Batch tested germination: what the figure really means

More and more product pages state that the seed has been tested. Batch tested germination sounds reassuring, yet what the figure actually means often stays unexplained. This article covers how such a test works and how to read the result.

What a batch actually is

A batch is one harvest of seed from the same parent plants, collected and processed at the same time. Every pack from that batch therefore comes out of the same container.

A test on one batch consequently says something about every pack from it. A test on a different batch of the same line, however, says nothing about yours.

How the test is carried out

A random sample is taken, usually one hundred seeds. Those are placed under fixed conditions: constant temperature, moist substrate and a set running time.

Afterwards the tester counts how many seeds produced a root within that period. That percentage is the result.

Why the conditions are fixed

Only fixed conditions make two batches comparable. Change the temperature or the duration and the number changes with it, even though the seed is identical.

For that reason a serious result always comes with its method. A percentage without context is worth very little.

What the number does not tell you

A germination test measures whether a seed sprouts, and nothing else. About stability, yield or aroma it says absolutely nothing.

It also says little about seedling vigour. A seed can just barely sprout and still produce a weak plant.

Why your own result may come out lower

At home the conditions are rarely as stable as in a test. Temperature swings, overly wet substrate and sowing too deep all cost germination.

A laboratory test also counts every visible root, while you are only satisfied with a plant that keeps growing. Those two standards differ.

The role of seed age

A test always carries a date. Seed that tested at 95 percent a year ago sits lower today, even in good storage.

Ask for the test date rather than the percentage alone, therefore. A classic such as Super Silver Haze feminized is often produced in larger batches, which makes the date particularly relevant.

Why a sample is enough

A batch of ten thousand seeds is never tested in full, since nothing would remain to sell. Instead a random sample stands in for the whole.

That only works when the sample is genuinely random. Anyone picking the best-looking seeds is measuring their own selection rather than the batch.

With one hundred seeds tested, the margin of error runs to a few percent. A difference between 92 and 95 percent therefore means little, while a gap between 60 and 90 percent clearly means something.

Sprouting versus growing on

A seed that puts out a root counts as a success in a test. At home the work only begins there, because the seedling still has to surface and stay upright.

Losses at that stage rarely come from the seed. Sowing too deep, soaking the medium and providing too little light are the usual causes.

Running your own test

You can reproduce it at home, provided you work consistently:

• Take ten seeds from the same pack, not the best-looking ones.
• Place them between damp kitchen paper on a plate.
• Keep the temperature around twenty to twenty-five degrees.
• Count how many show a root after seven days.

Repeat that identically for every new batch. You are then comparing batches rather than moods.

What counts as a good percentage

Serious suppliers usually sit above ninety percent on fresh seed. Between eighty and ninety remains workable, particularly with older stock.

Below seventy percent it becomes awkward, because you structurally need more seed than planned.

Testing and feminized seed

Feminized seed germinates no differently from regular seed. Batches are often smaller, though, which makes testing relatively more expensive.

Some suppliers therefore test only periodically. In that case, ask whether your specific batch was tested.

What to do with a disappointing result

Write down your own conditions before making contact. Temperature, method, dates and seed count are the details that matter.

Then test a line you know as a control, for instance Royal Moby feminized. If that germinates normally, your method is probably not the problem.

Storage between purchase and sowing

Seed left for months in a warm drawer loses vigour. Cool, dry and dark storage slows that considerably.

A sealed container in the fridge works well, as long as you let it warm before opening. Otherwise moisture condenses on the seeds.

Why suppliers publish different things

Some shops put the percentage on the product page, while others mention it only on request. That difference says more about their workflow than about quality.

What matters is whether they can back the figure up. A line such as Granddaddy Purple feminized is sold by many suppliers, so comparing is worth the effort.

How a guarantee relates to a test

A germination guarantee and a germination test are two different things. The test describes what a batch did in the lab, while the guarantee describes what the shop does when things go wrong at your end.

Read both, therefore. A high test figure without any guarantee is perfectly fine, and a generous guarantee without a figure is workable too, yet the combination offers the most certainty.

How much seed to plan for

Always plan a little above the number of plants you want. At ninety percent germination plus some losses afterwards, ten seeds usually leave you with eight usable plants.

That sounds obvious, though plenty of growers still count exactly. A single failed seed then puts the whole schedule under pressure.

What appearance can tell you

Ripe seed is usually dark, hard and lightly striped. Pale green or white seed was often harvested unripe and germinates less reliably.

Appearance is no guarantee either, however. An unremarkable seed from a well-tested batch typically beats a handsome seed with no information attached.

How the test is run

A laboratory takes a sample from the lot and germinates it under ideal humidity and temperature. That is not your drawer and not your medium. Therefore the figure describes the potential of the lot rather than what will happen at home. Consequently a lower result in your own kitchen rarely means fraud.

Sample size matters

A rate calculated on twenty seeds means far more than one calculated on five. By contrast, very few listings mention that detail at all. Therefore ask. In fact the answer tells you a great deal about how serious the supplier is.

The date of the test

Seed loses vigour over time even when stored well. Consequently a test run three years ago no longer describes the current lot. Therefore look for a date beside the percentage and treat its absence as a warning.

Running your own test

Germinate ten seeds under identical conditions and count how many open within four days. In addition, repeat the same method with every new lot you buy. Therefore after a few purchases you hold your own baseline and stop depending on the label.

What lowers germination at home

Water that is too cold, compacted medium and excessive planting depth explain most domestic failures. None of those causes has anything to do with the lot itself. Therefore repeat the process with room temperature water and one centimetre of depth before complaining. Consequently the rate usually climbs straight away.

Frequently asked questions

Does one hundred percent mean everything will come up?

No. It means every tested seed produced a root under test conditions, which is not the same as a healthy plant.

How often should a batch be tested?

At harvest and periodically afterwards, since germination declines over time.

Can I still use an old pack?

Often yes. Run a small test with a few seeds before planting a whole cycle.

Are small, pale seeds always worse?

Not always, although dark, firm seeds germinate somewhat more reliably on average. The link is weaker than people assume.