by Megan O’Mullane
I fell in love with ranunculus in the spring of 2020 when I was working for Greta Lewanski on her cut-flower farm, Turnstone Farm, in our Airport Heights neighborhood. The ranunculus was blooming ahead of everything else because she had started them so early. They had the same lush, romantic appeal as peonies but were blooming in a far wider range of colors, and I knew I had to try growing them for myself. Last year was my first season growing ranunculus in my own garden and although they took some work, it was worth the reward to see their happy blooms in June.
Ranunculus is a large genus consisting of around 600 species including several Alaskan native wildflowers such as snow buttercup and Lapland buttercup. The variety we are familiar with as an ornamental plant or cut flower is Ranunculus asiaticus, also known as ‘Persian Butter-cup’. They are a tuberous-rooted plant with semi-double to fully double blossoms with multiple layers of pa-per-thin, silky petals.
Ranunculus asiaticus is native to the Eastern Mediterranean, Southwest Asia, and Southwest Europe, and is only winter hardy in growing Zones 8-11. If ranunculus plants or corms are exposed to temperatures below 25 degrees Fahrenheit, the plant will die, or the corm will freeze and then rot once thawed. In Alaska, ranunculus is an annual, and we need to treat it like a dahlia or anemone by planting the corms in the spring for summer blooms.
Ranunculus grow from corms which look like little octopus. The size of the corm indicates the number of flowers that will bloom, so if you have a choice, choose the biggest corms you can get. The best time to purchase corms is the fall because online stores typically sell them then, when folks in warmer zones are planting them directly outdoors with other bulbs such as tulips and daffodils. If you buy corms in the fall, you can store the corms over the winter and start them whenever you like in the spring. If you wait until spring to purchase corms you may have to wait until May for delivery because vendors may not be willing to ship them until the risk of freezing during shipping has passed.
To figure out what is the earliest date you should start your ranunculus in the spring. I suggest asking yourself when you can ensure your corms and plants will not be exposed to temperatures below 25 degrees Fahrenheit. In my garden I use low tunnels over raised beds to get an early start on the season. I also have frost cloth (i.e., Remay garden cloth) that I can blanket over plants during the early season to buffer against cold frosts. This year, I plan to pre-sprout my corms indoors around mid-April, and plant them out into my raised low tunnels at the end of April. If you live in Anchorage and you don’t have any raised beds or protection against frosts, a safe bet for a planting-out date is mid-May. The Alaska Garden Helper is an easy way to determine expected last spring frost.
Once you figure out a safe date to plant out ranunculus for your growing area, you can either wait for that date and plant the corms directly into the garden, or you can pre-sprout the corms indoors two weeks before that date. Pre-sprouting will allow the plants to flower around two weeks earlier than they would with planting directly. Either way you will first need to soak your corms for 3-4 hours in room temperature water. I leave the tap running slightly for the duration to aerate the water. Do not soak the corms longer than 4 hours because this may cause rot.
To pre-sprout the corms you will need a space that is dry, dark, and minimally heated (between 40-50 degrees F). If you don’t have a space like this then I suggest plant the corms directly into the garden. If you have the right environment for pre-sprouting (often a basement, workshop space or arctic entry), you can go ahead and fill a flat-bottom seed tray half full of moist potting soil. Then place your pre-soaked corms onto the soil about 1” apart and finally cover them completely with more moist soil. Leave the corms for 10-14 days. During this time check on the corms every few days to make sure the soil is moist but not soggy and remove any rotting corms. During this time the corms swell to about twice their original size and develop little white rootlets that resemble hair. At this point they are ready to plant in the ground.
If you would like to cut your ranunculus blooms to enjoy them inside, to maximize vase life they should be cut when buds are colored and squishy like a marshmallow but not yet fully open. If you cut the stem down at its base it will promote new blooms, and after all that honest hard work growing them, you deserve as many blooms as you can get.
This article was previously published in the March 2022 Alaska Master Gardener Newsletter .
About Heidi Rader