the day and -12.2 to -9.44 degrees C cooler at night. Move the started bulbs to the garden right after the last frost date. After the plants go dormant, dig them up and allow them to dry, then store them in paper bags until it's time to start them again the next spring.
To plant ranunculus in containers, use one or two large tubers in a 10-inch pot. Soak the dried tuber for an hour before planting. Fill the pot with potting soil, place the tubers claw-side down and cover with 1 to 2 inches of soil. Water well and place the pot in a well-lit, 60 degree area. Unless the soil dries out, don't water again until leaves appear. Feed the plants every two weeks with a water-soluble houseplant fertiliser. Grow ranunculus indoors as a houseplant or set them outside after frost.
A Word of Caution
Ranunculus plants contain poisonous compounds, so use care. Ingesting any part of the plant causes pain, vomiting and diarrhoea. Handling the plant can cause skin irritation. Although the chances of a toxic reaction are low, always use gloves when handling the plant and use ranunculus with caution in gardens accessible to pet and children.