Bonsai seeds are put in the fridge primarily to simulate a cold winter period, a process known as cold stratification, which is crucial for breaking their natural dormancy and significantly increasing their germination rate.
The Science Behind Cold Stratification
Many tree species, especially those native to temperate climates, have evolved to require a period of cold before they will sprout. This natural mechanism prevents seeds from germinating during a warm spell in autumn or winter, which would likely result in the delicate seedlings dying from subsequent frost. By exposing the seeds to cold temperatures, you are essentially telling them that winter has passed, and it's safe to start growing.
- Mimicking Natural Conditions: If you're growing bonsai trees from seed that originate from different climates or if you're planting outside of their natural season, replicating this cold period becomes necessary.
- Breaking Dormancy: The cold treatment helps to soften the seed coat and/or alter chemical inhibitors within the seed that prevent germination.
- Improving Germination Rate: This simulated winter period significantly boosts the number of seeds that successfully sprout, leading to a higher yield of seedlings.
How to Prepare Bonsai Seeds for Refrigeration
To effectively stratify bonsai seeds in your refrigerator, follow these general steps:
- Soaking: Most tree species require you to soak their seeds in water for a period before placing them in the fridge. This softens the outer shell and helps in the absorption of water, which is necessary for germination.
- Moist Storage: After soaking, the seeds are typically placed in a moist medium, such as peat moss, sand, or a damp paper towel, inside a sealed plastic bag or container. This ensures they remain hydrated throughout the cold period.
- Refrigeration: Store the prepared seeds in your refrigerator (typically at temperatures between 35-45°F or 1-7°C) for one to two months. The exact duration can vary depending on the specific tree species.
- Monitoring: Periodically check the seeds to ensure the medium remains moist and to look for any signs of mold. If mold appears, you might need to re-soak the seeds, use a fresh medium, and ensure proper air circulation.
Once the stratification period is complete, the seeds are ready to be planted in a suitable potting mix, and with proper care, they should begin to germinate.
