Cannabis Seed Float Test: Does It Work?
The cannabis seed float test means dropping seeds in water and watching which ones sink. Many growers read sinking as a sign of a viable seed, but no peer-reviewed cannabis study has tested floating against sinking seeds, so treat the float test as a rough check, not a germination predictor.
What Is the Cannabis Seed Float Test?
The float test is a home check. A grower drops seeds into a glass of plain water and watches whether each one sinks or stays on the surface. The idea is that a seed full enough to sink is ready to sprout, and a seed that floats is empty or old. It is quick and costs nothing, which is why it shows up on so many grow forums. It does not replace a normal start, so most growers move every seed on to germinating cannabis seeds in a paper towel, plug or soil anyway.
Do Floating Weed Seeds Germinate?
Sometimes. A floating seed can still sprout, and a sinking seed can still fail. There is no tested accuracy figure for the float test. What the research does measure is seed maturity. In a 2025 hemp study, mature seeds germinated at 84.67 percent in Petri dishes, against 14.67 percent for immature seeds and 6.67 percent for semi-mature seeds (Turkish Journal of Agriculture). That points to maturity, not float position, as the thing that matters.
Why Can a Good Seed Float?
Growers often suggest that air trapped in or around a dry shell can hold a seed on the surface for a time, though this has not been tested. The same hemp study describes mature seeds as having a hard, brown seed coat and an average 1,000 seed weight of 17.04 grams, while immature seeds averaged 6.89 grams (Turkish Journal of Agriculture). The study did not test whether seeds float or sink, so it cannot show that a floating seed is a dud.
Float Test Signs and What to Do Next
| What you see | What it may mean | What to do next |
|---|---|---|
| Seed sinks soon after it goes in the water | Growers often treat this as a hopeful sign | Germinate it the normal way. Do not treat it as proven viable. |
| Seed stays on the surface | Possibly air in or around the shell, untested | Give it more time, then germinate it the same way as the others. |
| Seed sinks after a short soak | The shell may have taken on water | Move it to a paper towel, starter plug or soil. |
| Seed looks pale, cracked or damaged | Condition may matter more than float position | Note it and compare how it does against intact seeds. |
| Some seeds float and some sink | Variation within one pack is common | Start both groups the same way and compare results yourself. |
| You want a better check than floating | Look and storage history are other clues | Check shell color, hardness and how the seeds were stored. |
What Is a Better Check Than the Float Test?
Look at the seed and its history. Mature seeds in the hemp study had a hard, fully colored coat, while immature seeds stayed green (Turkish Journal of Agriculture). How seeds were kept also matters, and our guide to seed storage mistakes covers heat, light and moisture. If a seedling comes up weak, rule out problems covered in our seedling diseases guide before blaming the seed. Read the germination guarantee to see what applies to your order.
Looking for a fresh pack to start with? Browse our feminized seeds.
Sources
Some sources below studied hemp or other crops rather than drug-type cannabis. Their findings are reported as results for those crops or settings.
No germination promise comes with this float test page, which Kind Seed Co rests on a hemp seed maturity study as general growing information.
FAQ
How long should seeds sit in water for a float test?
There is no tested soak time for the float test. Many growers check once after a short soak and again later, then move every seed to a normal germination method. A seed that is still floating at that point is not automatically a dud and can be started too.
Should I throw away seeds that float?
No. A floating seed can still sprout, and growers often suggest air in or around the shell can keep a sound seed on the surface. Start floating and sinking seeds the same way and judge them by whether they sprout and grow.
Can soaking seeds hurt germination?
There is little research on how long a soak can last before it causes harm. Many growers keep the float step short and move seeds into a moist paper towel, plug or soil once they sink. If you soak at all, use clean water and keep the soak short.
What does a viable cannabis seed look like?
In a 2025 hemp study, mature seeds had a hard brown seed coat and germinated far better than immature seeds, which had a green coat. Color and hardness are useful clues, but no look test confirms that a seed will sprout. Storage history is another clue, and the germination guarantee page sets out what applies.
