Why germination rate matters (and why 100% is a myth)
If you have ever sown a packet of twenty rare seeds and watched only seven come up, you may have felt a small pang of failure. Set that feeling aside. In the world of seeds, especially rare and wild species, partial germination is not a mistake — it is biology doing exactly what it evolved to do. This chapter will teach you to read germination rate as a diagnostic tool rather than a report card, so you can tell the difference between a bad batch, a bad technique, and a species that is simply cautious by nature.
Germination rate is simply the percentage of viable seeds that produce a seedling under given conditions. If you sow 40 seeds and 26 emerge, your rate is 65%. That single number hides a great deal, and learning to interpret it is one of the most useful skills a grower can develop.
Realistic numbers by seed type
Expectations should be calibrated to the plant. A commercial hybrid tomato and a wild alpine primula live in different universes. Here are honest ranges you can use as a mental baseline — real results vary with seed freshness, storage and your own conditions.
- Fresh vegetable and annual seed (tomato, lettuce, zinnia): often 80–95% when fresh and well stored.
- Common perennials and herbs: typically 50–80%.
- Hard-coated or dormant wild species (many legumes, Canna, Geranium): 20–60% even done correctly, because dormancy is staggered on purpose.
- Rare alpines, orchids, and slow tree species: 5–40% is often a genuinely good result.
- Old or poorly stored seed: expect a steep drop — a seed that germinated at 70% two years ago may test at 25% today.
Viability versus germination: two different questions
A seed can be alive (viable) yet refuse to germinate because a dormancy mechanism is still locked. So a low germination rate can mean the seed is dead — or that it is very much alive and simply waiting. Distinguishing these saves you from throwing out good seed.
The two quick field tests every grower should know:
- Float test (rough): drop seeds in water for a few hours. Many floaters are empty or non-viable, but this is unreliable for corky or oily seeds — treat it as a hint, not a verdict.
- Cut test (better): slice 3–5 spare seeds with a blade. A firm, plump, white or pale-green interior means viable; a shrivelled, hollow, brown or mouldy interior means dead. This one test explains most 'failures'.
- Tetrazolium or germination test (best): for precious seed, sow a small test batch of 10–20 on damp paper towel in a sealed bag at the species' ideal temperature and count over 2–4 weeks.
How to actually measure your rate
Guessing 'about half' is not good enough if you want to improve. Do a small, controlled paper-towel test so your number means something.
- Count out a known number — 20 seeds is the practical minimum for a meaningful percentage.
- Fold them into a moist (not dripping) paper towel and seal in a labelled zip bag with the date.
- Hold at the species' target temperature — commonly 18–22 °C for temperate species, 25–28 °C for many warm-climate species.
- Check every 2–3 days, mist if it dries, and remove any mouldy seed immediately.
- Record the day each seed sprouts. Stop counting once no new seed has moved for 14 days.
- Divide sprouts by seeds sown, times 100. That is your real germination rate under your conditions.
Reading the pattern, not just the number
The shape of germination over time tells you more than the final figure. Keep a simple log with dates, and watch for these signatures:
- Fast and uniform (most seeds in days 4–10): healthy, fresh, correctly treated seed — well done.
- Slow trickle over weeks or months: normal for dormant wild species; be patient and do not disturb the pot.
- Strong start then sudden stop with mould: too wet, too warm, or poor airflow — a technique problem, not a seed problem.
- Nothing at all after the expected window: either the dormancy trigger was never satisfied (missing cold, light, or scarification), or the seed was dead. Do a cut test to tell which.
Factors that quietly lower your rate
When your number is below the published range, one of these is usually the culprit. Work through them in order before blaming the seed:
- Age and storage: most seed loses viability year by year. Warm, humid storage accelerates death; a cool, dry, dark jar slows it dramatically.
- Missed dormancy treatment: skipping cold stratification (e.g. 6–8 weeks at 3–5 °C in a fridge) or scarification.
- Temperature off target: even 5 °C too high or low can halve germination in fussy species.
- Sowing depth: as a rule, sow at 2–3 times the seed's diameter; tiny light-dependent seeds must sit on the surface, not buried.
- Damping-off fungus: kills seedlings after emergence, making a good rate look poor.
- Water quality and overwatering: the single most common killer of germinating seed.
Setting expectations you can live with
For rare species, plan around the rate rather than fighting it. If a species germinates at roughly 30% and you want six plants, sow at least 20 seeds — and ideally in two staggered batches so a single mishap cannot cost you everything. Buying or collecting a little extra seed is far cheaper than a lost year.
A gardener measures success not by the seeds that failed, but by understanding why each one did what it did.— Quinta dos Ouriques University
Germination rate is a conversation with the seed, not a scoreboard. When you learn to read it — the number, the timing, and the pattern — a 'disappointing' 40% becomes useful information rather than a verdict. In the next chapter we will take these diagnostics and turn them into targeted fixes for the most common failure modes, so your next sowing gives you the best chance your seed and conditions allow.