A little water deprivation — or "drought stress" — appears to even improve potency.
"We found an increase in cannabinoid concentration, and especially cannabinoid yield," he said.
According to Caplan, cannabis plants in nature respond strongly to light. But more light isn't necessarily better, particularly when you want to maximize the production of the flowers that contain active chemical ingredients like THC, cannabidiol and other cannabinoids.
Tip #3: Any old dirt won't do
"Having three leaves compared to two leaves had the same rates of rooting success, but had a higher quality roots," he said.
According to Caplan, it's critical to have good soil drainage for the flowering stage.
You might worry that cutting back on the water would limit your plant's growth. But Caplan found that a little water stress during the flowering stage doesn't affect the amount of flowers you harvest.
Tip #2: Too much fertilizer makes for feeble flowers
Illegal producers' homegrown wisdom doesn't always stand up to scientific scrutiny, Caplan told Quirks & Quarks.
The practical details of implementing legalization have largely been left to the provinces and territories, so residents of Manitoba and Quebec, for example, will not be allowed to grow plants at home.
For years, the popular image of cannabis growers has been scruffy hippies getting high on their own supply in a disorganized underground economy, rather than shiny white industrial agriculture facilities. Even larger-scale operations involved minimal quality control or lacked formal record keeping.
A student inspects a cannabis plant at Niagara College Canada’s teaching laboratory in Niagara-on-the-Lake, Canada. Credit: Niagara College
In Canada, government regulations require producers to use an independent lab to measure the level of cannabinoid in dried cannabis flowers and oils so that the resulting products can be labelled appropriately. Producers must also test for contaminants such as the bacterium Escherichia coli, mould, heavy metals and 96 types of pesticide. When edible cannabis products become legal in Canada later this year, they will face similarly stringent rules, says Purcell; labels on such products will have to convey the same nutritional information as do those on any other food product. In the United States, the regulations are broadly similar to those in Canada. But each US state where medical or recreational cannabis is legal sets its own testing regime — and those requirements can vary widely and change quickly. “In Delaware, the regulations are now totally different than two years ago,” says Marcu.