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‘Retipping’ Could Help Cultivators Grow More Cannabis in Smaller Spaces, Study Finds

By Alexander Beadle

Published: Jan 23, 2023   
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Retipping, a novel propagation method that helps cultivators grow more plants in less space, works just as well for cannabis as traditional micropropagation methods, a new study suggests.

Scientists from the University of Connecticut recently described a procedure for applying the retipping method to cannabis plants. Now, in a new study published in the journal HortScience, the researchers compared cannabis plants grown from traditional stem cuttings and micro-cuttings against those grown from retip cuttings (cuttings taken from new shoots on recently micro-propagated plants).

They found no significant differences in the cannabinoid content or the physical properties of the plants grown from each propagation method. The retip cuttings also successfully rooted without the use of a rooting hormone at the same rates as other methods did with hormone treatment.

Given this high rooting success and similarity to traditionally rooted plants, propagators should consider retipping as a means of expanding their liner production, the researchers say.

Retipping yields more high-quality plants in less space

For this new study, the UConn researchers looked at the ex vitro rooting success and growth of micro-cuttings, stem cuttings, and retip cuttings taken from two different strains of cannabis, ‘Abacus’ and ‘Wife’.

They saw that micro-cuttings of ‘Wife’ had an ex vitro rooting success of around 80% when harvested at or before the 12-week mark. This success rapidly fell off to 30% for cuttings taken at the 18-week mark. Rooting success for ‘Abacus’ plants ranged from 70% for 6-week-old cultures to 47% for 18-week-old ones.

In contrast, ‘Abacus’ and ‘Wife’ plants grown using the retipping method successfully rooted 76% and 81% of the time, respectively, and without the use of any rooting hormone. This is comparable to the rooting percentages seen in other methods that do use a rooting hormone, the researchers said.

Looking at the fully-grown plants, the researchers also saw no significant differences in total shoot length, number of shoots, or flower dry weight in the ‘Wife’ plants produced by each method. The ‘Abacus’ plants produced by retipping were slightly smaller and had less shoot length and flower dry weight than the other methods. But after an extra week of vegetative growth to reach the same size as the other plants, this normalized.

The researchers also found no significant differences in the cannabinoid content of plants grown from the three different propagation methods.

The main attraction of retipping is its ability to produce significant numbers of plants from a single mother plant and its cuttings. With this latest study demonstrating that the plants produced are equivalent to those produced by other methods, the researchers anticipate that retipping could become of significant interest to commercial operations.

“Retipping has the potential to produce nine-times as many plants in a similar amount of floor space as stem cuttings from traditional stock mother plants,” Jessica Lubell-Brand, a professor of horticulture at UConn’s College of Agriculture, Health and Natural Resources and principal investigator on the project, said in a statement. “This method could help cultivation facilities grow more in less space while maintaining the quality of their final product.”

How does retipping work?

In a world where cannabis and cannabis-derived products are increasingly in high demand, efficient cannabis cultivation practices are becoming ever more important.

One popular method of operation for cultivation facilities is to take stem cuttings from healthy ‘mother plants’ and plant these to make new, identical plants. However, this method requires significant amounts of floor space. Additionally, the mother plants can accumulate disease and lose vigor over time. Micropropagation – when small micro-cuttings are taken from another plant and cultured in vitro – is a solution to this problem of disease. But it also comes with problems of its own, such as the hyper-hydricity of shoots.

The retipping method for cannabis cultivation, as described in an earlier study from the UConn research team, relies on the fact that the micro-shoots growing from recently micro-propagated plants have a uniquely altered physiology, which helps them to root more easily ex vitro in mediums such as soil or rockwool. By repeatedly harvesting new shoots from these micro-propagated plants, cultivators can also produce significantly more healthy plants in smaller spaces.

“Not every cultivation facility has the means to build a laboratory and grow micropropagated plants,” Lubell-Brand said. “However, there are plant nurseries with laboratories that can step in to provide them, especially as more cannabis cultivation becomes legal in more states. This supply chain strategy is commonly used in the ornamental nursery trade.”

“The legal cannabis industry is forging ahead of the science,” added first author Lauren Kurtz, a doctoral student in the Department of Plant Science and Landscape Architecture at UConn. “Our lab is helping to bridge the gap and provide evidence-based strategies to improve cultivation.”


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