Ranunculus – Growing in Cold Climates

Beautiful Ranunculus or Persian Buttercups come in a variety of both bright and subdued colours that will provide multiple blooms per corm. These plants flourish in the cooler temperatures of Spring and Fall weather and in many warmer places can be treated as a perennial. Growing them here in our Cold Climate however we either need to treat them as annuals and purchase new corms every year or we can take a few extra steps in the Fall to overwinter the corms indoors. Growing them here in the North is quite simple and our cooler temperatures will actually give you the opportunity to get blooms from them from Spring right through to Fall by simply staggering your starting times and planting locations.

In growing zones lower than USDA Growing Zone 7 Ranunculus corms should not be left in the ground over the winter. Here in the Kapuskasing Region we are considered to be USDA Growing Zone 2b, so a few extra steps are required to ensure beautiful blooms.

These are the corms we will have available in Fall 2021 and Spring 2022. We plan to have even more in coming years including the Picotee varieties!

When to Start

Ranunculus will take approximately 1- 1/2 months to start blooming from planting out, growth will slow in hot weather.

For Late Spring – Early Summer Blooms

Start corms indoors in Late Winter using the below instructions and direct sow or transplant pre-sprouted plants outside once risk of deep freezing has passed – approximately 1 month before last frost date for your hardiness zone. Be prepared to provide temporary protection in the event of unexpected cold/snow in Early Spring.
Zones between 6 and 4 should start February – March
Zones lower than 4 should start March -April

For Late Summer – Mid Fall Blooms

To get blooms for Mid August through the Fall follow the same instructions but start plants in Mid June through Mid July. Extremely hot weather will slow the plants growth so be sure to select your planting location for your Fall plants where they will receive midday shade in the hottest part of the Summer without being in Full Shade by Fall, alternatively grow in 8-10″ pots or large containers that can be moved to provide shade in the hottest part of summer and moved to a Full Sun in Fall . Note: you will not get as many blooms in the Fall as you would in the Spring and you will have to keep an eye out for slug damage which is less of an issue in Spring.

Where to Plant

Ranunculus like to be Well watered but they do not like to be stuck in standing water or soggy soil as this will cause the corms to rot so selecting sites with good drainage is a must.

Ranunculus like Full Sun in the Spring and Fall months, but will suffer from the excessive heat from full sun exposure in July thru August so extra care should be taken when selecting your planting location for Late Summer – Fall blooms to one that will provide shade at the hottest part of the day in Summer.

A bunch of dried Ranunculus Buttercup corms.
  • Your new ranunculus corms look like brown little dried up “octopuses”. This is normal. Keep them in the paper bag in which you received them and store in a cool dry place until you are ready to start them for the season.
  • To Wake Up your corms before planting you will need to soak them for approximately 3 hours in room temperature water. Once finished soaking, the corms will be almost doubled in size.
  • Now you can either plant them directly outside if the weather conditions are right or pre-sprout indoors. Pre-sprouted corms will flower sooner than direct planted. If direct planting then you would plant them out 1 month before expected Last Frost Date, be prepared to cover small shoots when temperatures below 0C expected. (Direct planting will work better for Zones 4 + or if starting in late Spring for blooms at end of Summer/Early Fall.
  • To Pre-sprout indoors start about 2 – 3 weeks prior to planting out. Half fill a 4 inch pot or seed tray if sprouting multiple plants. Place the corms on the soil “tentacles” down and cover with potting soil. Cover the tray/ pot to protect from insects and rodents and keep in a cool location around 4-10 C for 2 weeks. Ensure soil is moist but not soaking wet.
  • During the pre-sprouting the corms will continue to increase in size and will start to develop thin white hairy roots. Once these roots are about 1/2″ long you can plant them out in the garden or in a larger container.
  • Plant in location with full morning and evening sun and shade from the hot midday sun. Soil should be prepared with compost and fertilizer. Soil should be well draining but not dry or overly wet.
  • Cover when temperatures below zero expected and watch for slugs as they will strip the leaves quickly reducing the health of the plant and number of blooms.
    Ranunculus normally starts to flower about 90 days after planting. Late winter started corms will flower by mid-spring and continue for four to six weeks.
    The vase life of ranunculus is often more than 10 days. For the longest vase life, cut when buds are colored and squishy, like a marshmallow, but not open.
A handful of freshly lifted Ranunculus corms in Fall. These will be cleaned of dirt and allowed to dry out before storing in a paper bag for the winter to be planted in the following Spring.

Save Corms for Next Spring by gently lifting them from the soil in the Fall after the plants have finished blooming. Snip off any remaining foliage and gently brush off dirt. Place on a tray and allow to dry out for a few days, brush off any remaining dirt and place in a paper or mesh bag and store in a cool, dry location until the following year and follow the above instructions.

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