Short answer
Cannabis seeds stop germinating for a short list of reasons. The seed stayed too wet and suffocated. The temperature sat below 65°F or climbed past 85°F. The seed was immature, old, or crushed. Or the medium dried out before the taproot broke through. Fix water and temperature first, then inspect the seed itself.
direct sowing vs paper towel cannabis germination
Check the seed before you change anything
Run these four checks so you do not chase a growing problem when the seed was dead on arrival.
How Long Do Cannabis Seeds Take to Sprout?
- Shell and color: viable seeds are dark brown to gray with a hard, mottled shell. Pale green or white seeds were pulled before they matured and almost never germinate.
- Age: seeds stored cool and dry stay viable for two to five years. Seeds left in a warm drawer lose viability in months.
- Crush test: pinch a spare seed between your fingers. A healthy seed resists and cracks with a snap. A seed that turns to powder was dead.
- Sink test: drop seeds in a glass of water. Seeds that still float after a few hours are often hollow, though some viable seeds float at first.
Cause 1: The medium is too wet
A seed takes in water to start, then needs oxygen to convert stored energy into a root. Leave it in standing water or a soaked paper towel and the seed coat softens, bacteria move in, and the seed rots before a taproot shows. Keep the medium damp like a wrung out sponge, never dripping.
Cause 2: Temperature is out of range
Germination runs best between 70°F and 78°F. Below 65°F the process slows to a crawl and mold has more time to win. Above 85°F the embryo can cook. A heat mat on a thermostat or the top of a refrigerator both work. Avoid windowsills, which swing hot and cold.
Cause 3: Bad storage killed the seed
Heat, humidity, and light break down a seed's stored energy. A sealed container in the refrigerator door with a desiccant pack holds viability for years. A plastic bag in a garage through a summer does not.
Cause 4: Rough handling cracked the shell
Squeezing a seed to test it, dropping it on a hard counter, or poking the emerging taproot all end germination. Once the root tip shows, it is the only root the seed gets. Move the seed with tweezers at the shell, never at the root.
Cause 5: Planted too deep
Plant at one quarter to one half inch deep. Deeper than that and the sprout exhausts its stored energy before it reaches the surface. A light dusting of soil over the seed is enough.
Cause 6: Water quality and pH
Chlorinated tap water slows microbial activity the seed needs, and water outside pH 6.0 to 7.0 stresses the emerging root. Use filtered or bottled water at room temperature. Cold water shocks the seed.
Cause 7: The medium dried out
A paper towel left in open air or a peat pellet on a heat mat dries in hours. Check moisture twice a day during germination and mist only when the surface feels dry to the touch.
How to germinate cannabis seeds step by step
- Wet two paper towels with filtered water and squeeze each one until it stops dripping.
- Lay the first towel on a plate.
- Space seeds two inches apart on the towel.
- Cover the seeds with the second towel.
- Invert a second plate over the first to hold humidity.
- Place the covered plates in a dark spot at 70°F to 78°F.
- Lift the top towel every 12 hours to check for a taproot.
- Plant the seed in soil once the taproot reaches one quarter to one half inch.
If you prefer direct planting, skip the towels. Fill a small pot with light seed-starting mix, water it until damp, set the seed one quarter inch deep, and cover the pot with a humidity dome.
How long germination should take
Fresh seeds show a taproot in 24 to 72 hours. Seeds that spent a year in storage can take five to seven days. If a seed has not cracked by day seven, leave it in place and keep the medium damp.
When to give up on a seed
Give every seed 14 days. After that window, the seed is dead or the shell is too hard to open. Toss it and germinate the next one. Do not reuse the same wet towel or the same standing water, since rot spreads from seed to seed.