Skip to content
NatureHQ

mechanism

Germination

Germination is water going in and a root coming out. It needs water, oxygen and a suitable temperature — not soil — and a dormant seed is not waiting passively but being actively held back until a cue arrives.

Two things about germination are consistently got backwards. The first is what it requires: not soil, but water, oxygen and a temperature the seed will accept. Seeds germinate on damp paper, in gutters and inside fruit, running entirely on reserves packed inside them — soil matters afterwards, for the seedling. The second is what dormancy is. A dormant seed looks inert and is not; it is holding itself back with active hormonal machinery, and will not germinate even in perfect conditions until a specific cue arrives. That cue is a prediction about the world. Months of cold confirms that winter has genuinely happened, so the seed does not sprout in a mild November. A particular molecule in smoke confirms that fire has passed and the canopy has gone. Passage through a gut, abrasion, a flush of nitrate, a change in day length — each is a seed checking that the conditions it is about to bet its entire stored energy on are the ones it evolved for.

Developed record · 58% complete · reviewed 2026-08-10

What this page covers

A process rather than an organism. Covers seed plants; dormancy classes and cues vary enormously between floras.

Quick facts

What it needs
Water, oxygen, suitable temperature — not soil
Complete when
The radicle breaks through the seed coat
Dormancy
Actively maintained, hormonally, until a cue arrives
Fire cue
A single smoke molecule, active at 1 part per billion

Three phases, and a definition that surprises people

Germination is water going in and a root coming out — everything green happens afterwards

Established

Specialists would state this without hedging. Multiple independent lines of evidence agree.

Germination proceeds in three phases: rapid imbibition of water; a plateau during which metabolism resumes, stored reserves are mobilised and cells prepare to elongate; and a resumption of water uptake as the radicle elongates and ruptures the seed coat. Radicle emergence marks the completion of germination; seedling establishment is a subsequent process.

Who this applies to
seed plants generally
Studied in
Angiospermae

You may have heard

“Seeds need soil to germinate”

They need water, oxygen and a suitable temperature — which is why seeds germinate on damp paper, in gutters and inside fruit. Soil supplies those conveniently and supplies nutrients the seedling needs afterwards, but germination itself runs entirely on reserves already inside the seed.

Why we rate it this way, and what the caveats are
EstablishedHigh confidence

Foundational seed physiology, directly measurable as a water-uptake curve, and consistent across species.

How far it can be extended

The triphasic water-uptake pattern and radicle-emergence definition hold across seed plants, with species differing in timing and requirements.

Caveats

  • A seed that imbibes and then fails is not "partly germinated" — germination is defined by radicle emergence.
  • Species differ enormously in how long each phase takes.
  • Soil is not required; water, oxygen and a suitable temperature are.

Still unanswered

  • What determines the length of the metabolic plateau across species?

Last reviewed 2026-08-10

The evidence (1 study)

  • Supports · primary

    Seed germination and dormancy

    Bewley, 1997 · The Plant Cell

    The canonical account of the three phases and the events within each.

  1. Imbibition: the dry seed takes up water rapidly and swells. This is physical, and happens in dead seeds too — which is why swelling is no evidence of viability.
  2. The plateau: water uptake stalls while metabolism restarts, mitochondria are repaired or built, and enzymes begin dismantling stored starch, oil and protein into usable form.
  3. Radicle emergence: water uptake resumes as cells elongate, and the embryonic root pushes through the seed coat. At this point germination is, by definition, complete.

Everything people picture as germination — the shoot, the first leaves, anything green — happens after germination has finished. Those belong to seedling establishment, which is a different process with a different failure mode: germination runs on the seed’s own reserves, and establishment requires the seedling to start supplying itself.

What happens next

  • Photosynthesis

    What a seedling must start doing before its reserves run out

  • Seed dispersal

    How the seed got there, and why the location matters

Words used here
Imbibition
The physical uptake of water by a dry seed. It happens whether or not the seed is alive.
Radicle
The embryonic root. The first thing to emerge, and the marker that germination is complete.
Cotyledon
A seed leaf. In many species it is the food store; in others it is pushed up and does the first photosynthesis.

Dormancy is a bet about the future

A dormant seed is not asleep — it is being actively held back until a cue arrives

Established

Specialists would state this without hedging. Multiple independent lines of evidence agree.

Dormancy is an actively maintained state, controlled substantially by the balance between abscisic acid and gibberellins, and released by specific environmental cues. Recognised classes — physiological, physical, morphological and combinations — map onto habitat, with cold stratification prevalent in temperate floras and hard-coat physical dormancy in fire-prone and seasonally arid systems. Dormancy depth is itself modulated by conditions during seed maturation on the parent plant.

Who this applies to
seed plants, with dormancy class varying by habitat and lineage
Studied in
Angiospermae
Why we rate it this way, and what the caveats are
EstablishedHigh confidence

Well-established seed physiology with a characterised hormonal basis, supported by the ecological correspondence between dormancy class and habitat.

How far it can be extended

Dormancy classes and their ecological distribution are documented across floras on several continents.

Caveats

  • Dormancy classification schemes differ between authors.
  • Molecular mechanisms are characterised in detail for very few species.
  • A seed that fails to germinate may be dormant, dead or simply in the wrong conditions, and telling these apart requires testing.

Still unanswered

  • How is dormancy depth set during seed maturation?
  • How long can seeds of long-lived soil seed banks actually persist?

Last reviewed 2026-08-10

The evidence (3 studies)

A seed germinating has one shot. It spends everything it has on producing a root and a shoot, and if the conditions are wrong it dies. Dormancy is the mechanism that stops it spending on a false signal — a warm week in February, a shower in a drought.

Dormancy classes and the cue that releases each
ClassWhat holds the seed backWhat releases it
PhysiologicalHormonal balance inside the embryoProlonged cold (stratification), after-ripening, light
PhysicalA seed coat impermeable to waterAbrasion, fire, freeze–thaw, passage through a gut
MorphologicalAn embryo not yet fully developed at sheddingTime and suitable conditions for it to finish
CombinationalBoth a hard coat and a hormonal blockBoth cues, usually in sequence

Each requirement encodes a prediction. Cold stratification is a seed confirming that a real winter has passed, so that germination lands in spring rather than in an autumn warm spell. A hard coat needing abrasion is a seed that will not start until something has physically happened to it — often passage through an animal, which also moves it somewhere new.

Words used here
Stratification
A period of cold, moist conditions required before some seeds will germinate. Gardeners reproduce it in a fridge.
Scarification
Breaking or abrading a hard seed coat so water can enter. Fire, gut passage and grit all do it naturally.
Seed bank
Viable seed lying dormant in soil, sometimes for decades, waiting for a cue. It is why disturbed ground greens up so fast.

How you find out what a seed is waiting for

Dormancy classes are not read off the seed. They are established by giving it things and seeing what works.

A seed that will not germinate is usually waiting for information, not damaged

Established

Specialists would state this without hedging. Multiple independent lines of evidence agree.

Seed dormancy comprises several distinct classes. Physical dormancy is an impermeable seed coat relieved by abrasion, fire or temperature cycling; physiological dormancy is a block within the embryo relieved by warm or cold stratification; morphological dormancy reflects an underdeveloped embryo; and combinational forms occur. The cue required to break dormancy corresponds to the environmental conditions under which a seedling of that species can survive.

Who this applies to
seed plants, best characterised in temperate floras
Studied in
Angiospermae, Gymnospermae

You may have heard

“Old seeds do not work”

Seed that fails to come up has often not been given the cue it requires — a cold period, a scratch through the coat, a fire. Age matters too, but "nothing happened" is more often a missing signal than a dead seed.

Why we rate it this way, and what the caveats are
EstablishedHigh confidence

A large classification supported by direct experiment: applying the predicted treatment breaks dormancy and withholding it does not.

How far it can be extended

Dormancy classes have been assigned across thousands of species worldwide, though tropical floras are less well sampled.

Caveats

  • Dormancy class is inferred from response to treatments, so unusual mechanisms can be mislabelled.
  • Laboratory conditions rarely reproduce the microsite a seed actually experiences.
  • Temperate floras are far better characterised than tropical ones.

Still unanswered

  • How will dormancy-breaking cues tied to winter cold behave as winters shorten?

Last reviewed 2026-08-10

The evidence (1 study)

There is no way to look at a dormant seed and see which class of dormancy it has. What can be done is to give identical batches different pretreatments and then germinate them all under the same conditions, so that any difference in outcome belongs to the treatment. The one that works names the mechanism.

How we know

Making a seed believe winter has happened

A seed that will not germinate in warm, moist, well-lit conditions is not obviously alive. What is it waiting for?

The standard design for classifying dormancy is a factorial one: batches of seed from the same collection are given different pretreatments — moist chilling for varying periods, scarification of the coat, warm incubation, exposure to smoke or to light — and then all are moved to identical germination conditions. Because the germination test is the same for every batch, any difference in outcome is attributable to the pretreatment, and the treatment that works identifies the class of dormancy involved.

What happened

Species sort cleanly into classes by which pretreatment works. Physically dormant seed responds to abrasion, heat or fire and not to chilling; physiologically dormant seed responds to weeks of moist cold and not to scarification; some require both, in sequence.

What it shows

That dormancy is a timing mechanism rather than a defect. The cue a seed requires corresponds to the season in which its seedling could survive, so a seed with deep physiological dormancy is effectively counting the winter before committing.

What it does not show

Dormancy class is inferred from which treatment works, so an unusual mechanism can be assigned to the wrong class by responding to a treatment for the wrong reason. Laboratory germination conditions are also nothing like a real seedbed — no fluctuating temperature, no competing seedlings, no pathogens — so germination percentages here say little about what fraction of a real seed crop establishes.

The controls — what makes this evidence rather than a story
  • Untreated seed from the same collection incubated alongside, which is what shows the seed was dormant rather than dead.
  • A viability test — usually tetrazolium staining — on a subsample, separating dormancy from mortality directly.
  • Chilling applied moist, since dry cold does not break physiological dormancy and would confound the result.
  • Identical final germination conditions for every batch, so the pretreatment is the only variable.

From Seeds: Ecology, Biogeography, and Evolution of Dormancy and Germination

The control that matters most in this design is the viability test. A seed that fails to germinate under every treatment might be deeply dormant or might simply be dead, and staining a subsample separates the two — without it, "no germination" is uninterpretable.

This is also the practical answer to the commonest gardening complaint about wildflower seed. A packet that "did not work" has usually been sown in spring without the months of moist cold the species requires, and the seed is not dead — it is still waiting.

Words used here
Stratification
Holding seed moist at a particular temperature — usually cold — for weeks or months to break physiological dormancy.
Viability test
A chemical stain showing whether an embryo is alive. It is what separates a dormant seed from a dead one.

Why a seed crop does not germinate all at once

Seeds from the same plant, the same year and the same pod do not behave identically. Some germinate on the first suitable occasion, some in the second year, some after five. That variation is not sloppiness in the mechanism — it is the mechanism.

An annual plant in an unpredictable climate faces the possibility that any given year is a total failure: the rain stops, the seedlings die, nothing sets seed. A lineage that germinated everything at the first opportunity would be wiped out by one such year. A lineage that holds part of each crop back survives it, at the cost of a lower average rate of increase. Spreading germination across years is insurance, paid for in growth.

The stored, still-viable seed in the soil is the seed bank, and in some habitats it is enormous — tens of thousands of seeds per square metre, most of them older than the plants growing above. It is why cleared ground produces a flush of species nobody planted, and why the plants that appear after a fire or a landslip were mostly already there.

The Beal experiment, begun in 1879, buried bottles of seed to be dug up at intervals. Seeds of moth mullein were still germinating when a bottle was opened in 2021, 142 years later.

Words used here
Bet-hedging
Accepting a lower average return to reduce the chance of total failure. Spreading germination over years is the classic plant example.
Seed bank
The viable seed lying dormant in soil. Often far older and more diverse than the vegetation above it.

Seeds that wait for fire

Some seeds wait for fire, and detect it by a single molecule in smoke

Well supported

Good evidence backs this, though some details remain open.

Bioassay-guided fractionation of smoke-derived water identified a butenolide, karrikinolide, active in promoting germination of fire-responsive species at concentrations as low as one part per billion. Synthetic compound reproduces the response. The molecule is a product of the combustion of plant material.

Who this applies to
fire-adapted floras, identified in Western Australian species
Studied in
Conostylis aculeata, Stylidium affine
Why we rate it this way, and what the caveats are
Well supportedHigh confidence

The compound was isolated by repeated fractionation and the response reproduced with pure synthetic material, which is as direct as chemical attribution gets.

How far it can be extended

Karrikin responsiveness has since been documented across fire-prone floras on several continents, though responsiveness varies widely between species.

Caveats

  • Karrikins are one of several germination-active components of smoke.
  • Responsiveness varies enormously between floras and species.
  • Heat, charred wood and nutrient pulses are separate fire cues acting alongside this one.

Still unanswered

  • How do seeds perceive karrikins?
  • Why do some non-fire-adapted species respond to them too?

Last reviewed 2026-08-10

The evidence (2 studies)

How we know

Splitting smoke until one molecule was left

Water that smoke has been bubbled through makes fire-adapted seeds germinate. Smoke contains thousands of compounds — which one is doing it?

A mixture cannot be understood by analysing it, because the analysis returns everything at once. The method used instead was bioassay-guided fractionation: separate the smoke water into fractions, test each on seeds, discard the fractions that do nothing, and re-separate whichever still works. Repeat until a single compound remains, then determine its structure and synthesise it to confirm that the pure substance reproduces the effect.

What happened

The active agent is a butenolide, later named karrikinolide, effective at concentrations as low as one part per billion. Pure synthetic compound reproduced the germination response.

What it shows

A single small molecule, produced by the combustion of plant material, acts as a germination cue. The biology is elegant: it cannot be produced by anything except plant matter burning, which is exactly the reliability a seed needs before staking its only reserves on a signal.

What it does not show

Karrikins are one of several germination-active components of smoke, and heat, charred wood and post-fire nutrient pulses are separate cues acting on different species. Responsiveness varies enormously between floras. The experiment identified the compound; it did not establish how seeds perceive it.

The controls — what makes this evidence rather than a story
  • Every fraction was tested on seeds at each round, so activity was tracked rather than assumed to follow the largest component.
  • Untreated water gave the baseline germination rate.
  • Synthetic compound was tested against the natural fraction — the confirmation that the right molecule had been isolated.

From A compound from smoke that promotes seed germination

The logic is precise. A fire removes the canopy, releases nutrients and clears competitors — a brief window in which a seedling has light and space it will not get again for years. A seed that can detect that window and germinate into it is enormously better off than one germinating at random.

What makes the cue reliable is that the molecule is a breakdown product of burnt cellulose. It cannot be produced by anything except plant material burning, which is exactly the property a signal needs if a seed is going to stake its life on it.

Heat, smoke, charred wood and the nutrient pulse after a fire are separate cues acting on different species. Some seeds need the heat and ignore the smoke.

Words used here
Karrikin
The class of butenolide molecules in smoke that trigger germination in fire-adapted plants.

Dispersal is not reproduction until this happens

A seed that travels a kilometre and lands on rock has achieved nothing. Dispersal and germination are two halves of one problem, and the connections between them are direct.

  • Gut passage scarifies hard coats while it moves the seed — the same event does both jobs.
  • A cached seed is buried at roughly the depth a seedling needs, by an animal with no such intention.
  • Ant-dispersed seeds arrive in nest soil that is bare, fertile and protected from fire.
  • Wind-dispersed seeds are small, so they carry little reserve and must establish fast or not at all.
  • Dormancy times germination to the season, having let dispersal handle the place.

The full reproductive chain

What is still unsettled

  • How long can seeds in a soil seed bank actually remain viable?

    Why it matters: Records of centuries exist for a few species and the general limits are unknown, which matters for restoration and for what a disturbed site will regrow as.

  • How is dormancy depth set while the seed is still on the parent?

    Why it matters: Conditions during maturation alter how deeply dormant a seed will be, which means a parent plant is in some sense forecasting for its offspring.

  • How do seeds perceive karrikins?

    Why it matters: The receptor pathway is only partly characterised, and it may be a repurposed hormone system rather than a dedicated one.

The research behind this page

7 studies, newest first. Each one has a page explaining what it found and what it could not show.

You may also find this interesting

What this page is still missing

NatureHQ publishes its own gaps. This record is at 58% completeness against what we would call a finished subject.

  • no research from the last few years is attached — check for newer work
  • no popular claim about this subject has been checked yet
  • Seedling establishment — what happens after germination — is referred to constantly and not covered.
  • Practical propagation is heavily searched and deliberately treated only in principle.
  • Seed viability testing and longevity in storage are absent.

Last reviewed 2026-08-10 · 5 claims · 0 search questions answered on this page