With their delicate, tissue paper-like blooms and finely cut leaves, ranunculus (Ranunuculus spp.) are a stunning group of plants that brighten up a border, bed or bouquet. These frost-tender perennials often do not survive to flower another season because their bulb-like tubers usually rot in warm, wet summer soil unless dug up and stored carefully until the following spring.
Ranunculus are hardy in U.S. Department of Agriculture plant hardiness zones 8 to 11. Tubers can tolerate temperatures as low as 10 degrees Fahrenheit, while actively growing plants can handle brief periods of temperatures below 20 degrees F. For best flowering and vigor, plant in a location with full sunlight.
Use Well-Draining Soil
Ranunculus require an excellently draining, moderately moist soil. If your garden is prone to flooding or has poorly draining soil, consider planting ranunculus on a slope or a raised bed. Increase drainage by loosening up soil with a shovel before planting with a shovel and adding compost or organic matter.
Water after planting, and mulch with a thin layer of organic matter such as bark, straw or coco hulls. This will help retain some coolness and moisture in the soil. Ranunculus are prone to root rot in wet conditions, so unless the soil dries out, do not water again until you see sprouts.
Fertilize in the spring with a 10-10-10 fertilizer, diluting 6 tablespoons of fertilizer into 1 gallon of water. Thoroughly drench the soil around the plants, taking care not to splash the leaves.
Care After Flowering
Ranunculus blooms usually fade by summer. After flowering, prune off spent flowers or dead, wilted leaves. Do not prune off green leaves because they still supply vital nutrients to the roots. Once the plant goes dormant in late summer, leaves will turn yellow. Prune all remaining foliage at this point and stop watering the plant. Disinfect pruning equipment afterward by soaking it for five minutes in a solution that is equal parts alcohol and water. Rinse with water and air dry.
If left in the ground, even where hardy, tubers often rot before they have the chance to flower again. After you've cut back dried, dormant plants, save tubers for the following spring. Dig up tubers, cut off the tops and store them in a cool, dry place.
Replant in the spring after frosts have passed, spacing jumbo varieties 8 to 12 inches apart and small varieties about 4 inches apart. When planting tubers, plant 1 to 2 inches deep with the fleshy, claw-like Ranunculus end of the tubers facing down. Plant tubers shallower in heavy clay soils and deeper in loosely draining soils.