Higher propagation

New research exposes a cannabis breeding technique that could allow cultivators to grow nine times more plants


Mother plants are a staple in most commercial cannabis operations. Shoots from a mother plant are cut and their severed ends are dipped in cloning solution to become vegetative cuttings — new cannabis plants. The mothers are cloned repeatedly like this for several months before another mother plant replaces them.

This is how cultivators ensure the quality of their bud is high, but also that it’s standardized. They’re essentially growing the same plant over and over again. In technical terms, you’d call it a monoculture of the same cultivar. 

But there are problems with cloning like this. Sometimes plants require a rooting solution to stimulate growth. Mother plants take up a lot of space and they lose vigor over time. And if you take too many clones from a single mother, you can end up with unhealthy liners (aka young plants).  

“There’s a lot of potential for disease,” Lauren Kurtz says.“They’re constantly wounding the plants.”

Kurtz is a graduate student in horticulture at the University of Connecticut (UCONN). She recently co-authored a research paper with Jessica Lubell-Brand comparing the growth efficiency of regular vegetative cuttings against two other types of liners: microcuttings and re-tip cuttings. 

Their findings suggest there may be a better way to commercially propagate cannabis mother plants. 

“The industry is mostly clonally propagated,” Kurtz says. “We’re just using basic plant propagation strategies that have been used with other plants and [applying them] to cannabis.”

The researchers planted tissue culture from each of the three types of liners and grew them in identical conditions. They then measured different growth parameters between the three treatments. 

They found all three methods produced plants that grow to the same end size. Kurtz says they were expecting a clear winner, but there wasn’t one. Vegetative cuttings, micro-cuttings and re-tip cuttings all produced mature plants with similar sizes and flower yields. 

However, the re-tipping method stood out in one significant way. Instead of traditional propagation, those mother plants were micropropagated and grown in small containers in a laboratory under sterile conditions. The re-tip cuttings were then harvested from those and grown into full cannabis plants. Re-tipping in this way could allow cultivators to increase output by using the plants as mothers in addition to using them as production plants. 

And re-tip cuttings take up far less space than conventional vegetative cuttings.

“Re-tipping 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,” says Lubell-Brand. “This method could help cultivation facilities grow more in less space while maintaining the quality of their product.”

Kurtz says the re-tip cuttings grow vigorously and are less susceptible to developing diseases over time. They also don’t require a rooting solution.

But adopting re-tipping would require cannabis grow operations to invest in a whole new system of plant propagation. 

“Tissue culture laboratories are necessary to produce micropropagated plants. So you need a sterile environment, you need an autoclave, you need a laminar flow flood,” Kurtz explains. 

Lubell-Brand also offers a possible workaround. 

“Not every cultivation facility has the means to build a laboratory and grow micropropagated plants,” she says. “However, there are plant nurseries with laboratories that can step in to provide them, especially as cannabis cultivation becomes legal in more states.”

The goal of this research, Katz says, is about exposing this propagation method as a potential for cannabis companies

“The legal cannabis industry is forging ahead of the science,” Kurtz says. “Our lab is helping to bridge the gap and provide evidence-based strategies to improve cultivation.” 

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