How To Grow And Care For Ranunculus (Persian Buttercup)

Ranunculus is a favorite amongst flower lovers for good reason. Also known as Persian buttercups (Ranunculus asiaticus), the ranunculus sold to gardeners and florists have delicately ruffled blooms that inspire comparisons to roses or double-petaled peonies. They are available in just about every color you could want and last a long time as a cut flower, making them a great choice for romantic arrangements or bouquets.

Ranunculus can be grown from bulb-like corms to flower during cool spring weather. Keep children and pets away from the bulbs and plants, as buttercups are toxic to people, dogs, cats, and horses. Once temperatures rise above 70°F, the button-like blooms begin to go dormant. For that reason, most gardeners grow ranunculus as seasonal spring flowers.

Plant Attributes

Ranunculus Care

The care of ranunculus can differ depending on your USDA hardiness zone. If you plant them in Zone 8 or warmer, they can grow as perennials, but they prefer mild and dry summers. Ranunculus are usually planted in fall or winter in warmer areas so they can bloom in early spring before the summer heat arrives. Unless you have a high tunnel or greenhouse, in cooler zones you should start the corms in a planting tray in early spring about four weeks before the last frost date. Regardless of when or where you plant them, ranunculus will need to be protected when frost is expected.

Ranunculus thrive in full sun and in organically enriched, well-drained soil. Gardeners can use raised beds if the native soil isn't conducive to growing. At the end of the season, let the plants die back. The bulbs in the ground prefer dry soil when dormant, so if you can’t provide that, it’s best to treat them as an annual. Regardless of where you live, the one thing you’ll want to monitor is the moisture level of the soil. If the ground is too wet, there’s a high chance that the plant will rot.

Light

Ranunculus require full sun, or at least six hours of direct sun a day, to grow and bloom best. In hotter climates, a little protection from afternoon sun can be helpful.

Soil

Plant ranunculus in loamy or sandy soil that is slightly acidic and has good drainage. Enrich the soil by mixing in compost. Ranunculus do not tolerate clay. If the ground conditions seem unfavorable, you can always plant ranunculus in raised beds for a more controlled environment.

Water

When first planting corms, soak them in water for up to four hours before planting. This will stimulate growth. The soil should be kept lightly moist when ranunculus are first sprouting and growing (see instructions for planting below under "Potting and Repotting Ranunculus.") After you start to see the new plants sprouting up, you can begin a regular watering routine. Ranunculus don't appreciate soggy soil, so don’t overdo it. Once the plants are more established, it’s always good to wait until the soil is a little dry before watering.

Temperature and Humidity

Ranunculus likes cool spring weather, but can't survive a hard frost. Protect your plants with frost cloth on cold nights or keep them in a cool environment around 50ºF (such as in a greenhouse, high tunnel, or sunny garage) until it's time to plant them outside.

Add mulch around the base of the plants to protect them from the summer heat. If you don’t, expect ranunculus to go dormant once temperatures exceed 90ºF or even sooner. If conditions are unusually hot and wet, the corms will rot and the plants will die.

When flowering tapers off and leaves start to yellow, stop watering the plants and allow the foliage to die back. Where tuberous roots are hardy in the ground, they can be left undisturbed as long as soil can be kept dry during summer.

Fertilizer

After the first few ranunculus leaves appear, you can begin a fertilizing routine. Deliver a slow-release fertilizer for flowers once a month, following the product label's instructions for best results.

Types of Ranunculus

This very large genus comprises several hundred species of widely differing habit and appearance. True Persian buttercup is native to Asia and the Mediterranean region and grows well in Zones 8–10. The tuberous-rooted plant can grow up to 2 feet tall and wide with fresh green, almost fern-like leaves. The hybrids bear one to four 3- to 5-inch wide, semi-double to double blooms that resemble a small peony bloom. Colors include whites, yellows, golds, pinks, reds, and purples. Here are a few of the most common types of ranunculus sold to gardeners:

• 'Tecolote': This series has large, 4-5 inch blooms in pastels, bold colors, and picotees, which are a solid color edged with a secondary color. Stems can reach 24 inches in height.
• 'Bloomingdale': The 'Bloomingdale' varieties offer a wide range of colors on dwarf plants that grow 10 to 14 inches tall and support large blooms on sturdy stems.
• 'Tomer': These varieties grow to 10 or 12 inches tall. Flowers are 2.5 inches across.

Pruning Ranunculus

There’s no need to prune ranunculus, but deadheading spent blooms as they fade will redirect the plant’s energy to produce more blooms.

Propagating Ranunculus

Dividing the ranunculus bulbs can help you control the size of the plants and tidy your garden bed. If you live in Zone 8 or above, dig up corms with a shovel and divide them with a sharp knife. Plant the new divisions with roots facing down. Below Zone 8, ranunculus is considered an annual.

Some gardeners dig plants up when foliage turns yellow; cut off the tops; let roots dry for a week or two; and store them in a cool, dry place until planting time. But because corms don't store that well, most people find it simpler to discard the plants and set out new corms when the time comes.

How To Grow Ranunculus By Seed

You can purchase ranunculus seeds or collect your own. As your ranunculus flowers begin to fade, pinch off the flower and put them in a brown paper bag to dry. In a week or two, you can give the bag a good shake to harvest the tiny seeds. Ranunculus seeds take three or four months to grow into a blooming flower, by which time the weather may be too hot for them to thrive. Start them in winter to get a head start, following these steps:

1. Fill a tray with moistened, sterile potting soil.
2. Sow the seeds over top of the soil and press them gently into the soil to make contact.
3. For the best germination, place the tray in a location that is between 50-60°F. Ranunculus seeds need light to germinate, but keep the tray out of direct sunlight.
4. Keep soil moist and seeds should sprout in 14-28 days. After the plants have a few leaves, you can transplant them in containers and gradually harden them off outdoors, but they must be protected from spring frost.
   

Potting and Repotting Ranunculus

If you’re growing ranunculus as an annual, planting them in a container garden or raised bed is a good way to enjoy these pretty flowers. Fill your pot or raised bed with an all-purpose potting mix that is well-draining and includes compost or other organic matter.

If you are planting corms, soak the corms in water up to four hours before planting to stimulate growth. Set corms in soil with prongs down, 1-2 inches deep and 6–8 inches apart. Water thoroughly, then withhold water until leaves emerge or soil starts to dry. Sprouts should appear in about two weeks. If you started your plants indoors, they can be moved to the garden now, covering or moving to a protected spot when you expect a frost.

Common Pests & Plant Diseases

Birds are fond of ranunculus shoots, so protect sprouting plants with netting or wire. Or start plants in pots or flats, then set them in the garden when they're 4-6 inches tall (a size that will be less appealing to pesky birds.) Deer do not bother them. Aphids may be controlled with insecticidal soap or horticultural oil.

Excess humidity and watering can lead to bacteria, fungi, or powdery mildew infecting the leaves. Avoid watering in the evening and reduce watering if needed. Improve air circulation if possible. A serious powdery mildew problem can be treated with an appropriate fungicide.

How To Get Ranunculus To Bloom

Flowers appear about 90 days after planting and usually last four to six weeks. Ranunculus need sunlight for a good bloom, but warm temperatures can bring blooming to a halt. Once temperatures exceed 70°F, flower buds may stop forming. A shade cloth or moving your plant to a more sheltered area could help delay dormancy.

Common Problems With Ranunculus

Yellow Leaves

Yellow leaves can be caused by too much moisture, not enough sunlight, or the plant going dormant in summer. Adjust soil texture, moisture, and sunlight if needed.