In commercial cannabis cultivations, growers do not usually start from seeds for a variety of reasons: uncertainty regarding genetic stability, and equal uncertainty regarding the germination rate and the eventual sex of the plant. Therefore, it has become common practice to propagate cannabis through cloning, with cuttings taken from a mother plant. Another procedure that is used to increase the productivity of cannabis plants is topping or fimming, which triggers the production of axillary shoots that increase the number of flowers. This procedure is usually carried out on the cuttings. Yet, since these are still young plants and have not particularly strong roots, it takes up to 10 days for the plantlet to fully recover from the stress. In a recent paper by Sylvain Gaudreau, Tagnon Missihoun & Hugo Germain, they explore early topping, which is the carrying out of fimming on the mother plant before cuttings are taken, thus shortening the plantlet cycle by 7-10 days.
As the authors explains, “Topping or fimming consists of the removal or destruction of the apical meristem, which will trigger the production of axillary shoots.” This increase the number of flowers per plant, thus ultimately improving the yield. “Topping or fimming is generally performed after the cuttings have been transferred to rooting media for two weeks,” they explain.
The science behind this is not fully certain, yet. But the authors say that “when the apex is damaged, the plant enters a survival mode by breaking the dormancy of the axillary inflorescences and start to develop, resulting in a plant with several side branches that will each produce flowers.”
By carrying this procedure out on the mother plant, the authors have observed a shorter plant cycle: “Since the mother plant has a well-established root and aerial system, it promptly launches the development of axillary shoots, which emerge rapidly since the plant can draw nutrients from the media and perform photosynthesis efficiently.” By taking these kinds of cuttings then, the plantlets won’t have to undergo the premature stress of topping, and will already present the improved branching that such a procedure ensures. “We have produced hundreds of plants using this modified procedure and in all cases the production time was faster with early toping compared to the standard topping in all the cannabis varieties tested,” the authors point out.
Yet, the authors remark that they had very positive results on the 8 cultivars that they tested, and therefore it is still not fully clear how early topping might affect different genetics. “It is unclear how well this approach will work with other genotypes of cannabis, thus we recommend that growers first test the performance of this method on their genotypes in a pilot trial. Due to the space, time and plant number constraints faced by cannabis growers, this new cultivation method can represent a more profitable approach to plant propagation,” they conclude.