Introduction to Seed Scarification
Seed Scarification in botany refers to the intentional alteration, weakening or opening of the seed coat in order to aid or improve the germination process. Methods typically include abrasion, seed coat rupture, and chemical alteration. Scarification is a vital and sometimes necessary tool used in many commercial agriculture applications. The efficacy of scarification on cannabis seeds is often debated and widely overlooked. Cannabis, compared to many other species of plants, is normally effortless to germinate. However, certain seeds or cultivars can be particularly difficult to germinate. Reduced germination rates are normally attributed to the age of the seeds, poor storage and handling, improper curing, and genetics.
When to Scarify: Ideally, cannabis seeds should germinate within 24 hours at 80° F. Warmer incubation temperatures will decrease the germination time but increase the pathogen risk to the seeds and sprouts. Seeds that take longer than 72 hours to germinate quickly develop increased risk for pathogen infection, this is especially true if the temperatures are higher than 70° F. The general rule of thumb is that all seeds that do not germinate within 72 hours should be scarified. It is important to note that scarification can be completed before or during the germination process.
How to Scarify: For cannabis seeds the two common methods of scarification include abrasion and seed coat rupture or cracking. Abrasion is normally performed by rubbing or tumbling the seeds with sandpaper or gently scraping the seed coat with a sharp edge. Abrasion is a less intrusive method but far less effective than the rupture method. The rupture method involves penetrating the shell completely but gently. If you observe a cannabis seed closely you will notice a seam that forms a line of symmetry, in botany this seam is referred to as the “raphe”. The raphe is where the seed normally splits during germination and the goal of rupture scarification is to manually crack the seed along this seam (Figs.1A, 1B). It is very important to note that seed coat rupture should always be implemented with a tool that is designed to limit the amount of force applied to the seed in order to protect the delicate embryo inside. Manually cracking the seed assists in germination by exposing the embryo to moisture and minimizing the energy required for the embryo to emerge from the seed coat and therefore improving the overall viability of the seeds.
Seed Scarification Investigation:
Below are the results of our recent investigation.
Abstract: 200 cannabis seeds originating from a single host plant were evenly divided into 2 groups of 100. 100 of the seeds were scarified with a seed cracking tool produced by Twenty20 Mendocino and 100 seeds were left untouched. The results of the study indicate that scarified seeds have a 21% higher chance of survival and a 2-fold increase in germination after 120 hours.
Seed Scarification Method:
200 seeds were gathered from a single female plant. The seeds that were used for the experiment originated from an autoflower variety that had previously exhibited lower than average germination rates. The seeds were randomly separated into 2 equal batches of 100 seeds each, Group “A” and Group “B”. 100 seeds from group (A) were ruptured using the Twenty20 seed cracking device (Fig. 3). Group (B) seeds were left untouched. Each group of seeds were folded into a damp paper towel and placed in a temperature controlled environment that remained between 80° F and 82° F. Observations were documented daily over the next 180 hours. We defined “germinated” as any seed with a tap root extending from the seed coat by more than 1mm.
The graphs below (Fig. 2) depict the results of the experiment. After 30 hours, the first observations were documented. 17% of the scarified seeds in Group “A” had germinated and 0% of the non-scarified seeds (Group “B”) had germinated. Group (B) first exhibited signs of germination at 54 hours with a rate of 1% (Fig 4), while 31% of the scarified seeds had germinated within the same time frame. The rate of germination in both Group “A” and Group “B” remained linear for the subsequent 90 hours until Group “A” reached a peak of 99% at 120 hours and Group “B” plateaued at 80% at 144 hours.