How To Grow Amazing Ranunculus
Ranunculus are hands-down, my favorite flower of all time. Every season we grow nearly 10,000 of them in our hoophouses, and I. Cannot. Get. Enough!! When I first started growing flowers, I tried to grow ranunculus in the field but they never performed well. The yields were low and the stems were short – but they are absolutely magical if grown with a little protection in a hoophouse. Our average stem length is between 2-4 feet, depending on the variety, and the blooms are massive.
When learning to grow a new cut flower, I always find it useful to consider their native environment. Ranunculus are native to the Mediterranean area and therefore like to grow over a long time in the cool winter, and then they become dormant during the dry summers. They begin to grow again in the fall when the rains come. The better you understand this and try to imitate this environment, they more success you will have.
Varieties & Sourcing
Ranunculus can be purchased as seed or corms, but are most commonly grown from corms. There are many different varieties of ranunculus grown for cut flower production, but the most popular are the:
· Labelle Series
· Amandine Series
· Romance Series
· Italian Elegance Series
· Cloni Ranunculus
Keep in mind that Butterfly Ranunculus have recently become very popular, however, they have different growing techniques and requirements than regular ranunculus.
Be careful not to purchase dwarf varieties, as the stem length will not be long enough for cut flower use. The Labelle and Amandine series are perhaps the best to trial for beginning farmers, as they are affordable and fairly easy to grow. The Italian type ranunculus (elegance and Cloni) are much more expensive. The Cloni series are also tissue-cultured and patented, so it is illegal to save and re-plant the corms. New ones much be purchased from the supplier each year OR a royalty fee must be paid. This is important to note because the breeders who have spent a lot of time, effort and money to develop these varieties deserve to be paid for their hard work.
In my experience, most of the amandine and labelle ranunculus flowers are much smaller than the Italian varieties, however, the colors are absolutely stunning. The amandine and labelle series also tend to have more “singles” develop, rather than the big, fully petaled and fluffy looking double flowered type. The Italian varieties hardly ever seem to vary from the traditional double-flower type. The singles resemble poppies, however, and they can add a lot of variety and texture to bouquets (especially fun for wedding work!). One last difference is the labelle series seem to bloom earlier, while the amandine series bloom a bit later and are more tolerant to heat.
For commercial growers, the labelle and amandine series can be purchased through Ball Seed, the Italian varieties through Onings. Be sure to place your orders the spring before you need them (order early!!).
Growing Requirements
Ranunculus require a well drained soil and an ideal pH of 5.8-6.3, although our pH is around 7 and they grow beautifully. As with most flowers, the beds should be kept weed-free. They do NOT like heat, and should be grown with ideal nighttime temps around 40* and daytime temps between 50-60*F. That being said, I have found that Ranunculus are VERY hardy, and can handle extremely cold temperatures with a little extra protection. If soil temps exceed 70*F the plants will begin to shut down, stop producing, and go dormant.
When to plant
Ranunculus do best when planted in the fall in zones 6 and above (maybe even 5 and above). If you are in zone 5 or below, they will most likely do best planted in early spring. Timing varies with your microclimate, but I find the best results with fall planted ranunculus in a hoophouse. I don’t recommend growing ranunculus in the field – in most places they will need some minor protection to grow quality blooms. Our first succession gets planted into the hoophouse early to mid November. We do three total succession plantings, each planted about a month apart. One thing I’ve noticed: the later in the season the successions, the shorter the stem length will be.
Soaking Ranunculus Corms
When you receive your ranunculus corms, they will be shriveled and resemble brown, dried banana clusters. To start ranunculus plants, they need a fair bit of water to get started. You can simply pop the corms into the ground and water the heck out of them to accomplish this, but I prefer to soak and pre-sprout them in the greenhouse first then transplant them. I find this produces much more uniform results.
To soak your corms, place them in a mesh bag (most of them arrive in mesh “onion bags”) and plop the bag in a bucket of room temperature water. Many people aerate the water using aerating stones (like those found in a fish tank- which can be purchased at any pet store). We used to do this, but then started soaking our corms without it bothering and have found absolutely no difference.
For most varieties, we only soak the corms for 2 hours (a maximum of 3 hours). Any longer than that and I’ve found the corms start losing their little legs! You DON’T want this! You want the corms to stay intact as much as possible so they have lots of energy to grow big, tall, and strong flowers.
Pre-Sprouting Ranunculus
Once they’ve soaked in the water for a couple of hours, take the bag out of the water. Your corms should look plump and firm instead of shriveled at this point. You can soak in a fungicide (such as rootshield or actinovate) for 10-15 minutes to minimize rot issues. Like with the aeration stones, we started skipping this step with no rotting issues, but it’s not a bad idea to do.
From here, there are many different methods to pre-sprout. You could simply plant them in the ground, or grow them on in the greenhouse for a few weeks. We always grow on in the greenhouse to ensure more uniform growth.
To pre-sprout, we use regular pro-mix or perlite. You can use peatmoss or another growing medium – they aren’t too fussy. We slightly dampen the growing medium and plant in either 50-cell trays or in 1020 flats. I’ve found it much faster and easier to plant in the 1020 flats, but it is nice to grow out a root ball with the 50 cell trays if you don’t have many to transplant. If using a 50-cell tray, fill the cells halfway with soil, plant the corm, then cover with soil. If planting in a 1020 tray, put a layer of soil on the bottom of the tray, then plant corms in a single layer, and cover with more soil. You can choose to “layer” your plantings here to save space and materials, but I have found that doing this leads to much less uniform rooting. All trays are placed in our greenhouse on a heat mat set to between 55-65*F. Within 7-10 days or so, most varieties have developed lots of healthy white roots and are ready for transplanting into the hoophouse!
SIDE NOTE – I have heard of other farmers pre-sprouting right in the mesh bags the corms arrive in by simply adding soil to and around the bag, but I have never tried it. For me personally, this seems too risky for rot.
Transplanting
When transplanting, we plant at a 5” grid spacing, about ½”-1” deep. Most suppliers recommend a more generous spacing of 6-9”, but we’ve found better results and taller stems with planting closer. Experiment on your own farm to see what’s best! Make sure to water in well (we overhead water right after transplanting). We don’t use landscape fabric or plastic mulch- they do best planted in bare ground that is weed-free.
Growing On
While growing ranunculus, try to keep temperatures as even as possible – although if you live anywhere in the Northeast like I do, you know that’s basically impossible. If temps dip below 28*-30*F, we cover with one layer of frost cloth (we use spring hoops to keep the frost cloth low but off the tops of the plants). If temps dip below 22*F, I add a second layer of frost cloth. We have never had a crop killed – even in -16*F nights we have only had very minor frost damage on plants right near the doors (where there was a major hole that we have now patched).
A couple of major keys to keeping ranunculus happy:
· Use drip irrigation and keep leaves as try as possible
· Water sparingly during winter – especially if your hoophouse is humid. We water MAYBE once a month, depending on weather and conditions. Over-watering will lead to rot and disease.
· Ventilate, ventilate, ventilate!! Get as much airflow in the tunnel as possible.
· Keep everything well weeded (a wire weeder or tine weeder will be your best pal)
· Keep an eye out for botrytis, leaf spot, and mildew. Ranunculus can be prone to powdery mildew, which is why ventilation and airflow are so important. If you have limited air flow and no fans in your hoophouse, a few bio-fungicide applications (like cease) can help a lot.
· Keep an eye out for pests, especially APHIDS. Be sure to scout every other day or so for these awful little insects. Their population can explode overnight and ruin your entire crop (speaking from experience here). Ranunculus are also prone to leaf miners, spider mites, thrips, and whiteflies.
· We only fertilize our ranunculus maybe once or twice in late winter/early spring, and don’t find it necessary to fertilize more often.
As far as netting goes, we don’t use it. We get super long stems but they don’t flop over, so we don’t waste our time with it.
Harvest & Post-Harvest
Finally, your ranunculus will begin to bloom in springtime! They are a STUNNING sight to see. We usually get our first blooms in mid-late April here in NY. Remember that while ranunculus foliage will hold up to ultra-cold temps, buds and flowers will not, so you must protect them appropriately from late freezes.
Ranunculus can be harvested in a few different stages. Harvest in soft bud/marshmallow stage if you are going to store them (in the cooler, duh), for any length of time. Keep in mind that the flowers will be smaller if you harvest them in this stage. If you wait a few days until the flower opens up and closes a few times, the flower will be much bigger in size (& take up more space in a sleeve, & be worth more money…). We harvest when the flowers are mostly open, and still get at least 10+ days of vase life out of them.
Harvest early in the morning and immediately place in cold water. We don’t find a need for any preservative, but if we are going to hold them for more than a day or two, we use a holding solution.
It’s imperative to keep the soil as cool as possible to get the longest harvest window from your ranunculus. We use shade cloth on our hoophouses and regular irrigation to accomplish this. Be sure to put the shade cloth on early in the spring, BEFORE it gets hot.
Digging & Storing Corms
Once temperatures rise, the ranunculus plants will automatically begin to shut down. You’ll have to remove the corms, or else many of them will come back in late fall, when you likely will have something else planted there! You can save your corms to be planted for next season (if they are not patented varieties like Cloni), or you can dig and just buy new ones for the following season.
I’ve experimented with leaving them in the ground and treating them like perennials, but with disappointing results. The plants do not grow back very uniformly and the bed gets fairly patchy from some dying (although I suspect this may be due to losing many from rot because they were planted in an outside bed that was super wet). Most grow back, but it’s more important to me to have a full bed of uniformly blooming plants than a patchy one.
To dig (and save) corms, simply wait until the ranunculus plants have mostly turned brown and are dormant. I stop watering once the plants start to shut down to speed up this process (it also makes pulling them easier). Then simply grab them by the base of the stem and pull straight up! If your soil is friable, they should come right up. If your soil is hard, use a broadfork to loosen the soil prior to pulling. Snip off the foliage/any stems left on, shake off any excess soil, and toss into a bag or crate. You can wash the soil off the corms, or if you are lazy like I am, just keep it on.
Store used corms in a dry, fairly warm (but not hot) environment until it’s time to replant. I find that I still get really good germination with used corms (about 95%), but get even better with corms fresh from the suppliers (99.9%-100%).
Happy growing!!