Increasing Weight and Cannabinoid Content Using Drought Stress

[valleymicro]

I have been reading this paper published in the School of Environmental Sciences regarding test results of controlled drought stress and impacts to THCA, CBDA, THC, and CBD.

Increasing Inflorescense Dry Weight and Cannabinoid Content in Medical Cannabis Using Controled Drought Stress

Using Controlled Drought Stress.pdf (262.9 KB)

Part of the Abstract:

Controlled application of drought can increase secondary metabolite concentrations in some essential oil-producing crops.

Summary of Trial:
In the trial, 14-day old vegetatively propagated rooted cuttings were transplanted and hand-fertigated using a nutrient mix described in the article.

15-days after transplanting, 8 plants were transferred into a larger walking growth chamber for flowering and transferred into 11L pots.

10-days into flower and all the plants were fertigated at the same rate.

39-days into flower and plants were randomly assigned drought or control (non-drought) treatment groups - with 4 plants in each group.

The control group was irrigated without any change.
The drought group was not fertigated until the plant water potential (WP) reached between -1.4 and -1.5 MPa (drought stress threshold). This occurred after 11 days without fertigation.

Conclusion:

This study suggested that controlled drought stress can increase the concentration of the major cannabinoids (THCA and CBDA and the rield of THCA, CBDA, THC, and CBD in chemovar II cannabis without reducing inflorescence dry weight and irrespective of decreased Pn.

These results were achieved by gradually drying the substrate over 11 days until plant WP reached approximately -1.5 MPa during week 7 in the flowering stage.

I also compiled the listed of tools used for this trial:

• Stem Psychrometers and Data Loggers
  http://au.ictinternational.com/products/psy1/psy1-stem-psychrometer/
• Substrate Moisture Sensor
  https://www.metergroup.com/environment/products/ec-5-soil-moisture-sensor/
• Leaf Net Photosynthesis Measurement System
  https://www.licor.com/env/products/photosynthesis/

This is my attempt at a high-level explanation. I’m sure I might have missed some key points. I attached the article for everyone to read.

[Bob13]

Interesting, got to watch many other factors to make this work. Gonna look through your links now

[Northern_Loki]

This is interesting, there has been a bit a anecdotal evidence on this over the years. Good to have a controlled study.

FWIW, the photosynQ is probably a less expensive option to the the Licor Leaf Net Photosynthesis Measurement System.

[anon32470837]

Nice study. It certainly re-inforces the common wisdom of “Dont over water”

Seems to me, the least expensive way to implement this is just buy a bottle of LITFA

[valleymicro]

What I forgot to mention was the measured differences between the drought and control groups.

Drought-stressed plants had:

• Increased concentrations of THCA and CBDA by 12% and 13% respectively.
• Yield per unit growing area of THCA was 43% higher
• CBDA yield was 47% higher
• THC yield was 50% higher
• CBD yield was 67% higher

[valleymicro]

LITFA and the KISS method will get you far.

[Northern_Loki]

My inherent laziness has allowed me to replicate similar drought conditions each year.

As a point of comparison, I’ve found that hot peppers do not get “hot” without some induced drought/heat stress.

[50State]

I remember watching a GHS video years ago where Franco said to let your plants really dry out weeks 2 and 6 of bloom for better yields and cannabinoid production.

[Papalag]

I remember that same conversation my friend he made a point by lifting up the pot in the video I watched weeks 2&6

[Cannasaurusrex]

From what I read, the drought condition was only applied once during week 7. Seems like something we can actually use, how many weeks before proven harvest window, would be beneficial? Obviously after 11 days in my containers, the plants would be basically a wilted pile of shit. But aside from genetics media, etc.it would be nice to know how often to let roots completely dry using the moisture levels in the study. More reading…fuck…just don’t like starving plants, or feeding ferts to them, personally. LST and plant mutilation (My pruning tech lol) is proven, it would be nice for the stientists to quantify the wet/dry cycle we (soil?) growers use. I knew hand-watering is cheaper than blu-mats…better too? LOL Can’t imagine using this in hydro??? turn off pumps for 11 days??? With that ‘measured THC increase’ this drought thing will revolutionize cannabis growing forever…or sell a shit ton of metergroups moisture sensor?

[Northern_Loki]

@Cannasaurusrex

Can’t imagine using this in hydro???

I was wondering this too. Possibly encouraging stress response using some other mechanisms, UV, chitosan, hedione?

[50State]

You wouldn’t turn the pumps off for 11 days you’d have to maintain or replicate the moisture levels in the medium dropping over 11 days to a low WP of 1.4 to 1.5. They didn’t water for 11 days because it was in soil and the levels slowly reached this level. I don’t know what a WP of 1.4 to 1.5 would even being to mean but if their soil took 11 days to dry out its made of good stuff my plants would be dead after 5 days.

[DiggySoze]

I’m wondering what factors influenced their decision to start the test at the time they did.
With a total flower time of 54 days, did the drought-stressed plants finish early?
If the control plants had gone an extra week or two, would they have finished at similar cannabinoid levels?

[orange]

Exactly @DiggySoze. They dont talk bout the normal ripening of their tested cultivar so it may be forced ripening as the action mechanism. Thats an easy attack on the methods if they normally run 10wks+ on that cultivar.

Also in organics u do NOT want the soil 2 dry out. Look at SIPs n the success they have. Id much rather overwater a lil than underwater n lose growth.

Lastly its obviously cultivar-specific. Unlike supermarket produce yer cannabis aint that highly hybridized not even close.

[DiggySoze]

@orange

Also in organics u do NOT want the soil 2 dry out. Look at SIPs n the success they have.

I stray from the generally accepted organic watering schedule, and let them dry out more than most. If you’ve seen the Kashmir’s I’ve got in flower right now, all the leaf tips are burned because of exactly that, letting the soil dry out a little too long and soil life dying out and solubilizing.

[orange]

Yup thats what I try to avoid by keepin em moist.

Drought tolerance is cultivar-specific down to the specific plant n terroir.

[DiggySoze]

@orange That’s just leaves tho. Took this pic this morning at twilight. Have you heard of the old Italian tomato farmers flooding their fields with saltwater prior to harvest?

[orange]

Heard lotsa anecdotes but dont mean theys generalizable. Ppl grow great plants w shit methods n ppl grow shit plants w great methods.

Like us pot farmers today - farmers of everything 4ever have had their tips n tricks n theys all different round the world. Do what works but dont assume its prescriptive.

Grape vines grown on one farm in France grow & taste different from the same cloned vines grown 1 hill over.

I figure do what works for u but dont preach until u get such highly hibridized like sweet corn errr roma tomato errr broccoli in the supermarket.

[DiggySoze]

@orange

Heard lotsa anecdotes but dont mean theys generalizable.

What anecdotes? They provided hard data. There’s variables that need to be accounted for, but it does prove validity, if even only under specific circumstances

[vernal]

@orange

Grape vines grown on one farm in France grow & taste different from the same cloned vines grown 1 hill over.

That’s just in people’s heads.