Watch the episode · 5:59Sandpaper the shell. Chill them in the fridge. Never use tap water. And if a seed hasn't cracked in two days, bin it. These are germination rules growers swear by, and you have probably heard them all. Here are seven of them, checked against the research, with a verdict on each.
The short answer ▶ 0:24
- 015 myths
some cost you seeds
- 022 half true
right, for a reason
Five are myths, and some of them can cost you good seeds. Two are half true. The place to start is the one that throws away the most good seeds.
Myth 1: no sprout in 48 hours? ▶ 0:34
“No sprout in 48 hours? it's a dud”Myth
Good seeds can take a week or more
Du et al., Life (2022)If a seed hasn't cracked in 48 hours, it's a dud? Plenty of good seeds take longer. In a lab study from China, hemp seeds sat in plain water at 20 °C. By day 3, 61% had sprouted. By day 7, 87%. A second variety went from 51% to 80%. So about a third of the good seeds came up after day 3.
one hemp variety at 20 °C · a second went from 51% to 80%
Source · Du et al., Life (2022)
That is why official seed tests for hemp keep counting until day 7. And a Slovenian study found even that can be too early: it suggested day 12 for a final count. So give a slow seed a week, or even two, before you give up on it. If nothing shows after that, why didn't my seeds sprout? goes through the usual causes.
Source · ISTA Rules · Kocjan Ačko & Baričevič, Acta Agric. Slov. (2004)
Myth 2: slow seeds, weak plants? ▶ 1:15
“Slow seeds grow weak plants”Half True
Maybe an old batch, not a lost plant
Finch-Savage & Bassel, J. Exp. Bot. (2016)A seed that's slow to sprout will grow a weak plant? Half true. Seed scientists do use speed as a sign of vigour. As seeds age, they sprout more slowly, so a whole pack of slow starters can mean old or tired seed.
But in crops, a late start mostly hurts when the plant is crowded by its neighbours. Nobody has followed slow cannabis seeds through to harvest. A late seedling in its own pot has nothing to compete with, so give it time before you judge it.
Source · Finch-Savage & Bassel, J. Exp. Bot. (2016)
Myth 3: scratch the shell ▶ 1:51
“Scuff the shell so water gets in”Myth
No gain for most seeds, and it can cost you some
McDonald & Lubell-Brand, HortTechnology (2025)Scratch the shell with sandpaper, or nick it, so water can get in? A myth, for most seeds. No one has tested sandpaper on cannabis. But in 2025, a University of Connecticut team tested a stronger version: fresh seeds soaked in acid for 10 minutes to thin the shell. It took one seed line from 60% to 30%, and another from 81% to 43%. Only one, with bigger seeds, did better: 38% to 63%. Left in longer, nearly everything got worse.
| Untreated | 10 min in acid | |
|---|---|---|
| Seed line 1 | 60% | 30% |
| Seed line 2 | 81% | 43% |
| Seed line 3 (big) | 38% | 63% |
Source · McDonald & Lubell-Brand, HortTechnology (2025)
And cutting off the seed's tip? That comes from a University of Guelph lab study. Their seeds were washed in strong bleach, then sat in sterile jelly, and the uncut ones barely sprouted. Cutting off the tip got every one up within a week. That is a fix for a lab problem. In damp soil or a paper towel, a healthy seed doesn't need it, and the tip is where the root comes out.
Source · Pepe, Hesami & Jones, Plants (2021), CC BY 4.0
Myth 4: hormone booster soaks ▶ 2:47
“A hormone soak boosts any seed”Half True
Helps under stress, but didn't beat enough water
Du et al., Life (2022)Soak your seeds in a growth hormone called gibberellic acid, and they will all come up? Half true: it can help a seed in tough conditions. In the same Chinese study, seeds with enough water sprouted at 87%. Under lab drought, seeds soaked in plain water managed 53%. Soaked in the hormone, 79%.
all soaked 8 h first · drought made in the lab · GA = gibberellic acid, 400 mg/L
So it helped under stress, but it didn't beat simply having enough water. The researchers never tested it in good conditions, and the strongest dose did less good than a medium one.
Source · Du et al., Life (2022)
Myth 5: the fridge trick ▶ 3:24
“Chill seeds in the fridge before sowing”Myth
No significant difference after a month
McDonald & Lubell-Brand, HortTechnology (2025)Chill your seeds in the fridge, damp, before you sow them, to wake them up? The same Connecticut team kept seeds in damp sand at 4 °C for a month. Compared with seeds kept dry at room temperature, there was no significant difference in any of the three lines. Earlier studies that chilled hemp seed for three to five days found no boost either.
| Chilled 30 days | Kept dry | |
|---|---|---|
| Seed line 1 | 87% | 75% |
| Seed line 2 | 82% | 84% |
| Seed line 3 | 72% | 54% |
Source · McDonald & Lubell-Brand, HortTechnology (2025)
Where the fridge does help is storage. In that Slovenian study, 3-year-old hemp seed kept dry in the fridge still sprouted at 65%, against 46% at room temperature. So chill them dry for keeping, not damp for sowing. There is more on that in how long do cannabis seeds last?
Source · Kocjan Ačko & Baričevič, Acta Agric. Slov. (2004)
Myth 6: tap water and chlorine ▶ 4:03
“The chlorine in tap water kills seeds”Myth
No effect, even at 77 times tap levels
Frink & Bugbee, HortScience (1987)The chlorine in tap water will kill your seeds? Drinking water usually carries 1 mg of chlorine per litre, or less. In a Connecticut study, vegetable seeds were watered with up to 77 mg per litre, and germination wasn't affected at any level.
vegetable seeds · germination unaffected at every level
Growing seedlings were more sensitive, but pepper and tomato only slowed at 8 mg per litre, still about eight times tap levels. So plain tap water is fine for germinating. What matters far more is keeping the seeds moist, not soaking wet.
Source · Frink & Bugbee, HortScience (1987)
Myth 7: must the root point down? ▶ 4:43
“The root must point straight down”Myth
Sideways is fine: roots find down
Singh et al., Front. Plant Sci. (2017)When you plant a sprouted seed, the root has to point straight down? Roots find their own way down. Tiny starch grains in the root tip settle to the lowest side within minutes. That tells the root which way is down, and it curves to follow. In maize trials, seeds laid flat came up just as fast and evenly as seeds planted root down.
Source · Singh et al., Front. Plant Sci. (2017) · Torres et al., Exp. Agric. (2011)
What you shouldn't do is plant it root up near the surface. In one tree-seed study, some upside-down seeds sent their roots into the air, and those seedlings stayed small and died. So root down, or laid on its side, about 1 cm deep, as covered in seedling stuck in its shell.
Source · Marlangeon, Rev. FCA UNCuyo (1969)
The final score ▶ 5:23
- No sprout in 48 hours? It's a dudMyth
- Slow seeds grow weak plantsHalf True
- Scuff the shell so water gets inMyth
- A hormone soak boosts any seedHalf True
- Chill seeds in the fridge firstMyth
- Tap water's chlorine kills seedsMyth
- The root must point straight downMyth
Five myths and two half truths. A healthy seed mostly needs water, air, warmth and a little patience. Most of the tricks do nothing, and some of them cost you seeds.
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Sources
- Du, G., Zhang, H., Yang, Y., Zhao, Y., Tang, K. & Liu, F. (2022). "Effects of Gibberellin Pre-Treatment on Seed Germination and Seedling Physiology Characteristics in Industrial Hemp under Drought Stress Condition." Life 12(11): 1907. doi:10.3390/life12111907 (CC BY 4.0)
- Kocjan Ačko, D. & Baričevič, D. (2004). "Influences of seed age and storage conditions on germination ability of hemp seed (Cannabis sativa L. var. sativa)." Acta agriculturae Slovenica 83(1): 85-94.
- International Seed Testing Association, International Rules for Seed Testing (Cannabis sativa: first count day 3, final count day 7).
- Finch-Savage, W.E. & Bassel, G.W. (2016). "Seed vigour and crop establishment: extending performance beyond adaptation." Journal of Experimental Botany 67(3): 567-591. doi:10.1093/jxb/erv490
- McDonald, M.M. & Lubell-Brand, J.D. (2025). "Cold Moist Stratification and Acid Scarification Do Not Significantly Enhance Hemp Seed Germination." HortTechnology 35(4): 552. doi:10.21273/HORTTECH05682-25
- Pepe, M., Hesami, M. & Jones, A.M.P. (2021). "Machine Learning-Mediated Development and Optimization of Disinfection Protocol and Scarification Method for Improved In Vitro Germination of Cannabis Seeds." Plants 10(11): 2397. doi:10.3390/plants10112397 (CC BY 4.0)
- Frink, C.R. & Bugbee, G.J. (1987). "Response of Potted Plants and Vegetable Seedlings to Chlorinated Water." HortScience 22(4): 581-583. doi:10.21273/HORTSCI.22.4.581
- Singh, M., Gupta, A. & Laxmi, A. (2017). "Striking the Right Chord: Signaling Enigma during Root Gravitropism." Frontiers in Plant Science 8: 1304. doi:10.3389/fpls.2017.01304
- Torres, G.M., Vossenkemper, J.P., Raun, W.R. & Taylor, R.K. (2011). "Maize (Zea mays) leaf angle and emergence as affected by seed orientation at planting." Experimental Agriculture 47(4): 579-592.
- Marlangeon, R.C. (1969). "Posición de siembra en Araucaria angustifolia y su influencia sobre el crecimiento de la planta." Revista de la Facultad de Ciencias Agrarias (UNCuyo) 15(1): 74-89.
Every claim in this article comes from the episode script, which is checked against these papers. Prices on Seedscanner are dated observations; this page is not growing or legal advice.
