# Do cannabis seeds need light to germinate?

> No. Cannabis seeds do not need light to germinate; they need warmth (22–27 °C / 72–81 °F), moisture and air, and germinate well in the dark. Light becomes essential the moment the seedling breaks the surface: start at about 100–200 µmol/m²/s for 18 hours, rising to 150–300. A seedling left in the dark after emerging stretches and weakens within a day or two.

- Canonical: https://genetixbay.com/knowledge/answers/do-seeds-need-light-to-germinate.html
- Topic: Germination · Type: How-to
- Evidence: Supported · Status: Draft: awaiting expert review
- Full article: [Germination methods compared: soak, paper towel, plugs, direct sow](https://genetixbay.com/knowledge/germination/germination-methods.md)
- Also asked as: Should seeds germinate in the dark or the light? | Do cannabis seeds need light? | Should seeds be kept in the dark? | How much light does cannabis need?
- Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)"

## Short answer

No. [Cannabis seeds](https://genetixbay.com/knowledge/glossary/achene.md) [germinate](https://genetixbay.com/knowledge/glossary/germination.md) in the dark; they need warmth (22–27 °C / 72–81 °F), moisture and air. Light matters from the moment the [seedling](https://genetixbay.com/knowledge/glossary/seedling.md) breaks the surface, starting at about 100–200 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md) for 18 hours. *Supported*.

## Why

A germinating [seed runs](https://genetixbay.com/knowledge/glossary/seed-run.md) on its own stored reserves, not [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md). A standard cannabis protocol germinates seeds in closed tubes in the dark and only moves them under light once sprouted [1].

Temperature, not light, sets the pace. [Hemp](https://genetixbay.com/knowledge/glossary/hemp.md) germinates fastest in roughly the 19–30 °C band and slows sharply in the cold [2].

Once the shoot emerges, the reserves run out fast. Young plants given enough daily light produce better roots and more mass; below a [DLI](https://genetixbay.com/knowledge/glossary/dli.md) of about 8 mol/m²/day plugs of other crops were inferior [3].

Later on, light is the biggest yield lever indoors: flower yield rose linearly with light from 120 to 1,800 µmol/m²/s in one trial [4].

## The numbers

| Stage | PPFD (µmol/m²/s) | Hours | DLI (mol/m²/day) |
|---|---|---|---|
| Germinating seed | None needed | Dark is fine | 0 |
| Emerging seedling | 100–200 | 18 | 6–13 |
| Seedling, [true leaves](https://genetixbay.com/knowledge/glossary/true-leaves.md) | 150–300 | 18 | 10–19 |
| Veg | 300–700 (up to ~900) | 18–24 | 19–58 |
| Flower | 800–1,200 | 12–13 | 35–56 |

## What to do

1. Germinate in a warm, dark place: a cupboard, or a tub on a gentle heat mat.
2. Check daily for a [taproot](https://genetixbay.com/knowledge/glossary/taproot.md); plant at 0.5–2 cm.
3. Put the planted seed under the light straight away, or within hours of emergence.
4. Start at 100–200 µmol/m²/s, and raise intensity as true leaves appear.

## Common mistakes

- Germinating on a sunny windowsill that cooks or dries the towel.
- Leaving emerged seedlings in a dark cupboard "one more day".
- Blasting new seedlings with full flowering intensity.

## Related

- Full article: [Germination methods compared](https://genetixbay.com/knowledge/germination/germination-methods.md)
- [PPFD and DLI by stage](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md)
- [What light schedule for seedlings?](https://genetixbay.com/knowledge/answers/light-schedule-for-seedlings.md)
- Terms: [PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md) · [germination](https://genetixbay.com/knowledge/glossary/germination.md)

## Follow-up questions

**How much light does cannabis need?** Cannabis needs about 100–300 µmol/m²/s as a seedling, 50–150 as an unrooted clone, 300–700 (up to about 900) in veg and 800–1,200 in flower, more with added CO2. In a controlled indoor trial, flower yield rose in a straight line from 120 to 1,800 µmol/m²/s with no change in potency. Measure PPFD at the canopy; wattage and lumens don't tell you.

**When do seedlings need light?** A cannabis seedling needs light as soon as its hook or cotyledons break the surface, usually 1–3 days after planting a sprouted seed. Before that, light does nothing for it. Start gentle, around 100–200 µmol/m²/s on 18 hours, and raise it to 150–300 as the first true leaves open. Leaving an emerged seedling in the dark makes it stretch thin and pale.

**Does light hurt germinating seeds?** Light itself doesn't hurt a germinating cannabis seed, but what comes with it can. A lamp or windowsill can heat and dry a paper towel or plug, killing a fresh taproot. That's why towels and tubs are kept in a warm, dark place. Once planted under a light, keep the surface just moist and check the medium temperature stays near 22–27 °C.

## Sources

1. Sorokin A, Yadav NS, Gaudet D, Kovalchuk I, 2021. Development and standardization of rapid and efficient seed germination protocol for Cannabis sativa. Bio-protocol 11(1): e3875. https://doi.org/10.21769/BioProtoc.3875
2. Geneve RL, et al., 2022. Temperature limits for seed germination in industrial hemp (Cannabis sativa L.). Crops 2(4):415–427. https://doi.org/10.3390/crops2040029
3. Runkle E. The benefits of lighted plugs. Michigan State University Extension. https://www.canr.msu.edu/resources/the_benefits_of_lighted_plugs
4. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020