How much water does cannabis really need?

About your recent column: Does it really take six gallons of water per day to grow a cannabis plant?

—Dro Savoire

Right? I also feel like that number is a little high, so I did some more research. Here is what I found: According to these folks (www.theganjier.com/2015/07/02/
how-much-water-does-one-marijuana-plant-need-to-grow), a cannabis plant needs one gallon of water per day per useable pound of cannabis created. So a plant that yields 6 pounds would in fact need six gallons per day, while a plant that yields 2 pounds would only need two gallons per day. Most indoor plants yield way less than 6 pounds after harvest (if you can get more than 6 ounces from a decent sized indoor plant, you are a pretty good gardener), and outdoor noncommercial gardens will usually give you two to four pounds per plant. So while the “six gallons of water per day” may be accurate if everyone is growing monster plants, it doesn’t tell the whole story. Also consider that a bottle of wine may run you 400 gallons of water, while an eighth of an ounce of quality cannabis will cost about 1.9 gallons of water. Which one looks like a better deal for a drought-conscious state? Maybe we should start some sort of “Save water, grow weed instead of wine” campaign?

The Oregonian just reported that more than half of 150 concentrates tested for pesticides came back positive. However, there is nothing restricting pesticide-laden concentrate from entering the retail market. Many pesticides that were found are known carcinogens. The full story is here: www.oregonlive.com/marijuana-legalization/pesticides. Can you respond to this in a column? Are you aware of any similar study done with products sold in California dispensaries? Is there any person or group advocating for stricter regulation of pesticides in cannabis cultivation? Thank you.

—M. Gibb

Good question. No one wants to inhale a bunch of pesticides along with their delicious marijuana. Way back in April 2015, the California State Water Board released a brochure containing some guidelines for responsible pesticide use around cannabis plants (http://blog.sfgate.com/smellthetruth/2015/04/08/marijuana-pesticide-guidelines-issued-by-state-of-california). The thing is, there hasn’t been a ton of research about which pesticides are best for cannabis growers. The best practice would be for growers to use OMRI certified organic and natural pesticides, but not everyone does that. Testing facilities generally look for pesticide levels that are above generally accepted tolerances, and most clubs these days won’t accept cannabis that hasn’t been tested. I would say that most of the cannabis found in the California clubs is as clean as possible, but your best bet may be to find a grower or a club that specializes in organically grown medicine. I hope that helps.