Short answer
Cannabis seeds that won't germinate are usually too cold, too wet, too dry or too old. Fresh seed shows a taproot in 1–5 days at 22–27 °C (72–81 °F); old seed can take up to 10 days. Fix the temperature and moisture before blaming the seed. Supported.
Why
Germination speed is set by temperature. Hemp seed germinates across roughly 19–30 °C, with an optimum near 29.6 °C, and slows sharply on a cold windowsill [1].
A seed needs oxygen as well as water. Long soaks and waterlogged towels or plugs suffocate the embryo and favour the rot organisms that cause damping-off [4].
Seed age and storage matter. Seeds kept cold and dry at about 5 °C (41 °F) held their germination capacity for around six years; warm, humid storage costs viability far sooner [3].
Old, slow seed can sometimes be pushed. Germinating in 1% hydrogen peroxide in the dark gave faster, higher germination than water, including for very old seed [2].
The numbers
| Factor | Good | Problem |
|---|---|---|
| Temperature | 22–27 °C (72–81 °F) | Below ~18 °C (64 °F): slow or stalled |
| Soak | ≤ 24 h | Over 24–36 h: oxygen starvation |
| Time to taproot | 1–5 days fresh seed | Nothing after 10 days |
| Storage | ~5 °C (41 °F), dry, airtight | Warm, humid, bright |
What to do
- Measure the temperature where the seeds sit, not the room. Aim for 22–27 °C.
- Keep towels damp, not dripping; plugs moist, not wet.
- Wait 10 days before giving up on older seed.
- For old stock, try 1% hydrogen peroxide in a closed tube in the dark [2]. Gloves and eye protection when diluting stronger peroxide.
- Run a 10-seed test on a batch before planting the lot.
Common mistakes
- Germinating on a cold windowsill or floor.
- Soaking for days "until it cracks".
- Letting a paper towel dry out once the shell has split.
- Storing seed in a warm drawer for years, then blaming the breeder.
Related
- Full article: Germination methods compared
- Seed viability and storage
- Do floating seeds mean duds? · Do seeds need light to germinate?
- Terms: germination · radicle
