Collected Q&A from Readers’ Emails, Part 7

72 Hours of Darkness?

1. I heard from a very renowned Cannabis breeder that 72 hours of complete darkness before harvesting does wonders to plants. I have indeed tried it several times and it does change the taste completely… for the better! Why is this and what’s happening during those 72 hours?

As we all know, plants are dependent on light to conduct photosynthesis, which produces sugar, which in turn feeds the plant and allows it to live. But, to answer this question, let’s catalogue what can occur inside a plant in the dark:

• There is a subset of chemical reactions that occurs during photosynthesis called the dark reactions. In fact, they are also ultimately dependent on light (because five of the enzymes used in the dark reactions depend on light), but they can be carried out, or finished, in the dark (these reactions are also known as the Calvin Cycle). It is these dark reactions that produce carbohydrates (sugars). Think of these dark reactions as the terminal phase of photosynthesis. Those reactions can occur in the dark, but only for a short period before the light-dependent components of the reactions run out and photosynthesis shuts down.

• Mitochondrial respiration continues in the dark, but this is merely the release of carbon dioxide.

• The plant detects the absence of light, which it uses to set its circadian clock so that it “knows” when to flower.

In short, without light, most meaningful plant metabolism shuts down. There is a chance that something involving the plant’s circadian rhythm mechanism is changing its production of certain volatile compounds (think essential oils). This has been noted in the favorite test plant of botanists, Arabidopsis,1 but I am sure it has never been studied in Cannabis and I think it is a long shot.

Instead, I believe that what you are experiencing is a placebo or “nocebo” (since you are depriving rather than adding something) effect. I realize that this can be hard to accept, but I do not see any scientific basis for why this could be occurring.

Questions like yours are what fascinate me about Cannabis husbandry. There is a lot of myth associated with this plant and without controlled experiments we are left to conjecture. I would love to be wrong about your observation, and with decriminalization occurring, I believe we are on the cusp of sorting out what is lore from what is fact.

Science aside, I see no harm in the practice and no reason why you should stop if you firmly believe it is making a difference. Crazier things have been discovered!

Storing Cannabis

2. In reference to curing Cannabis; if stored properly, once cured, will Cannabis remain fresh indefinitely? Meaning, does it ever go stale?

Like everything else, even Cannabis will eventually go off. The enemies are oxygen and light. (Light is worse because when light blasts your pot, you don’t even get the degradation from THC to CBD that oxygen leaves you with; instead, you get nothing!)

We live in an oxygen-rich environment, and that chemical takes its toll on everything it touches. The best you can do is slow its dastardly work down. Properly cured and stored (dry, dark, tightly packed, cool), Cannabis will remain fresh for a very long time — years, even. But, even stored properly, there will be a gradual degradation.2

Reflective Materials vs Paint

3. I have a friend who has his grow room walls lined with a reflective material (like inside a grow tent). Is there any benefit to doing this? I always thought white walls, ceiling and floor was appropriate.

When I began growing I used mylar unquestioningly. I thought it was obviously more reflective because I could see objects reflected in it. Then one day, after about the one-thousandth time the stuff tore or fell off the wall, I realized how unbearably noisy it was, rattling every time the fan rotated past it. I tore the stuff down, painted the walls flat white and haven’t looked back since. I hate the stuff.

As it turns out, white paint and mylar offer about the same reflectivity (~92-98% for the mylar, ~90-95% for the paint). And the few-percentage point difference is more than made up for by the fact that white paint doesn’t flap loudly in the wind, doesn’t tear or require adhesives to stick to the wall, and simply adding another coat easily cleans up the walls (which get dirty fast). If you do decide that you absolutely must have the mylar, be careful as it does conduct electricity, a safety hazard (and yet another argument for the paint.) Applying it with a spray adhesive is your best bet.

Which white paint? Behr Ultra Pure White is about as good as it gets at around 94% reflectivity, however, any white paint (I’m a cheap bastard when it comes to the grow room) will do the job. Flat paint hides wall imperfections while high-gloss exaggerates them–in case you are inviting guests over to look at your walls.

Author’s Note: These questions originally appeared in my column in the January issue of Sativa Magazine.

Sources/for further reading:

1. Goodspeed, D., Chehab, E. W., Min-Venditti, A., Braam, J., & Covington, M. F. (2012). Arabidopsis synchronizes jasmonate-mediated defense with insect circadian behavior. Proc Natl Acad Sci U S A, 109(12), 4674-4677. doi:10.1073/pnas.1116368109

Fairbairn, J. W., Liebmann, J. A., & Rowan, M. G. (1976). The stability of cannabis and its preparations on storage. J Pharm Pharmacol, 28(1), 1-7. Retrieved from