This ranunculus planting guide will show you how to pre-sprout, plant, grow, and harvest beautiful ranunculus flowers. Gardeners in zones 7 and higher, and gardeners in zone 6 with a high tunnel can plant ranunculus corms in the fall. However, gardeners in zone 6 and lower, who don’t have a high tunnel, should plant ranunculus in very early spring for the best results.
Ranunculus are tender corms that will arrive from the supplier in a dry, dormant state. The first step is to soak and presprout them. Start this process 6 weeks before the last frost. It will take 2 weeks to presprout the corms inside, and presprouted corms should be planted into the garden 4 weeks before the last frost.
Begin the pre-sprouting process by soaking the corms in a bucket of room temperature water for 4 hours. Do NOT allow the water temperature to exceed 55 degrees F. Change the water every hour by dumping out the old water and refilling with fresh water. You can also use a fish pump to aerate the water or leave a gentle stream of water running in the bucket. After four hours, the corms will have plumped up and doubled in size.
Next, fill a watertight flat bottom tray with 1-2" of lightly moistened, high quality potting soil. It’s important that the soil is moist but not sopping wet. The corms are literally swollen with water after soaking and planting them in a “just-moist” medium encourages them to root out in search of water.
Place the soaked corms into the soil with the tuberous fingers pointing down. You can space them close together because they’ll only be in the tray for two weeks. Cover the corms with about an inch of lightly moistened potting soil so they’re completely covered. Place the tray in a cool, dark area with an ideal temperature of 50-55 degrees F.
While the corms are sprouting, the soil should stay slightly moist. Never wet, and not bone dry. Check the corms often and immediately discard any that are rotten or moldy. If you notice that your corms are molding or rotting the medium is likely too wet or the location is too humid. If you notice the medium is getting too dry add a bit of moisture.
After about two weeks, the corms will have sprouted and developed roots. This is when they should be planted out into the garden.
Plant ranunculus in full sun and rich, well-draining soil. Prepare the planting area by incorporating several inches of compost into the soil. Plant the corms 2” deep and 9” apart. If there’s a chance of freezing temperatures, cover the planting area with hoops and frost cloth. Keep the bed weed free as the ranunculus grow and fertilize with fish emulsion as needed.
Ranunculus prefer cool nights at 45-55 degrees F, and sunny days at 60-70 degrees F. They’ll begin flowering about 90 days after planting, and pre-sprouted corms will flower approximately 3 weeks earlier than dormant corms planted directly into the garden.
Ranunculus make wonderful cut flowers. For the longest vase life, harvest ranunculus at the base of the stem when the flower is half open. The bud should be colored and the center should feel squishy like a marshmallow. Flowers harvested at this stage will have a vase life of 1-2 weeks.
