Greater Philadelphia’s climate is far from ideal for growing ranunculus, but it’s possible to grow these popular cut flowers, even with our “blink and you miss it” spring.

In order to grow successfully, ranunculus need a period of about 3-4 months (that’s about how long they take to go from corm to bloom) where temperatures stay between about 25-70 degrees Fahrenheit. The cool, wet spring season of the Pacific Northwest is ideal for them - but here in the mid-Atlantic, we typically go from from chilly winters to sweltering summers too quickly for their liking. As a result, their environment needs to be manipulated a bit in order to increase the likelihood of a productive harvest.

Note: The below suggestions are also recommended for anemone, although anemone have a slightly lower preferred temperature range. They are best to start a couple weeks prior to ranunculus and will bloom a few weeks ahead of schedule, too. They cannot easily tolerate temperatures above 70-75.

Pre-Sprouting

One of the most important things is ensuring that the corms (that’s what their “bulbs” are called - they look like shriveled up miniature octupuses!) are properly pre-sprouted. This process helps gardeners get a jumpstart on growing them by encouraging good root development, which ultimately yields flowers a few weeks earlier. To pre-sprout them, first soak the corms in room temperature water for about three hours and, ideally, leave the faucet to drip slowly over them to keep them oxygenated. During this time, they’ll plump up quite a bit.

Next, take a large bin or deep tray filled halfway to the top with slightly damp soil, and place each of the ranunculus about an inch apart. Fill the top of the tray with the soil to ensure that each of the corms are fully covered. Leave them in a cool, dark area (an unfinished basement is ideal) and check every few days to ensure the soil hasn’t entirely dried out. If it has, water it lightly - but be sure to not let the soil ever get sopping wet, as it will cause the corms to rot. After 5-7 days (it depends on a number of factors and could take up to two weeks), you’ll begin to notice tiny little white sprouts developing on the “legs” of your corms. Once they’re an inch or two long, you’re ready to take them out of the tray and plant them!

When and Where to Start Them

The million dollar question! And before going too deep into this, it’s important to note that here in Greater Philadelphia, some years are pretty decent for growing ranunculus while some years are really rough. Ultimately, there’s no perfect answer for when and how to grow these cool-weather loving flowers - and there’s no way to predict what kind of weather the late winter and spring months will have in store for us.

If you happen to have access to a greenhouse or a hoophouse, this will be the best bet for keeping ranunculus happy and in their preferred temperature range. For the 99% of home gardeners who aren’t quite so lucky to have these growing structures at their disposal, there are still some decent options, which is what we’ll outline here.

As a general rule of thumb in our area, it is probably best to start pre-sprouting ranunculus in late January or early February with the plan of getting them outdoors in late February or very early March. That said, it’s not at all uncommon for March to see temperatures below 20 degrees at night, and your beloved seedlings will then need to get covered with hoops and a frost blanket. If growing them entirely outdoors in this way, you can pick up a few simple garden hoops (available online and at most garden centers - small/low ones are fine here) and a mid-weight frost blanket or Agribon fabric. The seedlings should be covered anytime the temperatures are expected to go below 20 degrees, and be sure that the plants don’t touch the cover itself. The fabric can be weighted down with cinderblocks, bricks, or garden staples to keep the cold air out.

Another alternative is to start them in a cool garage or basement, and transfer them outside in early spring. This may be the easier solution for most home gardeners, especially if you have room in your garage, and don’t care to construct low tunnels for them outdoors. The corms can be pre-sprouted in January or early February and then started in large cell trays (ideally at least 3”x3”) around mid February and placed under a quality grow light. Garage temperatures in our region tend to be pretty ideal for growing these flowers, and they’ll be ready to transfer outside to the garden in late March or so.

One important thing to note, though, is that they absolutely must be properly hardened off before transplanting to the garden; “hardening off” here refers to the process of gradually and intentionally getting the young plant acclimated to being outdoors and dealing with wind, rain, etc. Over the course of about a week, bring your trays of plant babies outside and let them sit outside - first for an hour or two, and then eventually working up to spending an overnight out in the elements. Of course, avoid doing this during any intense weather those first few days! After a few days, they’ll be ready to transplant to the garden.

The Details

Ranunculus thrive in rich, fertilized soil that is regularly watered. When planting your ranunculus in the ground (or in cell trays, if starting them that way), it’s recommended to add some rich compost or an organic fertilizer meant specifically for flowers. I typically grow them in an area where I mixed in our own compost a couple months earlier, and add a fish fertilizer two or three times throughout the spring.

When planting the corms directly in the garden or in cell trays, plant them with the sprouted“legs” facing down and cover them with about 2” of soil. They’ll get spaced about 8-10” apart in the sunny garden and will need frequent watering.

The first blooms will typically appear about three months after being planted (May is the big month for ranunculus in our region) and will peter out once temperatures regularly hit 80 degrees during the daytime.

Growing Cool-Weather Ranunculus