increased yield but reduced potency

It seems I have a dilemma.

Thru excellent conditions, I have increased my yield to 1kg/1000w. Heavy water and ferts in addition to CO2 are the big factors. Yet, my friends tell me my potency and taste have gone down. The same clones grown in 2 different locations, mine while it looks big, oily and delicious will have a reduced potency by a significant factor over another grow room. My plants looks excellent without fert burn and the buds are very oily vs other growroom but lacks the kick.

Im considering reducing my CO2 to 700ppm and cutting back on the ferts and water by 20% to see if that makes a difference. I know my yield is going to go down significantly and my hope is that the potency will be back in return.

Anyone have any suggestions or experiences they wanna share?

Just a few questions...

How are you doing the harvest? I'm talking about any dark period prior, the drying, and the curing. How long it is done for and the environment.

What nutrient system are you on?

What kind of lighting are you using? Wattage and bulb brand and model.

From what I know about cannabinoid production there are a few contributing factors. Nature and nurture. The Nature part is compensated for as you claim your clones in other gardens are more potent. So it has got to be a nurture part.

I have learned that cannabinoids are a defense mechanism of the plant designed to protect the seeds from harmful UV rays. Some growers utilize UV, or at least far blue light, to try and boost the production of these chemicals. Another method I've heard of is using a pin or tack through the stem like a piercing during the last week of life. The stress reaction supposedly causes the plant to focus on the production of trichomes.

As far as the rest goes I cannot really delve too far into the chemistry. There are a few books I can suggest that might shine more light into your process and how you can improve it.

"The Total Synthesis of Cannabinoids" by Raj K. Razdan
"Marijuana Chemistry - Genetics, Processing, & Potency" by Michael Starks

Are you harvesting on a schedule or by checking for ripeness?

im checking for ripeness with my scope.

Just to make it clear, my potency has been reduced with the addition of CO2 and the heavy usage of feed water that goes along with the increased growth. Nothing has changed except the elimination of air circulation because Ive started using CO2. Im a very experienced soil grower but trying to go to hydro because its cleaner and higher yield. Its true that its a more accurate system, cleaner to run and much, much higher yielding per watt and the product looks much better. But i really wasnt expecting a reduction in potency, infact I was kinda expecting higher.

My hypothesis is that while Im getting bigger buds, the potency isnt keeping up with the biomass production. The tric's are there but the potency isnt. There is a theory out there called 'nutrient dense foods'. In essence, plants grown in proper soil, biological activity and environmental conditions yield a more delicious, nutrient rich product such as an outta this world tomato. As opposed to a cardboard tasting, gassed hydroponic tomato that you buy at the local supermarket during the off season. I am wondering if this is the effect that Im seeing. I know this is true for fruits, veggies and grains but for THC? Tho I guess I shouldnt be surprised...

Try cutting back the CO2 the last week or 2.....If you're growing your trees bigger, you might want to let them go longer to finish. But your potency shouldn't be reduced that much

I missed another item earlier.

H2O2 was added to the regiment and while its done a magnificent job of keeping the whole system clean and roots white, I think its also contributing to the lack of taste.

OZUT said:

Try cutting back the CO2 the last week or 2.

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Ive read this before and was the impetus for me writing the question on here.
I grow continuous so its makes it difficult to cut back. Does anyone have a solid number for what the CO2 ppm should be at for the last few weeks?

Excellent topic!! I balance my spectrum with 1/2 MH x 1/2 HPS. I believe that staggering the lights and shuffling the plants ahead to the next light every week or two gives you a really happy medium of potent, sticky weed and a not as big but plenty enough harvest. I got exactly a LB per 1000 on my last grow, extremely potent.

i read in a high times mag awhile bak that high co2 in the last 3 to 4 weeks can block certain terpentines and flavor. it recommends 450 to 550ppm which is just a lil higher than normal non-enriched outside air

Snow Crash said:

"The Total Synthesis of Cannabinoids" by Raj K. Razdan
"Marijuana Chemistry - Genetics, Processing, & Potency" by Michael Starks

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Thanks Snow Crash.

The Raj book is a biochemical pathway reference and really not much use.
The book by Michael Starks looks alot more beneficial and Im in the process of reading it. Thanks for the references.

ecofrog said:

the heavy usage of feed water that goes along with the increased growth.

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As I am sure you know water does not just get used up by or consumed by plants and then remain in the plants or just vanish. Much ends up in the air of your grow room through transpiration. Has your humidity level increased along with your increased use of water?

Brick Top said:

As I am sure you know

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I have degrees in biology and chemistry with 20 years of job history in both so ya, I know.

water does not just get used up by or consumed by plants and then remain in the plants or just vanish. Much ends up in the air of your grow room through transpiration. Has your humidity level increased along with your increased use of water?

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Yes I noticed the humidity level jump as did the water usage when I moved to CO2 and hydroponic conditions but still fully under control. My humidity level is ~42% at the end of the day and starts at ~36% in the morning. I had to put on a 2nd de-humidifier but both run on low. As an aside, Danby de-humidifiers are the best workhorse for the money.

Im curious what do you think the humidity has to do with the taste or potency?

It doesnt taste like chemicals or salty over fert'ed medicine, more like a bland version of its once delicious self. And this isnt just one strain but has been noticed throughout the grow room. I think normally it wouldnt be noticed but that I have other growers or 'controls' for the strains to compare.

I am a little confused, is the "other" garden soil and yours is (now) hydro?
The lack of taste is a common complaint for hydro grown meds takes a lot of learning to get the taste out of hydro. There is a product or 2 that are supposed to help, but i believe they are just fake flavoring, not actually a replacement of turpenes that are missing in hydro.
Now the potency is something i have never heard of, in fact always the opposite. Is it possible to throw a couple soil plants into the room to do a side by side comparison so see if it is environmental or actually the hydro? Also i do not use any h2o2 in my system at any time, instead i use Dutch Master Zone, seems to work great with no side effects, if you are looking to rule out the h2o2.

Your friends are just used to your weed now.

ecofrog said:

Im curious what do you think the humidity has to do with the taste or potency?

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My initial thoughts about humidity were not actually about taste but only potency but after thinking about it I guess it could be connected to both, if humidity would be too high.

When grown in conditions of higher humidity plants produce less resin and what resin is there is less likely to contain as much THC. It would also likely mean fewer cannabinoids overall and fewer terpenoinds and fewer flavonoids and fewer alkanes and fewer esters all those things added together would cause a flavor change along with a potency change.

The other part of humidity is it causes trichome stalks to grow taller and thinner and buds will look very frosty but because of the taller thinner trichome stalks the trichome heads are far more apt to be knocked off when handled during harvesting and trimming and hanging and being put into jars for curing and taken out of jars after curing and then when packaged for sale, again all adding up to less potency when smoked due to the number of lost trichome heads.

When the CO2 level goes over 2000 ppm plant growth will slow down because the concentration of CO2 is too high, but I did not see that you had levels that high.

In order to maximize yield and minimize the length of time till harvest, some growers increase the amount of CO2 to the grow area so the plants have a steady concentration of about 600-1500 ppm when the light is on.

The optimal amount of CO2 will depend on the amount of light available and the temperature of the air that surrounds the leaves. As the amount of light and temperature increase, the plant is able to process more CO2. This results in a quicker growth rate.


Here are some CO2 levels and how they affect plant growth.

Below 200 ppm (Plant Growth Slows)
350-430 ppm (Outdoor Air)
600-1500 ppm (Optimal For Marijuana)
Above 2000 ppm (Toxic For Marijuana)

TruenoAE86coupe said:

I am a little confused, is the "other" garden soil and yours is (now) hydro?

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yes that is correct. I went from soil to hydro.

I planned on doing a side by side soil grow in a few months. Thanks for the input.

Brick Top said:

When the CO2 level goes over 2000 ppm plant growth will slow down because the concentration of CO2 is too high, but I did not see that you had levels that high.

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My CO2 is set at 1250ppm and cycles between 1200 to 1350.

ecofrog said:

yes that is correct. I went from soil to hydro.

I planned on doing a side by side soil grow in a few months. Thanks for the input.

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There is your answer. Hydro is known for bland tastes, compared to organic even more so.

You mentioned that you switched growing mediums so I'm assuming you switched nutes, from what to what?

read that hydro weed is suppposed to be less pottent , like shorter highs and what not