Winter Ranunculus
Like anemones, we’ve grown ranunculus several different ways. Now, we grow them in the winter in very much the same way we grow the anemones.
We grow them in the winter because by the time they are safe to plant out in the spring, we are seeing such crazy temperature fluctuations that they typically go dormant pretty quickly without producing more than a couple stems per plant.
We also had mixed results in the locations we grew them in outside. We’d have a great year in one unheated tunnel, replicate our process the next year in a different tunnel and just get smacked with the worst case of powdery mildew. A damp or humid spring can make things tricky.
In that case we ended up stripping out all the plants and foliage, removing all landscape fabric and drip line from the tunnel and closing it up for a good “cook”. We solarized the tunnel over the course of a few hot days in the spring to kill off the powdery mildew before re-starting in that space with other crops. That worked for us. Temperatures of 90F and higher kill powdery mildew. For reference: on a 38F sunny winter day with a closed tunnel, we can achieve 99F!
Even indoors in the winter, ranunculus are not super producers for us. And they don’t pay enough rent to hold on to a lot of table space here. We’ll cut back next year even more and grow more bulb plants, I suspect.
Here is the video from the IG post. Scroll down for A LOT more info.
Growing in pots:
Anyhow for the ranunculus: We use 1 gallon pots and we fit about 7 pots per bulb crate. The bulb crates make it easier to move pots around. They also make it easier to water the plants. Ranunculus resent over watering. They need to dry our between waterings. They are Mediterranean. That’s the kind of climate you need to create for them. With the pots, we can thoughtfully water some plants and exclude others if they don’t need it. When we plant in crates, it’s all or nothing and generally we tend to do too much here.
Our ranunculus woke from dormancy planted in their pots (with a pretty bankrupt soil — mostly just soilless mix), outside set up off the ground on pallets that we line up in a long row. We pretty much ignore the anemone and ranunculus during the summer. The cooler temps and fall weather “wake” them up and they start to sprout. The cooler it gets, the more growth they put on. When we start to get consistent cold, freezing temps, we move the ranunculus in their pots into our heated tunnel.
Pre-sprouting with trays
For pre sprouting ranunculus we use 50-cell deep root trainers. We soak the ranunculus and then plant them with soil mix in these deep root cell trays. The trays keep all the roots organized so there is no untangling for planting. And they allow for a lot of root growth. With our short season, we like to get our plants going nice and strong before we put them out, since we have to wait longer than most people to plant into unheated structures or field rows.
Growing Temperature:
We keep our greenhouse at 50F in the winter for the most part, unless we have a crop in there that we are trying to hurry along. Then we might have the heat turned up to 60, but we really don’t go warmer than that. Ranunculus like 50F. That is our target temperature during both the growth and finishing phases.
Fertilizing
We feed the plants at a rate of 60 ppm nitrogen (about 1.5 grams of granular 15-5-15 fertilizer mixed into a 5 gallon bucket of water) during the growth phase and then can boost that feed to about 150 ppm nitrogen (about 3.5 grams of granular 15-5-15 fertilizer) during the flower finishing phase. We’re using the same fertilizer as described in the anemone post. We fertilize about once a week when we’re watering. Be careful not to over fertilize ranunculus. Over-fertilized plants can be extra susceptible to aphids. Aphids love nitrogen. And so do ranunculus. And thus our battle begins.
If you don’t know how to calculate the ppm for your granular, water soluble fertilizer, here is a resource to help you.
Pest Concerns:
We use both diatomaceous earth and neem oil fogging to help control the aphids. But it can still be REALLY hard. The buggers get under those umbrella shaped ranunculus leaves and they are kind of shielded from everything. Occasionally we evict a crate or certain pots all together if we think they pose a threat to other plants. A bad apple can spoil the bunch and aphids can spread to other crops. Unfortunately most beneficial insects require temperatures around 65-70F and warmer. They are just not effective around 50F for us here.
In a comparison of anemones, ranunculus, and butterfly ranunculus grow side-by-side, we do notice SUBSTANTIALLY fewer aphids on the butterfly ranunculus. They are the last to sport them - probably due to the fuzzy texture of their leaves. So, if you are fed up with anemone and ranunculus because of aphids (I don’t blame you), consider giving butterfly ranunculus a try.
WINTER BLOOM TIME:
Our ranunculus are coming on stronger and producing lots more flowers now that the days are getting longer. They really didn’t take off for us, though, until after Valentine’s Day. We probably could have added more light to make them come on stronger. They receive about 3 extra hours of supplemental light, but it is not really strong, direct light— just a bit of an extra boost.
Greenhouse numbers talk:
Our ranunculus plants will produce about 4 bunches of 10 stems per 3 sq. ft. this season (from when we brought them into the tunnel in October to when we evict them when they get too hot and go dormant next month). Maybe other people can get more stems out of that space with ranunculus. It’s about 5-6 stems per plant. And we have to really work for that.
In the same 3 sq. ft. for the same period of time we can instead grow:
40+ bunches (400 stems) of specialty tulips in successions.
or
150 potted hyacinth bulbs in successions.
or
350 paperwhite / daffodil bulbs in successions.
or
some foliage plants for winter mixed bouquets - like 2 mature foxtail ferns, or a nice big overwintered eucalyptus.
If I had to choose, I’d probably take any one of these options over the ranunculus any day. One of the things that makes bulb crops so profitable is that they don’t need a long growing phase. Many can enter your growing space and be flowering less than a month. Of course, there is a lot to learn/understand about bulb forcing to do this well, but the payoff can be substantial. This process doesn’t apply to an area in which you can’t control the climate. (like when growing outdoors during the spring) But even so, it’s important to consider your resources and time and the profitability of the space you give up to grow one plant over another.
What’s the purpose?
If you love ranunculus for their beauty and you have a good purpose for them for sale (I loved having them when I was doing a lot of wedding work— I could add a lot of value to them as a designer when I priced my products) then, by all means grow lots of ranunculus.
Growing Outside:
If you decide to grow them outdoors in the spring or fall (that’s an option, too!) I recommend purchasing some shade cloth to cover your growing area when it starts to get too warm and/or growing in crates or pots that you can move to full shade when it starts getting too warm. The availability of that shade cloth or the portability of your plants can help you extend your season if things heat up quickly.
HERE IS A SHORT LIST OF THINGS TO REMEMBER:
Ranunculus like 50F. Do what you can to achieve that temp. while they are growing and when they are flowering. Use frost cloth or move your plants to a shady place if possible when temperatures get too warm.
Ranunculus like to dry out between waterings and they like to dry out pretty quickly. Plant them in well-draining soil. If you are container growing, water each container as it requires.
Fertilize with about 60 ppm nitrogen during the growing phase and about 150 ppm nitrogen during the flowering phase. We do this about once a week with watering. Do not over-fertilize. If you need help to determine the rate of dilution for your own granular, water soluble fertilizer, use this tutorial.
Know your purpose for growing this flower. Take notes and determine how productive it is for you. Is it the right plant for you to grow? If you’re wavering, remember that you can make the most profit by selling your stems retail in design work. Beginner growers probably should not plan to grow ranunculus for wholesale buyers.
For more information about growing ranunculus check out the culture sheet from Syngenta in the downloads section.