Ranunculus Growing Guide
Share
Ranunculus Growing Guide
Once you're aware that ranunculus exist, you can't imagine a more perfect flower. Or at least that's what I felt when I first saw some. When I later discovered that I too could grow these beauties, the skies parted and the world was suddenly filled with unicorns and rainbows! "I can grow these myself?? Yes, please!! Sign me up!"
Of course, soon the phrase "no pain, no gain" became all too real. I fumbled along for a couple of years until finally, on my third year trying, I had more blooms than I knew what to do with. Luckily, this was a short lived problem because my customers, who also thought they were amazing, quickly bee-lined it to my store to buy them up.
The difficulty with growing ranunculus is not that we don't know what they want, we do... but to grow them in a way that allows them to reach their full potential requires usually some trial and error to determine what modifications we need to make to our growing environment so they can thrive.
In addition, whether we intend to grow them just for our personal enjoyment or as a flower crop, will also determine what makes most sense as well.
General Growing Info
Ranunculus are usually grown from corms that can be planted beginning in the Fall to very early Spring. They grow best in cool growing conditions (45 - 60 degrees F) which is what determines when we want to plant them in our gardens. They can’t tolerate very cold temperatures, if the corms freeze they will rot and turn to mush. But once it gets consistently above 70 - 75 degrees they start to shut down and go dormant.
To achieve this delicate balance of not too hot and not too cold, planting time is critical. The best timing for your area will require a bit of trial and error. Most likely you will need to provide some winter protection in the form of frost cloth and/or clear greenhouse plastic. If you have very cold winters, it might be necessary to wait until early Spring.
This is why they are called the “Divas of Spring” (they’re actually not called that- I call them that, but they should).
The general process for growing ranunculus is:
1) Soak corms in water for 3 - 4 hours
2) Plant directly in a prepared bed (if temperatures allow- this is usually in the fall) OR pre-sprout in a 1020 tray or 72 cell tray with potting mix that is barely damp and cover lightly.
3) If pre-sprouting: put in a cool spot and wait for a week to 10 days for roots to develop. Don’t let the potting soil dry out too much but it should not be too wet either. (LOL - see why I gave them the nickname).
4) Plant corms about 1 - 2 inches deep and about 5 to 6 inches apart in plant bed.
5) Protect from excessive cold or heat for about 90 days or so until they start to flower and make it all worth it.
Those are the basic steps to growing ranunculus from corms but sometimes the details are what matter so here are some thoughts expanding on the steps outlined above.
1) Soaking corms: Sometimes growers mention adding a fish tank bubbler to keep the water moving and to add oxygen to avoid bacteria buildup. I haven't found that necessary at the scale I grow. I used to change the water every hour or so but now I just either add more water halfway through the soaking period or change it once. I'm not even sure if this is necessary. Regarding how long you soak them: this can be variety dependent (butterfly ranunculus need more time) and possibly by size as well. The objective is to leave them in water long enough so they can plump up and kickstart the whole sprouting process. I have also forgotten (!) to remove the corms from soaking and left them overnight (approx. 12 hours total) and they were totally fine. It's important to not let them dry out after soaking so plant them right away.
2) Presprouting: I have always presprouted into 1020 trays and waited until they had roots and green sprouts before planting in the final bed. I like that I can control moisture and temperature much easier in my cool basement than if I planted directly in my unheated plastic tunnel outside. Of course, by doing this I'm adding a step that will affect costs by increasing labor and material inputs. However, at my scale, I prefer to lower the risk of losing my corms, despite the added step/expense. The KEY to pre sprouting successfully is to keep the correct moisture level of the potting mix. If too wet, then they are more likely to rot. If too dry, they might not sprout (or it will be delayed). I shoot for barely damp to the touch. You want to keep the corms that you just soaked, plumped and hydrated. This is a part that can be a bit of trial and error. However, I feel that as long as you aren't at one extreme or the other (soaking wet or bone dry) there is some leeway to figure out the best moisture for your growing environment and they will still grow. I like to partially cover with either a humidity dome or another 1020 tray. This helps keep the potting mix moist without drying out too quickly. I will mist or spray water every few days as needed. I use ProMix BX as a potting mix but other light (probably peat based) mixes will work. After arranging them in my 1020 tray I cover lightly with more slightly damp potting mix (the objective is to keep the corm from drying out). I keep them in the dark (not 100% sure this is even necessary) in my 60 degree F basement. After about 10 days I usually see little white roots and then a few days later, some shoots. Then I move them under some basic LED shop lights until I plant them out. Continue to keep them hydrated as they develop and grow. Recently, I've seem some growers pre sprout them in the fridge/cooler in mesh bags without soil but I have no personal experience with this.
3) Planting: This is probably the simplest part :) I plant about 5 - 6 inches apart. Cover the top of the corm with about 1 to 2 inches of soil. If you're in a colder climate I would plant closer to 2" deep as that extra soil cover will offer some protection from freezing temperatures. I don't use any type of Hortinova netting as I find they support the flowers upright without any issues.
4) Protecting: When growing ranunculus it's probably a good idea to have on hand frost cloth (I use Agribon Ag-19 and will double or triple the layers if necessary), 6 mil greenhouse plastic and shade cloth. These might all be necessary at one point or another. The extent of extra effort you'll need to put in to grow them will absolutely depend on your climate. If you have mostly mild winters with spring weather that heats up quickly, then Fall planting is the way to go most likely. If you have winters with many days below freezing then you will need to offer extra protection, probably in the way of low or high tunnels made with greenhouse plastic AND frost cloth. However, if it's sunny, these structures can heat up very quickly and can cook your plants if not vented. It might then make more sense to wait until very early spring (February) to plant them. What makes most sense for you will depend on your goals. The longer plants are able to grow and bloom in cool weather, the more productive they will be, but it might come at a high cost of labor if you need to baby them all winter. This is once again a process of trial and error to find out what works best for you, your growing conditions and your growing goals. The main goal is to not let the corms freeze (if only the leaves freeze they can resprout) and to have flowers before temperatures get consistently too hot (upper 70s and 80s) and the plant goes dormant. In April I add a 30% shade cloth over my tunnel as we start to have warm temperatures and usually by the 3rd week of May the ranunculus are going dormant.
Example: Last year I did 2 successions of ranunculus. One was pre sprouted in mid November and transplanted to their bed in my unheated caterpillar tunnel at the end of December (they were very overgrown but they handled it just fine). There was one very cold snap of 3-4 days with lows below 0 degrees and highs in the single digits in January but otherwise temperatures mostly hovered around mid 30s in January and mid 40s in February with the occasional cold spell. For the most part I only covered with frost cloth when it'd get below 26 degrees as the tunnel offers some protection. For that very cold snap I mulched with straw and used frost cloth and created a low plastic tunnel inside my taller caterpillar tunnel. I don't know if all of this was necessary but it worked and I didn't lose any plants. This succession started to flower at the beginning of April and were in full swing by April 10th.
The second succession was pre sprouted January 7th and transplanted at the beginning of February and they started to flower at the end of April. The first succession produced more blooms than the second BUT they were flowering at the same time as the tulips and so that created a bit of a problem as I was so busy harvesting tulips that I would fall behind on harvesting the ranunculus. I also then had way more flowers than I needed at the time. This year I'm going to delay the pre sprouting a bit so there is less overlap with the tulips and also so I can have the majority of my flowers ready for Mother's Day. I won't know if this is the best decision until I try it, which is the theme for ranunculus and flower growing in general if you ask me.
Pests: The main pest issues I've had are aphids and thrips. With aphids you need to be hypervigilant as their population will explode if you take a wait and see approach. Spraying is not very effective as they can get in between the petals of the flowers and the spray won't reach them. I prefer using beneficial insects such as green lacewings but they aren't able to undo a widespread problem if brought in too late. I've resorted to squishing them by hand (I know, gross, but somewhat effective) if I see them on a stem. You can also pull the plant and discard. Thrips is still a work in progress for me but I've started to use beneficial nematodes and hopefully that will be enough to keep them in check. I usually don't have too many problems with thrips until later in the spring.
Fertilization: From what I've heard, ranunculus are heavy feeders, which makes sense since they will pump out quite a few blooms in a short period of time. It seems calcium is important to helping with strong stems so adding something that will provide that is helpful. I like to use Espoma brand fertilizers when I need to supplement my beds.
Harvest: There are different views on the appropriate stage of harvest. One school of thought says to harvest at marshmallow stage (before the flower opens but the bud is soft and squishy). Others say to let the flower open and close a couple of times (they open with daylight and close at night) before cutting to get the biggest flower and longest vase life. I personally have seen how both situations can be correct. Early in the season when temperatures are still pretty cool, I have cut flowers that had been open for a while and brought them home thinking they were too old to sell (although they still looked great) and they had an amazing vase life and looked fantastic for a long time. Later on in the season when the days were warmer, I noticed flowers would blow open in the field much faster and therefore I started to cut them at an earlier stage (just past marshmallow).
Miscellaneous: Saving corms: This can be done. I did it my first year but it was quite a bit of work cleaning and processing them to save. You need to wait until the leaves die down and then you can pull the plants with the corms attached. Cut off the leafy material, remove dirt (I washed them my first year but I don't know if that's a good idea) and store in a paper bag in a cool spot inside. I'm think I'm going to try again this year.
That pretty much sums up everything I know regarding growing ranunculus. I'm sure I'll learn more this year too.
Best of luck with your growing endeavors and I hope you have a wonderful ranunculus season!
Andrea