How To Grow Ranunculus

With their endless ruffled layers, long vase life, wide color range, and robust blooming habit, it’s no wonder ranunculus are a spring favorite amongst growers and floral enthusiasts alike. Even though they are known for being strong producers, they grow from tender corms and will need extra protection from the cold temperatures during your winter months. When carefully tended to, they will produce an abundance of blooms in your garden when spring time arrives.

Depending on where you live, what your growing zone is, and what resources you have available, you can plant your ranunculus corms in either autumn or late winter/early spring. If you do not know your USDA hardiness zone, you can look it up here.

If you live in an area with mild winter temperatures (USDA zone 7 or higher), your ranunculus corms can be planted in the early months of autumn and successfully overwintered outdoors by using the protection of a low tunnel, frost cloth or other form of insulation depending on your location. If you live in areas where your temperatures dip much lower (USDA zone 6b or lower), you will likely need to grow your ranunculus in a hoop house or other growing structure, or they can be stored and planted out at the end of winter or in early spring.

As with anything, every growing situation and location is unique to itself. I know other growers that have successfully overwintered their ranunculus in zones lower than 7 by using multiple layers of frost cloth and growing under low tunnels and mulching heavily. Just keep in mind that if corms are exposed to temperatures below 25°F, they will likely freeze and ultimately rot once they thaw, so make sure you have a plan to protect them from extreme temperature swings. Like with all growing, it may take a few seasons to explore and discover what works best for you.

How To Pre-Soak Ranunculus

Your corms will arrive in a dry and dormant state, many say they resemble tiny brown octopuses. Even though they may not look special, they hold so much potential and beauty inside. You can keep your corms in the package they arrived in and store then in a cool, dark place away from critters until you are ready to soak them.

When you are ready to pre-soak, unpack your corms from their package and set them aside. Next, you will gather a container and fill it with room temperature water. Place your dry corms in the water, soaking them for 3-4 hours. If you are growing a lot of corms, you can use a fish tank bubbler or keep the faucet lightly dripping over the container, to help aerate the water. Do not leave your corms in the water any longer than four hours, as over-soaking them can lead to rot. Because I grow so many, I like to put mine in a mesh bag for ease of removal out of the water.

As the corms continue to soak, they will swell and plump up, often doubling or tripling in size. When your soaking time has finished, you can choose to either plant your corms directly into the ground or choose to pre-spout them. If you choose to pre-sprout the corms before planting, it will allow you to sort through and see which corms will grow successfully so that you do not waste any garden space. It will also push their growing cycle up by a few weeks, giving you blooms up to two weeks earlier.

How To Pre-Sprout Ranunculus

When pre-sprouting your corms, fill a container or flat bottom seed tray half full of moist potting soil. Make sure that the soil is lightly moist, not drenched, as your corms are sensitive to wet conditions, especially during this stage. I prefer to stay away from soil mediums that say “moisture control” and go with an option that has perlite to keep the soil light and aerated.

Take your pre-soaked corms and gently place them “feet down” on top of the soil in your tray. Then, sprinkle enough lightly moist soil on top of the corms so that they are fully covered. Again, make sure your soil is lightly moist only, not too damp. Place your tray in a cool place for 10 to 14 days in an area where air circulates but there isn’t much, or any, light, or any chance for pests to find them. Check on the corms every few days, making sure the soil is still moist but not too damp, and remove any corms that show signs of mold or rot, as they will be unusable.

Once your corms start to sprout “tiny white hairs” you will know they are beginning to grow roots, and it is officially time to plant them outside. Some may even be sprouting tiny green foliage and ready to be in the ground.

Planting Your Ranunculus

Before planting, be sure to amend and prepare your growing beds. I like to add around 2-3 inches of organic compost that I purchase from my local composting company. I also sprinkle in a balanced fertilizer, thoroughly mixing it into the soil so that the ranunculus are consistently fed throughout the season. Ranunculus corms can be planted at 8-9 inches apart, at a depth of around 2-3 inches, in rows of 4-5, depending on how large your beds are. Like we did in pre-sprouting, be sure to plant your ranunculus corms “feet down.”

You do not want to plant your corms when it is too warm out. I always try to plant when I know it won’t rain for at least a few days, preferably a week, when soil temperatures are in the 60s. You can find your current soil temperature by entering your zip code on this site: https://www.greencastonline.com/tools/soil-temperature

Because I pre-sprout my corms, I like to do one deep watering after planting my corms just so the roots make good soil contact. If you pre-soak only, I would still make sure there is some initial moisture in the soil when planting, as you won’t want to plant in too dry of soil. I won’t water again until I see green sprouting and I have checked the moisture levels by placing my finger into the soil, as you don’t want to oversaturate your garden beds.

Ranunculus do not enjoy having wet feet, or frozen feet. During cold spells, when your temps dip below freezing, be sure to cover your ranunculus plants with a layer or two of frost cloth. You can also mulch around them for extra protection, depending on your climate and winter forecasts. Frost cloth comes in different weights, so be sure to purchase a weight appropriate for your weather. Plants perform best when the frost cloth is not touching the foliage - find something to prop up the frost cloth off the leaves by using garden stakes or small hoops that can be made out of wire hangers or other bendable medium found at your local hardware store. If needed in colder zones, you can also create low tunnels with rebar, 10ft PVC pipe and UV resistant 4 year greenhouse plastic in a width and length that you need - always go longer and wider than your beds and hoops to account for the need to tie off and secure the ends and weigh down the sides. There are plenty of videos online that can be found to create and use this method. If you experience an arctic blast and you notice the foliage becomes damage - do not fear, if the corm did not freeze the foliage will grow back with time. The most important goal is to keep the corm from freezing. When temperatures fluctuate through the winter time, be sure to vent and/or lift your frost cloth to allow the plants to breathe, as you won’t want them to overheat. There will likely be times where you will find yourself lifting the frost cloth off for the day, then securing it again for freezing times at night.

When temperatures start to rise again in the 70s, a 30-50% shade cloth will help lengthen your stem length and the lifecycle of your ranunculus, giving you more weeks of production before your ranunculus go dormant for the season. As mentioned before, plants do not appreciate any cloth touching their foliage, so be sure to create some kind of hoop system or create a way to lift the shade cloth out of reach from touching your plants.

Harvesting Your Ranunculus

Ranunculus have an outstanding vase life, and are considered a “cut and come again” flower, meaning the more you cut from them, the more they continue to bloom in your garden. For the longest vase life, cut when the buds have started to color up and are not fully open just yet - at this stage, you will be able to gently squeeze them and they will feel soft like a marshmallow. Open blooms are not too far gone and can still be enjoyed, you can cut them and expect a vase life of usually up to a week, sometimes more. Be sure to cut with sanitized snips and immediately place them in fresh water after cutting. Continue to monitor the water quality in your vase and change it as needed to ensure maximum vase life.

The effort you put into caring for your ranunculus will reward you with an abundance of blooms. They truly are as prolific as they are beautiful and deserve a devoted space in every spring garden.

Wishing you a colorful, joyful and successful harvest!