Updated: Oct 18, 2022
Ahh, ranunculus. These gorgeous blooms stole my heart in 2020. Chris and I had purchased around 300 or so, a mix of pinks and whites. Looking back, we had no idea what we were getting ourselves into! We have created this guide to help you be successful in growing these must-have flowers.
So you want to grow ranunculus...
If you're like me, you probably saw a picture of a ranunculus somewhere, gasped, and said, "Omg I have to have it". Little did I know that these things are the divas of spring. They don't like it hot, but they don't like it too cold. They like water, but only at the right time. And they want to be fed. Always.
What you will learn in this post
When growing ranunculus, I feel like I need to be Mary Poppins with a carpet bag
They prefer to have ALL the things. They like a nice aerated compost tea bath to soak in before you ask them to sprout. They need a blankie outside for when the temperatures drop. They want nutritious meals served to them at least once a week. They want it all. And they want it now.
That being said, you can successfully put your ranunculus on a minimalist diet of a tap water presoak and allow your soil to feed them. The one thing they will need if you are growing in a colder climate is winter protection.
To protect ranunculus you will need:
frost cloth or light sheets
weights to keep the cloth from blowing away
some sort of low hoop to raise the sheet off of the plants as they grow
Ranunculus need blankets for cold weather. When ranunculus are young and small, you can simply float the sheet over the top of them and anchor it down to keep it from blowing away. As they grow, you can make low wire hoops, maybe a 18" or so off the ground to float the cloth. We used a thick wire meant for fencing to hold our cloth up (we got ours at Fleet Farm), stuck into the ground on both sides of our beds.
Although typically not necessary for short crops like ranunculus, you can also create larger tunnels to be able to work in by getting and bending conduit like shown above. We prefer these for taller crops.
The photo above is from a night where we were worried the temp would hit 26*. Yes, you heard that right.
I remember having massive amounts of anxiety about ranunculus being damaged by anything under 40*. Despite their diva attitudes, these babies are TOUGH. Lots of lost sleep and covering, uncovering, and covering again taught us that ranunculus only need protection if you are concerned that the temps will hit 26*. In our area, we check the forecast and cover if the weather channel says 28*. Oftentimes our microclimate is a touch colder than what is predicted in town.
That being said, all plants should be hardened off properly before exposed to temperatures like this. I don't like going from a 75* basement into the 30* weather, and plants don't either.
When to Start Your Corms
If after reading the above paragraph, you are guessing that ranunculus need to be started early, then you would be right. In SE Wisconsin, we start our corms in early February, babying them along inside until our temps warm enough to get them out into the ground.
A key note about ranunculus is they stop producing when the ground temperatures hit 70 degrees. This means that if they had their druthers, they would prefer 65* sunny days and 40-50* nights. They thrive in a long, cool spring. This means getting them outside as soon as you can and allowing them to relish in the cool conditions.
Ranunculus bloom between 12-16 weeks after planting. Ranunculus should be started and presoaked indoors around 12 weeks before your last frost date. A quick Google search of your zip code and 'last frost date' should let you know when yours is. Then count back 12 weeks from there.
How to Presoak Your Corms
"What does 'presoak' even mean?!"
If you have seen ranunculus corms, then you know that they look like small, dried octopi. Presoaking is the process of giving your little octopi a nice long drink of either water or compost tea to get them ready for their growing adventure. If you don't have compost tea or don't want to make it, plain tap water works just fine, too.
At Dogwood, we presoak our corms in a bath of compost tea (don't worry, I will make a blog post on compost tea too) for about 3 or 4 hours, or until they are plump. We also use an aerator to keep any bacteria from becoming anaerobic during the soak. This step isn't necessary but is recommended. We use a simple fish tank air pump and stone.
No, this picture is not great, but it does show the difference between a dry corm and a presoaked corm. The corm on the left is dry, shriveled and sad looking. The one on the right looks juicy, plump and ready to pre-sprout.
Wait - pre-sprout?
Yes, you read that right. Pre-sprouting is the process of testing corms to ensure viability. If you are a home gardener, this step is not necessary.
Pre-sprouting is generally used by flower farmers who are growing large quantities of ranunculus. Pre-sprouting benefits:
allows you to identify bad corms by seeing which ones don't sprout
pre-sprouting takes up much less space than growing on, preventing any bad corms from taking up valuable bed or growing shelf space
easy to get them 'started' without going through all the work of potting them up into cells, blocks or crates if you are short on time (though they do eventually need to be potted up about 10 days later)
After presoaking, corms are put in moist potting medium (or vermiculite or even perlite), and left in a cool, dark spot to wait for roots to develop. You can pre-sprout ranunculus by starting them either in cell trays or flats. Any way you choose to do this, you want to ensure that the corms are humid but not wet - corms will rot if too moist during this step.
Once you see roots developing (usually after about 10 days or so), you can bump them into larger containers.
Growing Ranunculus On
Once you have presoaked (and possibly pre-sprouted), you are ready to put those plump corms into potting medium. They can be started in cell trays (we ideally recommend larger ones such as 38-50 cell to accommodate larger corms), crates, or flats. They can also go directly into the ground if you aren't worried about freezing temps where you live. We have used all three methods (except the in-ground method). We have even used large soil blocks in crates with a lot of success.
Grow your ranunculus on until they have a solid set of small green leaves. Once the weather warms to the point where you aren't worried about freezing daytime temps, you can plant them outside, being mindful to cover them when temps reach 26-28*. For us, this is usually the beginning of April.
We plant ours about 4-6" apart for flower-farming purposes, but the home gardener does not need to plant them that closely. Anywhere from 6-12" apart can work for the garden, depending on your preference. I think planting in pods of three in a 6" triangle would be my garden preference.
Once you have planted your ranunculus outside, it will just be weeks of agonizing over the weather and running in and out of your house to cover and uncover them as the temperatures fluctuate. Easy peasy! In all seriousness though, these gorgeous blooms are totally worth it.