A few kinds of seed need light to germinate
A few kinds of seed need light to germinate, and burying them stops them coming up. Sow these on the surface, pressed into firm, moist soil and left uncovered or barely dusted over. Don't sow them at the depth a larger seed would take.
Promising A person has checked it against its sources. If you skip this, it still grows, just less well. The planner suggests it.
How it works
These seeds carry the light-sensing pigment phytochrome, which must catch light to switch on the hormone cascade that releases the seed to germinate, so a seed buried past a few millimeters sits in the dark with that switch never thrown and stays dormant.
What to do about it
Press light-requiring seed onto firmed, moist soil or medium and leave it uncovered or only barely dusted, then keep the surface damp. A seed sitting on top dries out fast, and a fine mist keeps it in place better than a heavy watering. The plant's page says whether it needs light; a seed that needs darkness is the opposite and is covered as usual.
How much it matters: No germination-rate figure is given. The size of the effect is the difference between a seed left in the light and the same seed buried in the dark, which the sources describe as coming up versus not; because sowing depth is entirely the gardener's own act, the rule only advises.
The evidence
Evidence: checked against 1 source in the research-based literature.
The source
When sowing light-requiring seeds, sow them on the soil surface
Plants it applies to · 3
Read next
How this rule has changed
Every change is dated, newest first. The full record, with each reason, is in the data download.
- Sources updated
- Wording made clearer
- Added to the rules
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Milpa Gardens. “A few kinds of seed need light to germinate, and burying them stops them coming up. Sow these on the surface, pressed into firm, moist soil and left uncovered or barely dusted over. Don't sow them at the depth a larger seed would take.” Evidence grade: Promising. https://milpa.garden/rules/few-kinds-seed-need-light-germinate-burying/
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How we grade evidence
- Well established
- The rule names its mechanism and is settled, by sources a person has read and checked or by plain arithmetic and geometry.
- Promising
- The mechanism is named and the literature backs it. A few questions are still open.
- A good hunch
- Plausible by its mechanism, but field studies are thin, so treat it as a lean.
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- The evidence points both ways, or no study has tested it, so the planner does not enforce it.
- Refuted
- The claim did not survive its sources. It is kept so the folklore can be answered.