# Seed coat

> The protective outer layer of a seed; in cannabis it is fused to the fruit wall and forms the hard shell that cracks open at germination.

- Canonical: https://genetixbay.com/knowledge/glossary/seed-coat.html
- Also written: testa, seed shell, seed hull, shell, hull
- Glossary category: Plant biology · Evidence: Established
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

The seed coat (testa) is the protective layer that forms from the ovule's outer tissues and surrounds the embryo. In cannabis the testa sits tight against the pericarp (the [fruit](https://genetixbay.com/knowledge/glossary/achene.md) wall of the achene), so growers treat the two as one hard shell. It limits water uptake, guards the embryo from injury and microbes, and splits along its seam when the swelling embryo pushes the root out.

## In practice

At [germination](https://genetixbay.com/knowledge/glossary/germination.md) the seed takes up water, swells, and the shell cracks along its edge; the [radicle](https://genetixbay.com/knowledge/glossary/radicle.md) emerges first, often within 24-72 hours at about 22-26 °C (72-79 °F). A [seedling](https://genetixbay.com/knowledge/glossary/seedling.md) that comes up still wearing its shell over the [cotyledons](https://genetixbay.com/knowledge/glossary/cotyledon.md) is a "helmet head". Usually it falls away on its own within a day; misting it and waiting beats prying, which tears the seed leaves.

Scarification (lightly sanding the shell) is sometimes used on old or very hard seed. It is rarely needed for fresh, healthy stock and can let pathogens in.

## Don't confuse with

- **Achene**: the whole fruit; the seed coat is one layer of it.
- **Cotyledons**: the seed leaves inside, not a covering.
- **Endosperm**: stored food tissue inside the seed, not the shell.

## Related terms

[Achene](https://genetixbay.com/knowledge/glossary/achene.md), [Radicle](https://genetixbay.com/knowledge/glossary/radicle.md), [Cotyledon](https://genetixbay.com/knowledge/glossary/cotyledon.md)

## Read more

- [Germination methods compared: soak, paper towel, plugs, direct sow](https://genetixbay.com/knowledge/germination/germination-methods.md)

## Sources

1. Small E. 2015. Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization. The Botanical Review 81:189-294. https://doi.org/10.1007/s12229-015-9157-3