Short answer. Keep seeds dry, cold, dark and airtight. Small & Brookes recommended ~5 °C (41 °F) to maintain germination capacity for about six years [1]; the general seed rule holds for cannabis: life span rises predictably as temperature and seed moisture fall [3]. Hemp seed at ≤ 25 °C (77 °F), ≤ 70 % RH (≤ 10 % seed moisture) stayed safe for more than 26 weeks [2], so room-temperature storage is fine for a season, not for years. Before planting a precious batch, run a 10-seed germination test.
What's happening
A seed is a living embryo running a very slow metabolism. Heat and moisture speed up the chemical ageing of membranes and DNA. Drop either and ageing slows dramatically. Repeated warming and cooling causes condensation, which is the hidden killer of fridge-stored seeds.
Numbers that matter
| Storage | Expected | Evidence |
|---|---|---|
| ~5 °C (41 °F), dry, airtight | ~6 years with good germination | Supported [1] |
| ≤ 25 °C, ≤ 70 % RH (≤ 10 % moisture) | > 26 weeks safe | Supported [2] |
| Freezer (−18 °C / 0 °F) | Likely longer, only if seeds are dry before freezing | Grower practicebeing reviewed |
| Warm, humid, light | Viability falls within months | Supported [3] |
| Seed moisture target | ~6–8 % for long storage (≤ 10 % for short term [2])being reviewed |
How to store
- Keep seeds in their original sealed packet or a small glass vial.
- Add a desiccant packet (silica gel) to the outer container.
- Fridge at 2–8 °C (36–46 °F), not the door. Label with cultivar and date.
- When removing seeds, let the sealed container reach room temperature before opening (prevents condensation).
- Freezer only for dried, long-term stock you won't open often.
Testing viability
- Germination test: 10 seeds on a damp paper towel at 22–26 °C (72–79 °F), in the dark, for 7 days. Count radicles. 8/10 = 80 % germination.
- Old seeds: a 1 % hydrogen peroxide germination protocol gave faster germination and improved germination of very old, low-viability cannabis seeds vs water in one lab protocol [4] (germination methods).
- Seed colour/float test: mature seeds are usually darker and harder, but colour varies with genetics; the float test is unreliable (Grower practice: it mostly measures trapped air).
Common mistakes
- Opening a cold container in a warm room.
- Storing in a grow room or next to a window.
- Buying more seed than you will plant in 2–3 years and storing it warm.
Evidence
Cold, dry storage extending viability is Supported by cannabis-specific studies [1][2][3] and Established in seed science generally. Freezer outcomes for cannabis are less documented.
