Ranunculus is a cannot-miss spring flower. They have incredible vase life, resemble a peony or a rose with their countless petals, and can bloom throughout spring.
While ranunculus take a bit more prep and fuss work than some other spring flowers (such as peonies, tulips or daffodils) when they bloom, they are spectacular.
And unlike tulips, daffodils and peonies, you can expect multiple flushes of blooms from ranunculus.
Last year was my first year growing them and I had some successes and failures.
Despite the failures, I'm hooked.
Here's how I grow ranunculus:
When to plant: In Seattle, you can plant ranunculus anytime in late October to early February.
It’s important to know that ranunculus benefit from cold stratification, meaning they grow better if they experience several weeks of cool weather before its time to bloom.
In general, the earlier you plant them, the earlier they bloom.
Ranunculus can survive temps down to 25 degrees for short periods of time. Fortunately, Seattle winters very rarely get that cold (and when they do, it's brief.)
I use frost cloth and leaves/mulch for a little extra warmth. (You don’t need frost cloth or mulch unless it gets below freezing for days at a time, but I like prepping it ahead of time.)
If ranunculus corms and plants are exposed to too much cold weather for too long; however, the corms will freeze and subsequently rot.
I started presprouting ranunculus the week of Thanksgiving, and have been starting a new batch every other week since then. I intend to presprout a new tray every week through January in hopes of having multiple waves of blooms this spring.
(Is presprouting ranunculus corms necessary? More on that in a minute.)
What you need to know about the corms:
When you buy corms, you are essentially purchasing what can be described as a dehydrated root (I think they look like calamari) that needs to be soaked (to plump up) before planted.
If possible, I recommend purchasing the largest possible sized corm. (Bigger = more blooms and typically more resistant to rot.)
There are many different varieties of ranunculus you can purchase that come in different shapes and colors.
Typically (not always though) the more expensive corms mean they are larger, produce more blooms, and are more rot and disease resistant. (But this does not mean you need to purchase the most expensive ranunculus to be successful -- cheaper varieties grow great as well.)
Soaking (recommended):
Once you have your corms, soak the octopus-looking things in room temperature water for 3 to 4 hours. (Don’t over soak, they’ll rot.) This hydrates the corms and helps them germinate faster and more reliably.
(I always soak them and set a timer for three hours, knowing full well I am likely to lollygag or get distracted before I actually get to pulling them out of the water and putting them in dirt.)
There are people on the Internet who claim you need to change out the water every hour, or you need to keep the water flowing (like with a sous vide or an aquarium pump) as you soak them. I absolutely do NOT do that.
I don't see the point of doing either of those things, plus my husband could kill me if I used our Sous Vide to aerate the water. (He instituted a strict policy of no-kitchen-items-shall-be-co-mingled-with-anything-gardening-related with me due to past incidents.)
Presprouting (recommended, but not required):
To presprout, I fill a flat-bottom seed tray (though any other container -- like plastic fruit packaging or a reusable take out-tray works as well) with moist potting soil. (Usually a half an inch or an inch of potting soil is enough.)
Sometimes the potting soil comes out of the bag moist and I just put the corms right into it. If it seems a bit dry, I will use a spray bottle to moisten the dirt.
Place the ranunculus corms on the soil (tentacles down,) then completely cover them with more soil (an inch or two of soil is usually sufficient.) Leave them in a cool place (40 to 50 degrees) for about two weeks (sometimes up to three weeks.)
If placing them outside (as Seattle winters are typically in the 40 degree range) I recommend putting a cover over them so the critters can't steal them. (Don't seal the container as this will likely decrease airflow and encourage rot.)
Check on them at least once a week to ensure the soil stays slightly moist (but not wet!) and none of the corms are rotting. (I've murdered enough ranunculus with too-wet of potting soil to know that the corms prefer slightly moist, not damp, soil.)
When the corms sprout white roots after two-ish weeks, they are ready for planting.
As to the controversial, much debated question, of do you really need to presprout?
And the answer is no. But I am an anxious ranunculus grower and I always presprout because I am wary of rot because our winters are so wet. HOWEVER, plenty of other growers in our climate don’t bother.
I personally have had a better result by presprouting; however, I do intend on experimenting again with not presprouting this year as well so I can better answer that question next year.
If you don't opt to presprout, then plant your corms immediately after soaking them for a few hours.
Tips for planting:
- Plant them with the tentacles down.
- Plant them 6-to-9 inches apart (I always plant 6 inches apart) and 2-to-3 inches under the surface.
- Add compost and a well balanced fertilizer when planting. (I top off my growing area area with an inch or two of Cedar Grow compost from Burien Bark, and mix in a well balanced fertilizer when I plant.)
End of season ranunculus care:
Ranunculus corms will go dormant when the weather gets too hot, which usually happens in Seattle in June-ish.
If you want to dig them up and store them to replant for the next season, wait for the foliage to naturally die back. Then dig them up, dry them and store them in a dark and cool area until you are ready to replant.
In the Seattle area, you may be able to overwinter them in the ground (and never dig them up) however corms are very susceptible to rot, so be sure to turn off any irrigation. (Full disclosure: I've never attempted this before.)
Saving corms for the following year:
You can treat ranunculus corms as annuals (that’s what I do); however, there is a way to save the corms for the following year. (I haven’t tried this before, but I’ve heard other people have success with it.)