Short answer. Seeds need warmth (20–30 °C / 68–86 °F), steady moisture and air. In a hemp study the optimum band was 19–30 °C, with a calculated optimum of ~29.6 °C, base ~3.4 °C and ceiling ~42.6 °C [1]. Any method that holds those conditions works. For fresh seed, direct sow in a moist plug or small pot is simplest and avoids handling the taproot. Use a paper towel or 1 % hydrogen peroxide protocol [3] when you want to see results or rescue old seed.
Methods compared
| Method | How | Pros | Cons | Evidence |
|---|---|---|---|---|
| Direct sow | 0.5–1.5 cm (¼–½ in) deep in moist, light mix or plug | No handling; no transplant of a bare radicle | Can't see what's happening | Grower practice |
| Soak, then sow | 12–24 h in water at room temperature, then plant | Speeds water uptake; sinkers are hydrated | Over 24–36 h risks oxygen starvation | Supported: soaking improved germination in one study [5] |
| Paper towel | Damp (not wet) towel in a closed dish, dark, warm; plant at 0.5–2 cm radicle | Visible; easy germination test | Radicles break; towels dry out or grow mould | Grower practice |
| Rockwool / plug | Pre-soaked cube (pH ~5.5 for rockwool) | Clean start for hydro | Easy to overwater | Grower practice |
| 1 % H₂O₂ protocol | Sterilise, germinate and grow on in 1 % hydrogen peroxide | Faster, higher germination than water, no contamination; helped very old seed [3] | Lab protocol; handle peroxide safely | Supported [3] |
| Tip scarification + disinfection | Remove seed tip after disinfection (in vitro) | 0 % contamination, 100 % germination within a week in a tissue-culture setting [4] | Fiddly; for in vitro work | Supported (lab) [4] |
Results on peroxide and scarification conflict across studies: one found hot-water soaking best and peroxide/scarification largely ineffective [5]. The common thread is: fresh seed germinates well without tricks.
Numbers that matter
| Parameter | Target |
|---|---|
| Temperature | 22–27 °C (72–81 °F); hemp optimum 19–30 °C [1] |
| Base temperature | Roughly 0–7 °C depending on model and cultivar [1][2] |
| Soak time | ≤ 24 h |
| Planting depth | 0.5–1.5 cm (¼–½ in), radicle down |
| Expected time to radicle | 1–5 days fresh seed; up to 10 days old seed |
| Light | Not needed until the seedling emerges |
How to do it (direct sow)
- Moisten a light seedling mix or plug until it holds together but doesn't drip.
- Plant 0.5–1.5 cm deep; cover lightly.
- Keep at 22–27 °C under a humidity dome, but vent daily.
- Turn on light (low intensity, see seedling care) once the hook emerges.
Safety
Hydrogen peroxide above 3 % irritates skin and eyes; wear gloves and eye protection when diluting stronger stock. Bleach (sodium hypochlorite) used for disinfection must be rinsed off and never mixed with acids or ammonia.
Common mistakes
- Soaking for days.
- Paper towels left sopping wet.
- Planting too deep.
- Cold windowsills (below ~18 °C germination slows sharply).
Evidence
Temperature limits are Supported by hemp studies [1][2]. Peroxide and scarification benefits are Supported in lab protocols [3][4] but Contested across studies [5]. Choice of home method is Grower practice.
