Here's how to grow ranunculus. Your growing zone and particular growing situation will dictate when your ranunculus should be planted. Zones 7 and higher or those with high tunnels can plant them out in fall. However, those in colder zones with no greenhouses should plant in very early spring. I am in 6b and do not have a high tunnel. I find that planting them out approx. 4-6 weeks before my last frost date and protecting them with a low tunnel made of wire hoops and frost cloth works best for me. Don't plant them outside until you are sure the ground won't freeze. Experience is the best teacher - especially when it comes to ranunculus. Everything that I'm sharing with you today is from trial and error on this particular land and in this zone. You will need to adapt to see what works best for you. You can find links to other grower's in other zones at the end of this tutorial.
In my zone corms should be planted out approximately 4-6 weeks before the last frost. Before planting I soak and presprout to give them a head start. This should be done 2 weeks before planting out.
When you purchase ranunculus corms they will be shipped to you in a dry dormant state. The corms can be stored dry and at room temperature for several months. No special treatments is necessary. Plan to start the soaking and presprouting process two weeks before you plan to plant them out in the garden.
Place the corms in a bucket of room temperature water and soak them for 4 hours. The water temperature should never exceed 55 degrees F. I place mine in old daffodil bags so they are easy to lift out of the bucket. Change the water every hour to avoid the build up of bacteria. You can also use a fish pump to arrate the water or leave a gentle stream of water running in the bucket for the 4 hours. I find simply dumping the water every hour works just fine.
Once the corms are soaked it is time to presprout them. Presprouting will result in blooms about 3 weeks earlier and will help us weed out any "dud" corms. Fill a planting tray that has no holes with lightly moisten high quality potting mix to the depth of about 1-2 inches. It is VERY important that the soil is not wet, just lightly moistened. Place the corms with the tuberous fingers pointing down in the medium. They can be placed very close together. We will not be growing them in this tray - just presprouting them. Cover the corms with a light layer of lightly moistened soil. Once again - not wet - just lightly moistened.
At this point some people will tell you to cover the tray with a dome. I personally found this problematic so I do not cover the tray at all - however, find what works best for you. Place the tray in area that stays dark and cool. The ideal temperature is 50 degrees. The soil should stay slightly moist during this time. Never wet, and not bone dry. Leave the tray in this cool dark area for approx. 2 weeks. Check them every day or so for any signs of rot and discard any corms that are moldy or rotten immediately.
Once about 2 weeks have passed you will see that the corms have developed roots and have begun to sprout. This is the right time to plant them out in the garden. Once again try to correlate your presprout with the time you want them to go out into the garden so that you are not trying to hold over corms that are ready to go outside.
Ranunculus need full sun and well draining soil. The plants can take cold ground and cold temperatures, but the corms should never be allowed to freeze. Before planting, incorporate a good 2-3 inches of compost to the bed. Plant the corms 2 inches deep and about 9 inches apart. I have head some growers push the spacing to 6 inches apart, however, I have never personally tried this.
Next I hoop and cover my plants with a frost cloth. I use Agribon 30 and metal hoops that are bent by a local farmer. I use metal staples to secure the cloth to the ground.
Ranunculus open in the day and close at night. Harvest Ranunculus after they have opened and closed a few times, generally 3 days. If the center bud feels hard, wait, and check it the next day. It should feel squishy like a marshmallow. Harvest in the early morning. You can cut them more open, they will just have a shorter vase life. You can expect a vase life of 10 days.
Once the weather warms up you will see the Ranunculs start to go dormant. Don't worry, this is normal. Ranunculus do not like long hot days and will stop producing when temperatures are consistently in the 70s.
Zone 6b/7a with high tunnel - lovenfreshflowers.com/2014/02...
Zone 3/4 - www.blossomingbough.com/blog/...
Zone 8-10 - www.localflowerco.com/blog/20...