Does freezing damage seeds?
Written by
Paul Reynolds
Reviewed by
Prof. Samuel Fitzgerald, Ph.D.When done properly, freezing seeds preserves their viability for a very long time. Properly dried seeds with a moisture content of less than 8% can be safely frozen without risk of injury. Ice crystals form only in seeds that have excess moisture, causing the cells to rupture. It is the practice of professional seed banks to freeze at 0° F. (-18° C.) for long-term preservation.
Before freezing, the moisture content of seeds is critical. Use silica gel packs or oven-drying methods to reduce the moisture content of the seeds to below 8%. Test the seeds for dryness by bending them. If they snap rather than bend, they are dry. My heirloom tomato seeds are stored in vacuum-sealed bags with dessicants to prevent ice damage before being frozen.
When freezing seeds, viability is considerably enhanced compared with refrigeration. At 0°F, seeds will remain viable 5-10 times longer than at refrigerator temperature. Tropical seeds, such as tomatoes and peppers, appear to be significantly improved in their vitality through freezing. Freezing practically suspends the cellular metabolic processes, thereby conserving the genetic material of the plant.
Home Freezer Method
- Temperature: 0°F (-18°C)
- Preparation: Seeds below 8% moisture in airtight containers
- Viability extension: 5-10x longer than room temp
- Best for: Long-term storage of garden seeds
Deep Freeze Method
- Temperature: -4°F (-20°C)
- Preparation: Vacuum-sealed with oxygen absorbers
- Viability extension: 10-20x longer
- Ideal for: Rare seed preservation
Cryopreservation
- Temperature: -320°F (-196°C) liquid nitrogen
- Preparation: Professional dehydration protocols
- Viability extension: Centuries
- Used by: National seed banks
Proper thawing of seeds is essential to maintain viability, and frozen packets should be placed in the refrigerator 24 hours before being opened at room temperature. This gradual warming up prevents the condensation that necessarily occurs on the seeds. Do not refreeze thawed seeds, as moisture will collect during the thawing process. The thawed seeds should be used immediately for planting or testing.
Some seeds are more tolerant of freezing than others. Tomatoes, peppers, beans, and flowers stand well in freezing conditions, but seeds containing oil, such as those of sunflowers, are liable to become rancid over time. Frozen seeds should be tested every 2 to 3 years to determine if any changes in viability are occurring. The freezing of seeds is a significant improvement in seed storage methods, provided it is done properly.
Read the full article: Seed Viability Test Guide: Ensure Your Seeds Grow
