Seed Patrol
To tell if cannabis seeds are viable, sprout some and count. A mature seed is usually hard, dark to grey, and survives a firm squeeze, but looks only hint. A damp paper towel test, run the way Iowa State University Extension describes for garden seed, gives a number: seeds sprouted divided by seeds tested.
This is an evergreen how-to. This desk read the pages quoted below on 24 October 2026.
How to tell if cannabis seeds are viable by look and feel
Royal Queen Seeds’ seed quality page says size and shape are not a quality sign; colour and feel say more about maturity. Hard, dark-to-grey seeds that take a firm press are likely mature.
Does the float test work?
Partly. Royal Queen Seeds says to wait one to two hours, and to run it only if you will germinate straight afterwards, because sunk seeds have taken in water. The Arnold Arboretum’s Expedition Tool Kit, a woody-plant field guide, tells collectors to confirm float results with cut tests.
How to test cannabis seed germination rate
Iowa State’s method is written for garden seed and never mentions cannabis:
- Count out at least 20 randomly picked seeds; 50 is better, 100 best.
- Roll them, separated, in several layers of premoistened paper towel.
- Bag the roll, label it, and keep it at 70 to 80 F.
- Check at two or three days, then daily for a week or so.
- A seed has germinated when a root or cotyledon breaks the coat. Divide germinated by tested.
Iowa State calls 90% or more very good for most species.
What a test on a small pack can tell you
A pack smaller than Iowa State’s 20-seed minimum can only be tested coarsely. This is this desk’s arithmetic on Iowa State’s formula:
| Seeds tested | Each seed moves the result by |
|---|---|
| 3 | about 33 points |
| 5 | 20 points |
| 10 | 10 points |
| 20 (Iowa State’s minimum) | 5 points |
Iowa State says carefully handled test sprouts may be planted. A small test says whether the packet is alive. Royal Queen Seeds calls planting the one true test, so for most packs the germination run is the test. See also our storage guide and planting depth guide.
Frequently asked questions
How can you tell if cannabis seeds are good or bad?
Start with feel. Royal Queen Seeds says mature seeds are hard, very dark to light grey, sometimes striped, and survive a firm press; immature ones tend to be green and soft. A germination test gives a count: seeds sprouted divided by seeds tested.
Do bad cannabis seeds float?
Often, but not reliably. Royal Queen Seeds says floaters after one to two hours are more than likely poor. The Arnold Arboretum’s field guide says viable seeds generally sink but results should be confirmed. None of the three pages read gives an accuracy figure for cannabis.
What colour are healthy cannabis seeds?
Royal Queen Seeds describes mature seeds from very dark, almost black, to very light grey, sometimes with tiger-like stripes. Green, soft seeds that break under light pressure tend to be immature. Size and shape, it says, are not a quality sign.
Check your local laws before you buy or germinate cannabis seeds. Seed Patrol writes for adults growing where home cultivation is lawful.