1. Depending on where you live and what kind of setup you’re working with, you can plant your ranunculus corms in either autumn or late winter/early spring, in a place where they’ll get full sun. In areas with mild winter temperatures (USDA zone 7 and above), corms can be planted in the autumn and successfully overwintered outdoors with the protection of a low tunnel or frost cloth. In colder areas (USDA zone 6b and below), ranunculus must be grown in a minimally heated hoop house or held back and planted out at the end of winter or in early spring. If corms are exposed to temperatures below 25°F (−4°C), they will freeze and ultimately rot once they thaw, so be sure to protect them from extreme cold.
2. When you unpack your corms, you’ll notice they resemble little brown octopuses and are probably not what you were expecting. Don’t worry—these strange little critters will produce an abundance of striking blooms come spring.
3. Before planting, soak corms for 3 to 4 hours in room-temperature water. It’s important that you don’t oversoak them—they will rot. As the corms soak, they will plump up, often doubling in size. After soaking, corms can either be planted directly into the ground or presprouted. Presprouting the corms before planting will mean flowers bloom a few weeks earlier.
4. To presprout, fill a flat-bottom seed tray half full of moist potting soil. Sprinkle the soaked corms onto the soil, and then completely cover them with more soil. Leave the tray in a cool place (40°F–50°F / 4°C–10°C) for 10 to 14 days in an area where rodents can’t find it. Check on the corms every few days, making sure the soil is moist but not soggy, and remove any corms that show signs of mold or rot.
5. During this time, corms will swell to about twice their original size and develop little white rootlets that resemble hair. Once rootlets appear, it’s time to plant them in the ground. Before planting, it’s important to prepare the growing beds. We add a generous dose of compost (2 to 3 in / 5 to 8 cm) and a balanced organic fertilizer (such as Nature’s Intent 7-2-4) and mix it thoroughly into the soil. Ranunculus corms are planted 9 in (23 cm) apart at a depth of 2 to 3 in (5 to 8 cm), with 4 rows per bed. Plant corms with the “octopus tentacles” pointing down.
6. During cold stretches, when temperatures dip below freezing, cover the plants with a layer of frost cloth. Autumn-planted corms bloom in early spring, and late-winter or early-spring-planted corms will flower by midspring.
7. We always get lots of questions about how to store ranunculus corms until it’s time to plant them and about whether they can be left in the ground to rebloom the following year. Corms can be stored in the bags they arrive in; keep them in a cool, dry place until it’s time to plant. In colder climates, grow ranunculus just like annuals and plant new corms each season. If you’re a gardener in USDA zone 7 or above, you can leave your corms in the ground and they may bloom the following year depending on multiple factors, such as how cold your winter is, how well your soil drains, and how much pest pressure you have in your garden. I never count on overwintered corms and plant new ones every year. If the overwintered ones return, I always count it as a bonus.
8. Ranunculus have an outstanding vase life, often exceeding 10 days. Cut when buds are colored and squishy like a marshmallow, but not yet fully open, for a vase life of 10 to 12 days. If the blooms are open when cut, they’ll still last a week but will be more fragile to transport. Be sure to cut spent flowers down to the base to promote new blooms.
With their ruffled, rose-like blooms in shades of pink, red, yellow, white and purple, ranunculus flowers are showstoppers in any garden. While ranunculus thrive outdoors in mild climates, you can get a head start on these beauties by starting them indoors. In this comprehensive guide, we’ll cover everything you need to know about when and how to sow ranunculus seeds or plant ranunculus corms indoors for healthy transplants.
Native to the Mediterranean region, ranunculus prefer cool conditions and do best in zones 8-10 where winters are mild They can be grown as annuals in zones 4-7 given proper care Established plants tolerate light frosts but prolonged freezes will kill them. This delicate flower thrives in well-draining, slightly alkaline soil amended with compost to improve drainage. Ranunculus also require at least 6 hours of direct sun daily, with some shelter from hot afternoon sun to prevent scorching.
When grown indoors and transplanted at the right time, ranunculus reward gardeners with an abundance of breathtaking blooms earlier than sowing directly outdoors. Timing is critical to get the most out of these beauties.
When to Start Ranunculus Seeds or Corms Indoors
Starting ranunculus indoors gives you a jump on the season compared to direct sowing outdoors. The timing depends on your target transplant date based on your local last spring frost date. Count backwards from your desired transplant date:
- 8-10 weeks for ranunculus grown from seed in individual pots
- 12-14 weeks for ranunculus grown from seed direct sown in flats
- 10-12 weeks for ranunculus grown from corms
Here are some general guidelines for indoor sowing and planting dates
- January to February: For transplanting seedlings or corms outdoors in March/April
- March: For transplanting in May
- July: For growing as fall annuals and transplanting in September/October
Stagger sowings and plantings every 2-3 weeks for a longer flowering window.
Step-by-Step Guide to Starting Ranunculus from Seeds Indoors
Follow these steps for success with sowing ranunculus from seed indoors:
- Use fresh seeds within 1-2 years of harvest and opt for an 80%+ germination rate
- Sow seeds in sterile seed starting mix in containers, gently firming the mix and watering before planting
- Plant seeds on the surface without covering since they need light to germinate
- Water lightly with a spray bottle to keep surface moist but not saturated
- Provide bottom heat at 60-65°F for optimal germination
- Give bright light with grow lights close to emerging seedlings
- Transplant carefully when second set of true leaves appear, handling delicate stems with care
- Harden off young plants slowly over 7-10 days before transplanting outside
Step-by-Step Guide to Starting Pre-Sprouted Ranunculus Corms
Follow these steps for planting pre-sprouted ranunculus corms indoors:
- Soak corms in room temperature water for 3-4 hours until doubled in size
- Pre-sprout corms by planting 1 inch deep in trays of moist soil. Store in cool dark spot for 10-14 days.
- Plant sprouted corms in pots with well-draining potting mix, 2 inches deep and 6 inches apart
- Grow indoors under lights, watering when soil surface is dry to the touch
- Harden off for 7-10 days prior to transplanting outside after danger of frost
- Plant outdoors in well-draining soil in full sun, providing frost protection if needed
Success Tips for Growing Ranunculus Indoors
Here are some top tips to help ensure success with growing ranunculus indoors:
- Select the largest corms available for best blooms and vigor
- Discard any soft or moldy corms which may rot
- Use sterile potting mix and clean containers to prevent disease
- Allow soil to dry between waterings to prevent root rot
- Give plenty of light from grow lights or a sunny window
- Maintain cool indoor temperatures around 60-65°F
- Gradually harden off plants before transplanting outdoors
- Time transplanting carefully based on your local last spring frost date
- Protect from frost and wind for 10-14 days after transplanting outside
With the right sowing or planting time, careful handling, and optimum growing conditions, you’ll have sturdy ranunculus starters ready to transfer to the garden for an eye-catching display. Properly timed, your indoor-raised ranunculus will reward you with a bounty of breathtaking blooms earlier than spring planting outdoors.
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What You Will Need
- Top-quality ranunculus corms
- Potting soil or peat moss
- Compost
- Organic fertilizer
- Frost cloth
- Drip irrigation or soaker hoses
- Depending on where you live and what kind of setup you’re working with, you can plant your ranunculus corms in either autumn or late winter/early spring, in a place where they’ll get full sun. In areas with mild winter temperatures (USDA zone 7 and above), corms can be planted in the autumn and successfully overwintered outdoors with the protection of a low tunnel or frost cloth. In colder areas (USDA zone 6b and below), ranunculus must be grown in a minimally heated hoop house or held back and planted out at the end of winter or in early spring. If corms are exposed to temperatures below 25°F (−4°C), they will freeze and ultimately rot once they thaw, so be sure to protect them from extreme cold.
- When you unpack your corms, you’ll notice they resemble little brown octopuses and are probably not what you were expecting. Don’t worry—these strange little critters will produce an abundance of striking blooms come spring.
- Before planting, soak corms for 3 to 4 hours in room-temperature water. It’s important that you don’t oversoak them—they will rot. As the corms soak, they will plump up, often doubling in size. After soaking, corms can either be planted directly into the ground or presprouted. Presprouting the corms before planting will mean flowers bloom a few weeks earlier.
- To presprout, fill a flat-bottom seed tray half full of moist potting soil. Sprinkle the soaked corms onto the soil, and then completely cover them with more soil. Leave the tray in a cool place (40°F–50°F / 4°C–10°C) for 10 to 14 days in an area where rodents can’t find it. Check on the corms every few days, making sure the soil is moist but not soggy, and remove any corms that show signs of mold or rot.
- During this time, corms will swell to about twice their original size and develop little white rootlets that resemble hair. Once rootlets appear, it’s time to plant them in the ground. Before planting, it’s important to prepare the growing beds. We add a generous dose of compost (2 to 3 in / 5 to 8 cm) and a balanced organic fertilizer (such as Nature’s Intent 7-2-4) and mix it thoroughly into the soil. Ranunculus corms are planted 9 in (23 cm) apart at a depth of 2 to 3 in (5 to 8 cm), with 4 rows per bed. Plant corms with the “octopus tentacles” pointing down.
- During cold stretches, when temperatures dip below freezing, cover the plants with a layer of frost cloth. Autumn-planted corms bloom in early spring, and late-winter or early-spring-planted corms will flower by midspring.
- We always get lots of questions about how to store ranunculus corms until it’s time to plant them and about whether they can be left in the ground to rebloom the following year. Corms can be stored in the bags they arrive in; keep them in a cool, dry place until it’s time to plant. In colder climates, grow ranunculus just like annuals and plant new corms each season. If you’re a gardener in USDA zone 7 or above, you can leave your corms in the ground and they may bloom the following year depending on multiple factors, such as how cold your winter is, how well your soil drains, and how much pest pressure you have in your garden. I never count on overwintered corms and plant new ones every year. If the overwintered ones return, I always count it as a bonus.
- Ranunculus have an outstanding vase life, often exceeding 10 days. Cut when buds are colored and squishy like a marshmallow, but not yet fully open, for a vase life of 10 to 12 days. If the blooms are open when cut, they’ll still last a week but will be more fragile to transport. Be sure to cut spent flowers down to the base to promote new blooms.
How I Grow Ranunculus (+ Schedule of Planting Dates)! // Garden Answer
FAQ
When should I pre-sprout my ranunculus?
No special treatment is necessary. Two weeks before you are ready to plant them outdoors, you should soak and pre-sprout the corms.
What month is best to plant ranunculus?
Planting of both anemones and ranunculus ideally takes place in the first half of October but can happen as late as mid-November for abundant spring blooms in our region. We soak and pre-sprout the corms per the directions sent by Gloeckner with the order.
How cold is too cold for ranunculus?
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Freezing Temperatures:Ranunculus corms are susceptible to freezing, and temperatures below 25°F (or -4°C) can cause them to freeze and rot.
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Frost Tolerance:While ranunculus plants and flower buds can endure freezing temperatures, prolonged freezing is not recommended.
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Protection:During cold snaps, it’s advisable to protect ranunculus plants with frost cloth or other coverings to prevent damage from freezing temperatures.
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Hardiness Zones:Ranunculus are hardy in USDA plant hardiness zones 8 to 10, where temperatures typically don’t plunge below 25 degrees.
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Corm Planting:Plant corms with the “octopus tentacles” pointing down.
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Soil Conditions:Ranunculus thrive in well-drained soil, so avoid soggy conditions that can lead to corm and root rot.
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Air Circulation:Maintain good air circulation around the plants to prevent powdery mildew, a common fungal disease.
Do ranunculus come back every year?
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Perennial in Warm Climates:In zones 8-10, ranunculus are considered perennials, meaning they can survive the winter and bloom again the following year if the corms (underground stems) are left in the ground.
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Annual in Colder Climates:In colder regions (zones 4-7), ranunculus are typically treated as annuals, meaning they are planted each spring and the corms are not likely to survive the winter.
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Corm Storage:If you live in a colder climate and want to try to overwinter ranunculus, you can dig up the corms in the fall, store them in a cool, dry place, and replant them in the spring.
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Planting Time:In warmer zones, ranunculus can be planted in the fall for spring blooms, while in colder zones, they are typically planted in late winter or early spring.
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Growing Conditions:Ranunculus prefer cool, moist conditions and well-drained soil. They also need full sun to partial shade.