Introduction
The "90% germination" label on a packet may not reflect actual germination after storage. A quick 3–5 minute germination test provides actionable viability data for adjusting sowing density.
Key terms:
- Germination rate: the percentage of seeds that produce normal seedlings under optimal conditions
- Germination test: a rapid assessment of the current viability of a seed lot before large-scale sowing
- Seed lot: seeds of one species, variety, and harvest year from one supplier
Standard Germination Test: 5-Minute Protocol
Materials:
- 10 or 20 seeds (20 gives greater accuracy)
- Two layers of moistened paper towel or cloth
- A container or zip-lock bag
- A marker for the date
Procedure:
- Count out 10 or 20 seeds, selecting evenly from different parts of the packet
- Distribute evenly between two moist (not wet) towel layers
- Place in a container at the optimal germination temperature for the crop (typically 22–24°C for microgreens)
- Check after the standard germination period for the crop
- Count normally germinated seeds (well-formed shoot, visible root, no rot or deformity)
Standard germination periods:
- Radish, rocket, brassicas: 48–72 hours
- Sunflower, pea: 3–5 days
- Corn, beetroot: 4–7 days
- Basil, coriander: 4–6 days
Calculating the result: with 10 seeds, the number germinated = the percentage. With 20 seeds: (germinated ÷ 20) × 100.
Adjusting Sowing Density Based on Test Results
Mathematical approach: if the standard density is calculated for 90% germination but the test shows 70%, multiply the density by 90÷70 (≈1.28).
Practical guidelines:
- 85–95% germination: use standard density
- 70–84% germination: increase by 15–20%
- 55–69% germination: increase by 30–40%
- Below 55% germination: purchase a new lot or use for non-food purposes
Germination Vigour: An Additional Assessment
Germination rate tells you "how many will germinate." Germination vigour tells you "how evenly and quickly." A lot with 90% germination rate but low vigour will produce staggered emergence over 3–4 days instead of uniform emergence within 24–36 hours.
Vigour indicators:
- Uniform germination within a single day at the correct temperature = high vigour
- Germination spread over 2–4 days = reduced vigour
- Thin, weak seedlings despite adequate germination rate = reduced vigour from storage damage
Three Mistakes That Cost the Most
Testing only 5–6 seeds: minimum 10 seeds for practical decisions; 20 for accuracy.
Testing at winter room temperature: winter indoor temperature (17°C) slows germination; use temperature-controlled conditions.
Skipping tests for "reliable" suppliers: germination rate varies between lots from the same supplier due to storage conditions, harvest year, or variety changes.
Correct Testing Protocol
Every new seed lot requires testing before production. Record results (date, crop, lot number, germination percentage). When germination is below 85% — adjust and document the sowing density. When germination is below 70% — make the decision before committing to production.