Growing Ranunculus for Fall Blooms

Text and Image Heather Henson of Boreal Blooms @borealblooms

I had always thought it would be impossible to grow ranunculus here in Alberta. Unlike tulips or narcissus, the corms cannot freeze in the ground. Everything I read recommended fall or late winter planting and a long, cool growing period to get blooms in April and May. We very often have snow covered ground until May and winter temperatures always hit at least -30C, if not colder. No chance for fall planting here without a heated greenhouse, which I don't own. I wasn't ready to give up on my ranunculus dreams though, so in 2016 I bought a cheap mix of 100 corms and decided to just follow all the steps and put my presprouted corms in the ground as soon as I could work the soil. I soaked the corms starting April 1st and placed them in my heated garage to sprout,, which was a perfect 10C. I planted them out on April 20th, the night before I left for the Floret workshop (where I met Louise!). Despite some nights that still dipped below freezing, they grew well and bloomed six weeks later, around June 1st. I gave them no special treatment, didn't even fertilize them and I had a good crop of blooms, just in some awful colors. That mix was cheap for a reason!! By July 1st, they had slowed down significantly and started to brown up. I thought this meant they were diseased but after asking flower friends, I learned that this is how they signal they are going dormant as the conditions are not favorable for them anymore. I ripped them out a week later after there were no more buds on the plants, giving me a five week bloom period. Although I was happy with my initial trial, I wanted to see if more flowers were possible.

During the winter, I researched ideal growing conditions for ranunculus. I found that although my spring time temperatures were perfect for them, my day length was not. Ranunculus like cool nights, below 10C and day time highs less than 21C. Cold Lake perfectly fits that description in May and June, however by Summer Solstice we have almost 19 hours of daylight. Ideal conditions are 8 to 12 hours of sunlight or what is referred to as "short days". Flowering will still occur if they are grown under longer days, as I experienced, but there will be fewer flowers and some corms may not flower at all. The work around to this is to create short days with shade cloth or actual shade. The more I thought about this, the more I wondered why I shouldn't try growing them in September/October as well as May and June. Being at 54.5 N, the sun starts to get weak by the middle of August and our night time temperatures drop back below 10C. I decided to save some of my corms for a fall trial and compare the results with spring grown ones.

My plan was to get my first batch of corms in the ground by April 15th, so I soaked and put them in trays to sprout in my garage March 31st. Then a foot of snow fell on the Easter weekend and my plans went sideways. My corms sat for a month in flats and 50 cell trays, growing taller by the day. Finally the snow melted and I was able to plant them out on April 30th, two weeks later than planned. I planted half in my raised beds in full sun and covered them with 30% shade cloth. I used a mix of Agribon 19 and bug netting to create shade over the corms planted in full sun. The other half of my sprouted corms I planted in raised beds that were in the shade of my house and only received about 8 hours of daylight: four in the morning and four in the late afternoon evening. The full sun corms with 30% shade bloomed seven weeks after planting, about the third week of June. They flowered and burned out in three weeks. It was beautiful, but not ideal. The ones planted in part shade bloomed a week later and flowered for longer, about five weeks. It was interesting to note that the delay in planting created by the snowstorm exactly matched the shortened flowering interval. Two weeks later planting resulted in two weeks less flowering compared to 2016.

In the midst of all this I remembered I had to get my fall trial soaked and sprouting. Honestly that was tough to force myself to do, as I had just finished getting my summer garden planted and the last thing I wanted to do was soak and sprout more corms. For the sake I science, I sucked it up and got it done. I soaked and put the corms to sprout in my cooler at about 7C on July 1st. The spring planted/full sun ones were finishing up by mid July, so I ripped them out and flipped the beds, amending with compost and organic fertilizer. I planted corms on July 21st but did not put shade cloth on them as I knew the angle of the sun would soon mean it wouldn't be necessary. The other half of my spring planted corms I left in the ground to see if I could get a second flush of flowers from the new tubers they were producing underground.

Fall blooms started arriving the first week of September, seven weeks after planting, just like in spring. There were immediate differences in flower quality. I grew the same varieties in spring and fall, Viola, Bianco and Cioccolato Elegance series from Italian Ranunculus. The fall planted flowers were shorter by a couple of inches but with much thicker stems. The flower heads were bigger and there were more branched stems with multiple flower heads on the stems. The blooms came at a much more reasonable rate than in spring/summer when I felt like I couldn't keep up. One downside was thrips. The very first Violas to bloom all had thrips damage on their petals. Spring planted ones had none as the little beasts seem to arrive here about August 1st, just in time to ruin my dahlias. After the first flower was cut from each Viola, I didn't notice anymore damaged petals though so the cold nights must have slowed them down. A killing frost arrived this week, in mid October, ending my flowering period. I think if we had been free of a hard frost for a few more weeks, the plants would have continued to bloom as there were still lots of buds on the plants and they showed no signs of going dormant. I could have covered them with Agribon 19 but that would have blocked what little weak sunshine we are still getting so I don't think I would have gained anything. I also wanted to see how tough they were. The buds and plants are definitely hardy to at least -3C. Oh, and those corms I left for a second flush? They came up and are green and lush but no flower buds. I think they may have flowered had they been in a sunnier location but right now they get almost no direct sun. Always next year!

This is my experience in my unique climate, but I think fall blooms are possible in many other places in Canada and the USA. Check your local average temperatures to see when your days and nights would be cool enough to meet the ideal growing requirements, and plan your sprouting cycle around that. Allow two weeks for sprouting and at least 6 weeks for blooms. Besides enjoying the beautiful flowers for longer, succession planting means you don't have to panic when you order too many corms to fit your space. Plant half in spring and half in late summer, shopping problems solved!

If you have tried this, or plan to in 2018, please let Louise and I know how it turns out. We can all benefit from seeing how growers in different regions maximize their harvest of these beauties. Cheers to the end of your season and happy planning for 2018!