Every grow starts with a seed or a cutting, yet this is one of the least-studied stages of cannabis cultivation. Most germination research so far has been done on industrial hemp seed, so treat those numbers as a starting point rather than a rule for drug-type genetics.
Hemp seed germinated fastest and most completely in a warm band of roughly 19–30 °C (66–86 °F). In seed lots that germinated poorly, carefully removing the hard seed shell rescued many more seeds, but that was tested on weak lots, not fresh seed.
For clones, the controlled studies agree on a few practical points. A rooting hormone substantially improved rooting compared with none, while the exact hormone strength made little difference in one large hemp trial. Trimming leaf tips reduced rooting success, and the rooting medium mattered more than the hormone. Cuttings taken from new shoots on recently tissue-cultured plants (“retips”) rooted well even without hormone.
Gaps we’re still filling: controlled studies on seed storage, pre-soaking methods and rooting humidity for drug-type cannabis.
Key terms
IBA (rooting hormone)
Indole-3-butyric acid, a synthetic plant hormone used in rooting gels and powders to help cuttings form roots.
Retip cutting
A cutting taken from new shoots on a plant that was recently grown from tissue culture.
Drug-type vs. hemp
Drug-type cannabis is grown for high THC. Hemp is legally limited to low THC and is often grown for CBD, grain or fiber. Research on one doesn’t always apply to the other.
Studies
5 studies
Temperature Limits for Seed Germination in Industrial Hemp (Cannabis sativa L.)
Crops · 2022
Hemp
Controlled experiment
Open access
Germination was fastest and most complete between about 19 °C and 30 °C (66–86 °F).
Authors: Robert L. Geneve, Evan W. Janes, Sharon T. Kester, David F. Hildebrand, Derrick Davis
2(4):415–427
Study plant: Two industrial oilseed hemp cultivars (‘Georgina’ and ‘Victoria’), lab germination tests
Researchers germinated hemp seed at constant temperatures from 3 °C to 42 °C to map how warmth affects sprouting speed and success. Seeds germinated best and fastest between roughly 19 °C and 30 °C, with a calculated optimum near 29.6 °C, a floor around 3.4 °C and a ceiling around 42.6 °C. Priming the seeds before sowing made them sprout faster but did not raise the final germination percentage.
Seed Priming and Pericarp Removal Improve Germination in Low-Germinating Seed Lots of Industrial Hemp
Crops · 2022
Hemp
Controlled experiment
Open access
Removing the seed shell raised germination by about 38% in poor-germinating seed lots.
Authors: Jia W. Tan, Sharon T. Kester, Kai Su, David F. Hildebrand, Robert L. Geneve
2(4):407–414
Study plant: Low-germinating industrial hemp seed lots, lab germination tests
The team worked with hemp seed lots that germinated poorly and tested two rescue techniques: priming (a controlled pre-soak) and carefully removing the hard outer shell. Both sped up early germination, but removing the shell did more for the final result, raising germination in weak seed lots by about 38% on average compared with intact seed.
Ex Vitro Rooting of Cannabis sativa Microcuttings and Their Performance Compared to Retip and Stem Cuttings
HortScience · 2022
Hemp
Controlled experiment
Retip cuttings rooted at 76–81% without any rooting hormone.
Authors: Lauren E. Kurtz, Lillian N. Borbas, Mark H. Brand, Jessica D. Lubell-Brand
57(12):1576–1579
Study plant: Two CBD-type cultivars (‘Abacus’ and ‘Wife’) grown in a greenhouse
This study compared plants grown from lab tissue-culture “microcuttings,” regular stem cuttings from mother plants, and “retip” cuttings taken from new shoots on recently tissue-cultured plants. Retip cuttings rooted at 76–81% with no rooting hormone, similar to what hormone-treated stem cuttings achieve. Once the tissue-culture plants were given one extra week of vegetative growth, all three propagation methods produced equivalent plants and flower weight.
Evaluation of substrate composition and exogenous hormone application on vegetative propagule rooting success of essential oil hemp (Cannabis sativa L.)
PLOS ONE · 2021
Hemp
Controlled experiment
Open access
The rooting medium had the biggest effect, and any hormone beat no hormone by 15–18×.
Authors: Sean M. Campbell, Steven L. Anderson, Zachary T. Brym, Brian J. Pearson
16(7):e0249160
Study plant: Eight high-CBD hemp cultivars, cuttings rooted for 12 days in a climate-controlled room
Researchers rooted cuttings from eight high-CBD hemp cultivars across four propagation media and five commercial rooting hormones, then measured root number, length and mass after 12 days. The medium mattered most: rockwool far outperformed the other media. Any rooting hormone improved rooting 15- to 18-fold over none, but hormone strength and application method made little difference. Some cultivars simply rooted better than others.
Vegetative propagation of cannabis by stem cuttings: effects of leaf number, cutting position, rooting hormone, and leaf tip removal
Canadian Journal of Plant Science · 2018
Drug-type cannabis
Controlled experiment
Trimming leaf tips lowered rooting success from 71% to 53%.
Authors: Deron Caplan, Jonathan Stemeroff, Mike Dixon, Youbin Zheng
98(5):1126–1132
Study plant: Drug-type cannabis stem cuttings, 12-day rooting trial in a growth chamber
This trial tested common cloning habits side by side: how many leaves to leave on a cutting, whether to trim the leaf tips, whether the cutting came from the top or bottom of the mother plant, and a synthetic IBA rooting gel versus a willow-extract gel. Trimming leaf tips cut rooting success from 71% to 53%. Cuttings with three leaves grew better-quality roots than two-leaf cuttings, and the IBA gel outperformed the willow product.