Ranunculus is an invaluable cut flower for floricultural production due to it's long vase life and stunning rose shaped form. Growing it requires attention to quite a few factors, making it a tricky crop to learn at first. But the effort is worth the profit margin, so stick with it and reap the benefits :)
In Dallas, Texas we have heavy clay soil which often stays wet throughout the winter. Ranunculus are grown from corms that easily rot in wet situations. Additionally, Ranunculus prefer cool temperatures but are not very cold hardy. For these reasons, a successful crop depends on a protected growing environment. We grow our Ranunculus in our unheated high tunnel. We mound up our rows by 3 inches to provide adequate drainage in deluge rain situations and use a propane heater in extreme cold scenarios (sustained temperatures below 28F).
Our Ranunculus is autumn planted to give it the needed 90 days of cool weather to reach maturity before blooming. Once Ranunculus experiences consistent daytime temperatures above 80F and nighttime temperatures above 60F, dormancy is triggered. Those temperatures arrive for us here in April. By planting in November, we can usually have Ranunculus blooming the entire month of March.
Occasionally, our Autumn weather is cool enough to plant Ranunculus in October. However, warm spells in January trigger blooming right before the onset of extreme cold in February. The extreme cold damages the blooms which often leads to a delay in secondary flushes, missing the ideal March conditions. For this reason, we do not attempt to schedule an early ranunculus harvest. Our sales are most robust in March as the spring wedding season begins and we protect that harvest by delaying Autumn planting until November.
As an urban, micro farm, we can not leave any space unproductive, so we presprout our corms and plant only those with strong healthy roots. We soak our corms in aerated water for roughly 1.5 hrs then place them in moist (not wet) promix and put them in our flower cooler for 2 wks, checking them every 3 days to be sure they aren't drying out. We set our cooler to 55F in October because the outside temperature is usually warmer than this and we don't have a basement. We use the same cooled space to concurrently grow our cool flower seedlings under lights. The ranunculus corms aren't placed under lights, but they do get some residual light. This doesn't seem to affect their sprouting.
Originally, we grew a mix of Amadine and LaBella varieties. We noticed that Amadine held up better in heat but rotted much quicker in wet years. By contrast, LaBella doesn't rot as much but is affected by heat. We now grow mostly half-clone varieties for our regular Ranunculus production as it seems to endure both conditions with less issues. We added Butterfly Ranunculus to our production and, despite the high cost of corms, were surprised to find it the most profitable Ranunculus variety in our lineup. This is due to very little pest or disease issues, extreme productivity even through heat, and a higher price point in our sales channels. Our regular ranunculus can struggle with aphids, thrips, botrytis and stem topple while the butterflies remain unfazed.
Our clay soil is naturally high in nitrogen and because we grow in a tunnel and irrigate with city water, the salt content is also pretty high. (Pro-tip, check your water PH and not just your soil). Both of these things can inhibit calcium uptake, which leads to stem topple. We spray KNF on our ranunculus to combat this. We also don't add any fertilizers. I once made the mistake of fertilizing and we had so much extra nitrogen that the aphids had a feeding frenzy that spring. For the last several years, I put up blue sticky traps for the thrips and released ladybugs to deal with aphids. Thrip pressure is usually low here but aphids come on pretty strong. Thanks to a recent presentation by the ASCFG, I recognized that my thrip traps were also trapping phidoletes aphidimyza, which look like little delicate black flies - a beneficial insect that eats aphids much more successfully than ladybugs. I immediately put away the thrip traps and the aphid pressure disappeared in two days! It's possible that I've been shooting myself in the foot these past several years with thrip traps; I've had much more aphid pressure while using them.
Botrytris is a disease of mold due to wet cool conditions. Some years we have a very dry winter and don't deal with this at all. Other years, our winter clay never dries out and we battle this constantly. Spacing is always a tricky thing: too little and botrytis can take out a crop if the year is wet; too far and we lose out on valuable production space. This spring (2024), I'm not growing either anemones or poppies on production scale and I'm glad: both are very prone to botrytis and it's one of the wetness years I've ever farmed in. The ranunculus are struggling with botrytis and I've spent hours every day hand-clearing rotting leaves from the understory and making sure there's no leftover leaves rotting anywhere. If my farm was larger, this approach wouldn't be feasible, but there's some bonuses to only having a micro-farm. We haven't experienced any crop loss yet, but I do regret a tighter spacing that I decided on (9 inches) for my butterflies and 6 inches for my half-clones. Next year, it will be back to 12 inch and 9 inch spacing respectively. Field crops such as delphinium and foxglove are also struggling with botrytis, made more pronounced by the layer of leaves our shade trees left behind in Autumn.
I don't net my ranunculus. The stems have never been tall enough to warrant support and with proper nutrients, the stems are sturdy and straight. Our high tunnel has a 30% shade cloth on it year-round, helping to mitigate our early spring warmth and causing the stems to stretch and lengthen. In Texas, our sun is strong enough to provide the necessary light intensity in the winter for good flowering.
The first several years of production, I followed some commonly held advice to cut the flowers while they were pretty tight in bud. This is a good approach if you're dealing with pest issues and you want the flower to open in the protected space of a cooler than a field of pests, or if you're field growing and you don't want rain to damage the flower. However, the flowers don't tend to open as fully or reach the full potential of their size. I now wait until the buds are open a bit. They last just as long in the vase but tend to be a bigger size and open more fully for my florists. In short, they command a higher price point. I'm of the opinion that most people are harvesting their ranunculus far too early. Like any cut flower, proper harvest is accomplished by sharp, clean snips and a sanitized bucket with clean fresh water. Strip the leaves and store at 36F in low humidity (or you could have mold spores show up on the flowers while in storage).
Some excellent resources for ranunculus cut flower production can be found in the member section of the ASCFG website. The 2024 National Conference in St. Louis had a presentation on growing ranunculus and a recent "Ask the Experts" video deals with common pests of ranunculus. THIS is also an excellent production guide you can download from the Utah State University Extension office. To make your own calcium spray (KNF or LAB), here's a great video tutorial by Bare Mtn Farm.
Happy Growing!
Sarah Jo