How To Meet Cold Stratification and Dark Requirements in Seed Starting

March 09, 2023

How To Meet Cold Stratification and Dark Requirements in Seed Starting

Indoor seed starting is a common practice among gardeners who want to ensure their plants have a head start in the growing season. This is especially true for annual cut flowers, which can be grown from seed to bloom in just a few months. However, some annual cut flowers have special requirements when it comes to seed starting. In this blog post, we'll explore two of these special circumstances: cold stratification and dark requirements.

Cool loving flowers at Rooted Flowers

Cold stratification is a process that some seeds require to break their dormancy and germinate. It involves exposing the seeds to a period of cold, usually in a moist environment, before planting. This mimics the natural conditions that the seeds would experience in the wild during the winter months.

Some annual cut flowers that we use cold stratification with are poppies, larkspur, nigella, bells of ireland, and scabiosa. We even cold stratify eucalyptus. To cold stratify seeds, we start by placing them in a damp paper towel and store in the refrigerator for the recommended period of time, generally 2-4 weeks. The length of time required for cold stratification varies by plant species, so be sure to check the seed packet for specific instructions. When in doubt, cold stratify for a month.

Then, I’ll open the bag and rest it on top of my grow lights. I usually see roots forming within 48 hours. They are then planted into a cell tray and grown on under the lights.

Note: If it’s a cool loving flower, it likely needs some sort of cold treatment. When not sowing seeds, keep dry in the fridge.

Cool loving flowers at Rooted Flowers

We are all guilty of trying to start a seed that requires the dark to start but instead put them under lights or in direct sunlight. This is your time to turn it around! The absence of light triggers a hormonal response in the seeds that promotes germination. Seeds that require darkness to germinate are often small and fine, and are best started indoors.

Buplureum and cynoglossum are a must for us with dark requirements. By covering these seeds with a sheet of foil and achieve nearly 100% germination every time. Be sure to keep the soil moist, but not waterlogged, during the germination period. Once you cover with foil, you should not have to water again until a day or two after after it's been lifted.

Dark requirement method in seed germination with foil

Within 3-4 days at the proper temperature, expect little sprouts to start popping up. It's ok to lift the foil to check, but make sure to seal it up again. Once I see 80% germination, I'll remove the foil and place the sprouts in light. They will look pale at first, but green up within 24 hours. 

Pale sprouts under grow lights.

If you're planning on starting annual cut flowers from seed indoors, it's important to be aware of any special requirements they may have. Cold stratification and dark germination are two common special circumstances that some annual cut flowers require. You will increase your chances of success and enjoy a beautiful bounty of flowers by following these tricks!


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