Dormancy: the rest period of a viable seed

Dormancy is the rest period of a viable seed: it could germinate but does not, even under good conditions, until some block is lifted. For cannabis the question usually gets a blanket answer, yes or no. The measurements do not allow one. They come out differently for South African landraces than for European industrial hemp, and the dividing line runs by origin and age of the material rather than by method.

The finding in landraces

Five landraces from KwaZulu-Natal were tested against a water control with seven pre-treatments: potassium nitrate, hydrochloric acid, hot water at 70 Β°C, nitric acid, dry chilling at 10 Β°C, gibberellic acid and sulfuric acid. Viability had been established beforehand by tetrazolium test, so the seeds were demonstrably alive.

The most effective were gibberellic acid, potassium nitrate and dry chilling. From that pattern the authors infer physiological dormancy in the genotypes tested, meaning a block in the embryo rather than in the hull. Anyone sowing such material is therefore dealing with a rest period that can be broken.

The counter-finding in industrial hemp

In industrial hemp the same toolkit does not bite. Cold at 4 Β°C over 72 hours had no effect on germination rate, seedling categories or root measurements in a trial across three cultivars. Short cold treatments of three days at 4 Β°C or five days at 10 Β°C failed to improve germination in 14 industrial hemp cultivars and two others; that compilation is cited in a more recent paper rather than collected there.

Gibberellic acid even runs counter in industrial hemp: 1000 mg per litre cut germination from 56 to 28 %. A compound ranking among the most effective in landraces does damage here. Nothing shows more plainly that the dormancy question cannot be answered without naming the material.

Cold stratification and what it actually does

Cold moist stratification at 4 Β°C showed no difference from the control after 30 days. The advantage appearing after 60 days is read as an effect of storage rather than the breaking of a rest period: the seed after-ripens slowly under those conditions, which has nothing to do with dormancy. As a targeted treatment it is of no use.

What remains open

Whether cannabis has a uniform form of dormancy at all is undecided. No study tests the same genotypes once for a hull barrier and once for a physiological block, and without one the split by origin can be described but not explained. In practice: with landraces and older material, potassium nitrate or chilling is worth a try; with fresh industrial hemp it is wasted time.

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