How to Grow Ranunculus

What you are planting

Garden ranunculus, also called Persian buttercup (Ranunculus asiaticus), comes from the eastern Mediterranean. It grows from a corm, a swollen storage stem that is sold dry and looks like a shriveled claw or a tiny octopus. Clemson notes it is sold with spring bulbs though it is not a true bulb. Size matters. Alaska Master Gardeners point out that bigger corms produce more flowers, so buy the largest you can find.

The plant is a cool-season perennial that is hardy only in about zones 8 to 10. Below about 28°F the plants are injured, according to NC State Extension. Below about 25°F the plant dies or the corm freezes and rots, according to Alaska Master Gardeners. That cold limit, together with the plant’s dislike of heat, decides when and how you plant.

Soak first

Soak the corms in room-temperature water for 3 to 4 hours before planting. They roughly double in size as they rehydrate. Alaska Master Gardeners leave the tap running slightly to keep the water fresh. Do not soak longer than 4 hours, because waterlogged corms rot. Clemson notes that soaked corms sprout quickly and flower more evenly.

Planting in mild-winter areas (zones 8 to 10)

Plant in fall so the plants root and grow through the cool months. Texas A&M AgriLife in Travis County (Austin) plants in October, and those plants bloom in April and May. Solano County Master Gardeners in California plant in fall but note that late-winter planting also works. In the Phoenix area, University of Arizona’s chart shows planting in October and November or from February into mid-March, with blooms from mid-February into May.

Plant the corms 2 inches deep with the claws facing down. Spacing advice varies: Clemson uses 3 to 6 inches, Texas A&M 4 to 6 inches and NC State 6 to 8 inches. Water them in once, then leave them alone. Texas A&M says no more water is needed until shoots appear, because the roots dislike disturbance. Mulch to hold moisture and buffer winter cold. If a freeze below about 25 to 28°F is forecast, cover the plants with frost cloth.

Planting in cold-winter areas (zones 3 to 7)

You have two options, and both aim for flowers before summer heat.

Plant outdoors directly. NC State Extension suggests planting corms several weeks before the last frost, once hard freezes are over. Clemson says to wait until the extreme hard-frost dates have passed. The dates for your zone above show the window.

Pre-sprout or pot up indoors for earlier, more reliable flowers:

• Alaska Master Gardeners soak the corms, set them in a tray of moist potting mix in a dark, cool spot at 40 to 50°F, and leave them 10 to 14 days until they have swollen and grown small white rootlets. They then plant them out on the safe date. Pre-sprouted plants flower about two weeks earlier than corms planted dry. One Anchorage planting bloomed 12 weeks after pre-sprouting began.
• Iowa State’s Reiman Gardens starts corms in pots about 12 weeks before the last frost: two or three corms 1 inch deep in a 6-inch pot, kept bright and cool, no more than 60°F by day and 45 to 50°F at night. The plants go outside just after the last frost.

The When to Plant Ranunculus page explains both schedules in more detail.

Site and soil

Choose full sun, at least 6 to 8 hours according to Clemson. Drainage is the deciding factor. NC State says ranunculus will not tolerate heavy clay and does best in sandy, well-drained soil. In wet ground the roots rot. On clay, plant in raised beds or containers.

In pots, use a free-draining mix and a container with drainage holes. Clemson says to choose a pot big enough for the full-grown plant.

Care while growing

Once shoots appear, keep the soil evenly moist but never soggy. Iowa State feeds potted and garden plants with a soluble fertilizer every two weeks while they grow. Deadhead spent flowers to keep new buds coming.

Ranunculus do best in cool spring weather. Solano County Master Gardeners note that bloom ends once days stay above about 70°F, so plan your planting date to put flowering in the cool part of the year.

Cutting for the vase

Ranunculus are excellent, long-lasting cut flowers if you cut them at the right stage. Cut when the buds show full color and feel soft and squishy, like a marshmallow, but have not opened. Cut the stem low, near its base, which encourages more blooms. Strip leaves that would sit below the waterline, recut the stems indoors and change the water every two to three days. Texas A&M reports stems lasting up to 10 days.

After flowering: keep or replace the corms

Let the foliage yellow and die back before removing it, because the plant is still feeding the corm. The plants go dormant in summer heat.

• Zones 8 to 10: corms can stay in the ground and may rebloom. Do not water dormant plantings, because wet summer soil rots the corms. Many gardeners, including Solano County Master Gardeners, still plant fresh corms each fall for a dependable display.
• Zones 3 to 7: dig the dormant corms, cut off the tops and store them in a cool, dry place until the next planting.

Common problems

• Root or corm rot: caused by heavy or poorly drained soil, overwatering dormant corms, or soaking longer than 4 hours. Plant in sandy soil or raised beds and limit the soak.
• Freeze injury: plants are damaged below about 28°F and corms die below about 25°F. Cover plants or delay planting.
• Flowering stops early: heat above about 70°F ends bloom. Plant early enough to flower in cool weather.
• Skin irritation: the sap can cause redness and blisters in sensitive people. Wear gloves when handling.