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Columbines are herbaceous perennials that require a cold period for the seeds to germinate. Otherwise, the seeds will remain dormant in the soil. That’s why those who live in a region with warmer winters opt for alternative ways to cold stratify the seeds.
Columbine seed cold stratification usually takes between three and six weeks, depending on the region and the soil conditions. When stratifying seeds indoors, it’s best to leave them in the refrigerator at 40 degrees Fahrenheit (4.4 degrees Celsius) for four to six weeks.
In the rest of the article, I will explain the mechanism involved in columbine seed cold stratification and why it’s necessary. I’ll also provide some steps to ensure your seeds successfully germinate come spring. Read on!
Columbine Seed Cold Stratification Explained
Columbines (Aquilegia spp.) are a group of plants with seeds that enter dormancy before germinating. Although these plants self-sow prolifically, there’s no guarantee that all of the seeds will successfully germinate.
Self-sowing and seed stratification are part of a special plant behavior many species have developed to ensure longevity. Basically, the plant spreads numerous seeds for better chances of survival in the following growing season.
However, since most plants have an optimum temperature required for growth, the seeds shouldn’t germinate in the fall. Columbines are hardy plants, but they die back in late fall or after they go to seed to prepare for next spring’s blooms.
On the other hand, seed stratification is a defense mechanism many herbaceous perennials have that helps them ensure the seeds survive well into maturity once they sprout (source). Since columbines drop their seeds in late summer or fall, the hot or cold soil will signal the seeds that it’s not yet time to germinate.
The Effects of Temperature on Phytohormone Regulation
Various plants have developed chemical reactions through the antagonistic interactions between the phytohormones gibberellic acid (GA) and abscisic acid (ABA), which regulate the germination process among their seeds (source).
Specifically, gibberellic acid signals seeds to break out of dormancy and sprout when the conditions are favorable. On the other hand, abscisic acid encourages the seed to enter dormancy while the environmental conditions are still non-conducive for growth.
Both phytohormones are sensitive to temperature, light, and stress (source). For instance, when the temperatures are too high or too low, the ABA levels increase, preventing the seeds from breaking out of dormancy.
On the other hand, after a sufficient period of cold — approximately four weeks of soil temperatures staying around 40 degrees Fahrenheit (4.4 degrees Celsius) — and an increase in the number of daylight hours, the GA levels will gradually increase. This happens when the cold temperatures remain consistent, followed by a period of warmth.
As the GA levels increase, physical changes will occur in the seeds, allowing them to sprout and grow normally in spring. However, during years when winter temperatures fluctuate drastically, the GA levels will remain low, prohibiting your seeds from germinating for another year.
Some plants, such as peonies, may even have a double dormancy, requiring a cold period followed by a warm period and another cold period before germinating. As a result, it can take around two years before their seeds grow.
Thankfully, columbines only need one cold period to germinate. Still, the seeds can remain dormant indefinitely if the temperatures are unstable. That’s why many gardeners decide to cold stratify their seeds indoors under controlled temperatures.
How To Cold Stratify Columbine Seeds Indoors
To increase your chances of having columbine seedlings in spring, you can cold-stratify your seeds indoors in several ways. But first, you must collect the seeds when they’re ready. Here’s how:
- Wait until the flower or seed pods are dry and crisp.
- Pluck the dried pods off the stems.
- Cut off the tip of the pods to release the columbine seeds. The seeds should appear black and shiny. Sometimes, the pods will open by themselves, so you don’t have to wait until then. Otherwise, the seeds will fall to the ground before you can collect them.
- Allow the seeds to dry completely on a paper towel for a week.
- Store the seeds in a paper bag or an airtight container, such as a mason jar, in a cool and dark area of your house. A kitchen cabinet should do just fine.
Remember that the storage area shouldn’t fall below 50 degrees Fahrenheit (10 degrees Celsius). Come January or February, you can take out the seeds and cold-stratify them using any of the methods below.
In this method, you don’t have to prepare a substrate. You can just wrap the seeds in moist tissue paper and put them in a zip-lock bag. You can then place the bag in the refrigerator. The crisper drawer is suitable for storing your seeds for cold stratification.
However, the refrigerator’s light may switch on whenever you open the door. In that case, you must carefully wrap the seeds in moist tissue paper.
Label the bag with the date and columbine cultivar, and ensure the temperature stays between 37 and 40 degrees Fahrenheit (2.8 and 4.4 degrees Celsius) for four weeks.
Moist Soil Method
To make it easier to transplant your seeds into pots or sprinkle them into your garden in spring, you can use moist sand or vermiculite instead of tissue paper.
Spread the seeds evenly in your chosen substrate. Since columbine seeds are pretty small, you can place two to three seeds per tablespoon of soil.
Seal the bag and leave it in the refrigerator as you would when using the soilless method.
Seed Starter Tray
Alternatively, you can press one seed per hole on a potting mix in a seed starter tray. You don’t have to cover the seeds completely with soil, but cover the tray with a clear dome to help retain moisture for the seeds.
Leave the setup in the refrigerator for four to six weeks, but mist the dome once every one to two weeks to prevent the soil from drying up.
After six weeks, if the outdoor temperatures aren’t warm enough, you can place the tray indoors, near an eastern window. It can take another three weeks or more for the seeds to germinate.
Note that this method is only suitable if you have an extra refrigerator to avoid contaminating your other refrigerated food supplies.
Columbine seeds typically need at least a month of cold temperatures ranging from 37 to 40 degrees Fahrenheit (2.8 to 4.4 degrees Celsius) for better chances of germination. Depending on the climate in your area, you may need to stratify them indoors under controlled conditions. Otherwise, they will remain dormant in the soil.