Success with presprouting ranunculus
Gardeners know that starting seeds indoors can give you a head start over direct sowing in the garden. Instead of waiting for the snow to melt to put seeds in the ground, we scratch that itch to see green things with a little potting soil, trays and grow lights. It might not seem obvious, but flowers grown from corms can be started indoors as well. Before I was a flower farmer, my only experience with presprouting corms came from gladiolus. My short prairie summers meant that getting gladiolus flowers was next to impossible when planted just as a corm outdoors in May. Most of the older gardeners I knew started their corms indoors (often in an old ice cream pail!) then transplanted them into the garden when green leaves appeared and the risk of frost was minimal. Success with spring ranunculus in our climate follows a similar route, although for different reasons. Ranunculus are not damaged by cold weather like gladiolus are: in fact they love it. The key to getting beautiful ranunculus flowers in my Zone 3 garden is to get them growing as early as possible, before the season heats up. Ranunculus grow best when daytime temperatures are less than 17C and nighttime temps are just above freezing. This is a short window of time most years in Alberta as our spring can be very hot. Prolonged heat causes ranunculus to stop growing, turn yellow and die back. To avoid losing my plants and potential flowers to hot weather I start corms indoors a month before I expect to plant them in the ground. Here are the steps I take in presprouting:
Corms ready for a soak
1) My corms come from my wholesaler in nice mesh bags so I can soak several varieties at once without mixing colors. If you don’t have mesh bags, they can just be placed in a container and done one color at a time. I place my bags of corms in a large pail and place the pail in my bathtub. I fill the pail with cold water, making sure the corms are submerged.
2) I leave the corms to soak for 4 hours, with the water running with just enough pressure to create bubbles. This oxygenates the water and creates a healthier environment than still water, which can promote rot in your corms.
Those bubbles are what I want to see!
3) After four hours, I remove the bags of corms from the water and drain well. I transfer them to a different bucket for a quick soak in an organic fungicide while I prepare the trays. I use an organic fungicide called Actinovate which is not readily available to home gardeners. A natural anti-fungal alternative is 1/4 cup apple cider vinegar in a gallon of water. I soak for 15-20 minutes in Actinovate then remove.
Anti-fungal treatment to protect my corms.
4) I use 100% vermiculite as my sprouting medium. Over the years I have tried 100% potting mix, 50/50 potting mix and vermiculite and have settled on pure super fine vermiculite. I have had the best results and the least amount of rotted corms with this method. I wet the vermiculite so that it is damp but not dripping wet and fill my 1020 trays halfway full. Trays are labelled with each color and then corms are placed closely but not touching to avoid passing disease.
100 corms per tray
Plump corms ready to be covered
5) The corms are covered completely with more damp vermiculite and placed on racks to sprout at 10C. I check the moisture levels occasionally making sure the corms stay covered and the vermiculite doesn’t get too dry. The trays can be misted to maintain moisture levels but should not be watered. After two or three weeks, roots start to emerge followed by the stem shooting up from the crown. At this point, the corms can be planted if your ground is ready. If not, you can pot them up in large plug trays or 4”pots to continue to grow until the weather and your garden is ready for them. This whole process is exactly what I do with anemone corms as well. Anemones prefer the same cool conditions as ranunculus and I grow them together every year.
A chunky corm at the perfect planting stage
One last word about selecting ranunculus corms for your garden. I get asked quite often if I sell corms and the answer is no. I grow ranunculus bred by Biancheri in Italy and they strictly regulate the reselling of their corms. Besides that, they are an expensive way to learn to grow this beautiful flower. If you are new to growing ranunculus or haven’t experienced much success with it before, I suggest you do what I did when I started out: buy cheapo garden centre corms! My local Canadian Tire store stocks corms each spring, in small, inexpensive amounts. A bag or two of these is the perfect way to learn without breaking your bank account. The only thing worse than having a mouse or vole eat your precious ranunculus corms is having them eat your precious, EXPENSIVE ranunculus corms. Save yourself the heartache and expense!