Ranunculus, a genus from the Ranunculaceae family, is a collection of over 400 species of molded blooms in shades of gold, red, orange, pink, purple and white referred to as the Persian Buttercup. These frost-tolerant perennials grow best in southern locations that experience mild winter and a long spring season; however, ranunculus grows successfully in colder climates when planted in late winter or early spring. Popular varieties, such as Tecolote, create beds of color when planted en masse and provide beauty to cut flower arrangements.
Ranunculus bulbs require at least six weeks of cool temperatures to properly sprout and bloom. In warmer climates, it's best to start tubers indoors in January or February and then plant out in early spring. The roots can tolerate temperatures as low as 10 degrees F, while the foliage can withstand 20 degrees F.
In cooler climates (zones 8 to 11), plant bulbs in early to mid fall for late winter and early spring blooms. In warmer climates, plant bulbs in late winter or early spring, at least two weeks before the last expected frost, for early summer blooms. In zones 4 and 5, plant bulbs outside in mid-May. In zones 6 and 7, bulbs should be planted in mid-April.
The Right Grade
Ranunculus bulbs are separated into four grades, based on the size of bulb. Jumbo bulbs can produce up to 35 flowers per bulb, while #1 bulbs produce 20 blooms, #2 bulbs sprout over a dozen and #3 bulbs provide less than a dozen. Jumbo and #1 bulbs are well-suited for container and pot planting; #1, #2 and #3 bulbs are better for mass plantings in beds and borders.
Well-draining soil is the most important factor in determining where to plant ranunculus. These sensitive tubers do not tolerate consistently soggy soil or standing water. Excess moisture and excess warmth will quickly induce decay. Clay soil should be amended with organic compost, peat and sand to improve drainage. In addition to good drainage, full sunlight is also needed for ranunculus plants to thrive.
Ranunculus tubers should be watered thoroughly at planting, covered with a layer of mulch, compost or straw and then left alone until sprouts emerge, typically within 15 to 20 days. Water lightly during the growing season, no more than 1 inch per week, and increase to twice per week during periods of drought. For perennial ranunculus plants, stop watering once the blooming ceases for the season, to prevent tubers from rotting during the heat of summer.
Start out with nutrient rich soil with a pH level of 5.5 to 6.5. Adding organic materials or compost will improve the nutrient levels of the site. While ranunculus does not require regular feedings, 10-10-10 liquid fertilizer can be applied, according to manufacturer's directions, at planting and during the growth process to encourage fuller blooming. Stop feedings after the bloom cycle to prepare the tubers for dormancy.
Ranunculus tubers resemble a tiny bunch of bananas, and should be placed in the soil with the banana-shaped bulbs pointing downward, at a depth of 1 to 2 inches below soil level, depending upon bulb grade. Grades jumbo, #1 and #2 should be spaced 8 to 12 inches apart, while #3 tubers should be placed roughly 4 inches apart. When planting jumbo-grade tubers in containers, one or two tubers will fill a 10-inch pot and allow for sufficient root development.
After the Blooms Fade
Once the blooming season comes to a close, foliage can be left in the landscape for the remainder of summer. At the end of the growing season, when foliage dies off, tubers can be dug up and stored for the next season, or left in the ground to decay, if being used as annuals. In warmer climates, perennial ranunculus tubers may be left in the ground as long as the soil remains dry or only slightly moist. Allow the foliage to die back, then cut it off at ground level and allow the tubers to rest until the next growing season.