Diagnosing a Seed That Won't Germinate: The 6-Check Method

Diagnosing a Seed That Won't Germinate: The 6-Check Method

Facing a sowing that won't come up, don't panic — a methodical diagnosis identifies the cause in minutes. Here are the 6 checks to review, from the seed itself to the sowing conditions, according to established gardening practice.

Contents

• 1 — The viability test
• 2 — Examining the sown seeds
• 3 — Substrate temperature
• 4 — Moisture state
• 5 — Depth and oxygen
• 6 — The elapsed delay
• Symptom table
• Frequently asked questions

1 — The viability test: is the seed alive?

First reflex: test a sample from the same batch. Place 10 seeds on moistened absorbent paper in a half-closed bag, at 20-24 °C, and watch:

• 8 seeds out of 10 swell and deform (the radicle expands) → 80% germination expected: the batch is good, the problem is in the conditions.
• Fewer than half respond → consider replacing the batch, or sow much denser to compensate.
• No emergence a week after the normal delay on the packet → replace the seeds.

2 — Examining the sown seeds

Gently dig up a few seeds from the failed sowing:

• Soft, browned or rotten → damping-off or excess water + cold.
• Hard and intact for a long time → dormancy (impermeable coat, need for cold).
• Dry → the substrate dried out during emergence.

3 — Substrate temperature

• Below ~18 °C → warmth-loving seeds rot rather than germinate; pepper and aubergine refuse to emerge below 18 °C.
• In open ground below 7 °C → no germination; wait for warmer soil and the end of frost.
• Above 25-30 °C → cool species (spinach, lettuce) refuse to emerge.
• Quick diagnosis: a thermometer or heat mat reveals and fixes the problem in one go.

4 — Moisture state

• Soggy substrate (water drips when squeezed) → rot and suffocation of seeds.
• Dry substrate (crumbles to powder) → imbibition never started.
• Wet-dry-wet cycle → the sprouting germ withered during the dry phase.
• Target: evenly moist, never soggy.

5 — Depth and oxygen

• Correct depth: 2-3 times the seed's diameter. Too deep = lack of oxygen.
• Compacted or saturated substrate → seeds lack air.
• Prolonged soaking (>24-48 h without rinsing) → suffocation.

6 — The elapsed delay

Last check before condemning the sowing: has the species' normal time passed? Radish emerges in 2-4 days, celery in 3 weeks, parsley in a month. Most annuals: 3-10 days. No emergence a week after the delay on the packet = negative verdict.

Symptom table

Symptom	Likely cause
Seeds missing from soil, soft, rotten	Damping-off, excess water, cold soil
Seedlings emerged then wilting, collapsed, collar lesions, white down	Damping-off
Seeds intact and hard for a long time	Dormancy — soaking, scarification or cold required
Nothing emerges, seeds dry	Substrate dried out or never imbibed
Nothing emerges, substrate correct	Dead seeds, too deep, or insufficient delay

Frequently asked questions

How to know if a seed is dead?

The 10-seed test on moist paper kept warm: swollen and deformed = alive; intact after double the normal delay = probably dead or deeply dormant.

Why do seeds emerge then die?

That is damping-off: fungi kill the seedling at the collar. Proven prevention: sterile substrate, disinfected containers, sparse sowing, bottom watering, lid removed at emergence.

Can I re-sow in the same spot?

Yes, after correcting the cause: temperature raised, excess water removed, fresh sterile substrate — and seeds tested alive.

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