Reasons for dramatically lower THC?

R

rkmcdon

Well-Known Member
My last 2 harvests came in with dramatically lower thc levels. One cultivar that is typically 21% came back at 8% and another that is typically 20% came back at 6%. These were planted at the same time, harvested about a week apart. Harvest date was determined by trichrome inspection and the plants were harvested at the first signs of amber, so roughly 90% of the trichromes were cloudy.

They were grown under the same conditions as the previously harvests that yielded 21% and 20% thc's respectively with the exception of the soils. We are on a no-till soil that consists of:
20gallons sphagnum
20 gallons ewc
10 gallons pumice
7 gallons rice hulls
3 gallons biochar
8 cups basalt
8 cups azomite
8 cups gypsum
8 cups oyster shell
8 cups neem
8 cups kelp

The soil was allowed to cook for a month. This is the first harvest for these two cultivars in the current soil, but we've harvested other cultivars using this same soil composition and achieved thc's over 20%.
Other room parameters are unchanged: sealed room with co2 levels 1200-1500. Temp low to mid 70's degrees, humidity in the mid 40's, 1000w de hps lights about 4 feet above the scrog.
 
The Gram Reaper

The Gram Reaper

Well-Known Member
The only issue I can think of is the DEs harmed the bud and lowered the thc, but it doesn't look like you are too close now that I reread your post. If the double endeds negatively affected it, you would have been able to notice it while it was growing.

The buds would grow without hairs or showing much thc if it was the DEs fault. I let a plant get about 2-3 foot away from a DE and it started doing that on its top bud so now I backed off to 4 foot and the growth is doing fine like it never happened. If you have a lot of reflective material, you may have to back your DEs off a little.

Unless you went through a whole grow like this, or had other issues you didn't fix, I would say its your strain. You can't expect the same amount of thc between different phenos/strains just because the grow conditions are the same.

I had a killer strain I took in to get tested, I thought I won a pheno lottery it was so potent, it came back 12% thc. It was an absolute kick in the balls, turns out it was a lot high in other cannabinoids and CBD.
 
BobThe420Builder

BobThe420Builder

Well-Known Member
rkmcdon said:
This is the first harvest for these two cultivars in the current soil, but we've harvested other cultivars using this same soil composition and achieved thc's over 20%.
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This is your issue

To ASSUME a different strain would produce a similar THC, or effect, is just, well..... I'll be nice

Stupid

Just stupid


Using the same soil and etc to produce a different strain, is well, totally different, because it's a different strain

Strain depicts the THC, etc, not the medium and environment. Yes they can make or break a strain,but it's genetics that's is in charge here
 
MustangStudFarm

MustangStudFarm

Well-Known Member
rkmcdon said:
My last 2 harvests came in with dramatically lower thc levels. One cultivar that is typically 21% came back at 8% and another that is typically 20% came back at 6%. These were planted at the same time, harvested about a week apart. Harvest date was determined by trichrome inspection and the plants were harvested at the first signs of amber, so roughly 90% of the trichromes were cloudy.

They were grown under the same conditions as the previously harvests that yielded 21% and 20% thc's respectively with the exception of the soils. We are on a no-till soil that consists of:
20gallons sphagnum
20 gallons ewc
10 gallons pumice
7 gallons rice hulls
3 gallons biochar
8 cups basalt
8 cups azomite
8 cups gypsum
8 cups oyster shell
8 cups neem
8 cups kelp

The soil was allowed to cook for a month. This is the first harvest for these two cultivars in the current soil, but we've harvested other cultivars using this same soil composition and achieved thc's over 20%.
Other room parameters are unchanged: sealed room with co2 levels 1200-1500. Temp low to mid 70's degrees, humidity in the mid 40's, 1000w de hps lights about 4 feet above the scrog.
Click to expand...
Are you still going to get your soil tested?
 
R

rkmcdon

Well-Known Member
I think i did a poor job of explaining the situation, so let me try to clarify.

I have grown the two strains/pheno's in question before. The recent crops were clones from the same mothers. The previous time i grew these two strains we were using:
50% sphagnum
30% perlite
15% ewc's
5% Insect frass
We were then feeding with Age old bloom twice a week. Non feed days were just water with cal-mag
Both strains tested thc in the low 20's

This most recent crop, both strains were grown in the following soil mix:
20gallons sphagnum
20 gallons ewc
10 gallons pumice
7 gallons rice hulls
3 gallons biochar
8 cups basalt
8 cups azomite
8 cups gypsum
8 cups oyster shell
8 cups neem
8 cups kelp

We did not change other room parameters.
This crop tested 6% and 8% thc

I will be taking samples to a different lab for retesting.
 
R

rkmcdon

Well-Known Member
My current running theories are:

These two crops in question were planted at the same time. I wonder if i made a mistake when mixing the soil which created a problem
The current DE HPS are a year old. I've ordered new ones and will be replacing all of the bulbs
There is a chance its lab error, though i'm doubtful. I'll be having potencies checked at another lab just to see

I have wedding cake curing and it will go for testing next week. Hopefully i will see more typical results from it. If not, I'm leaning towards the lights being beyond their lifespan
 
R

rkmcdon

Well-Known Member
SupraSPL said:
The main thing I see wrong with that soil is, it critically depends on the quality of those castings.
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you know, i've always wondered about this. I have my own worm bin and hope to have my own castings starting in November. In the meantime, i found a place that sells worm castings by the yard and purchased from them. I honestly don't know how i would tell what quality they are.
 
H

halfbreed421

Well-Known Member
I think you are lacking in many of the micros you would be getting from the nutes you were using previously. From looking at your mix I think you'd be lacking magnesium and sulfur and probably other trace elements but idk whats in your castings. A month isn't a very long time either when it comes to microbes breaking down the things you added to your soil to make them available to the plant. Maybe you could add more diverse microbes to speed up the process? and humic acids to feed them
 
R

rkmcdon

Well-Known Member
Retested the two strains that came back at 6 and 8% using a different lab and they confirmed the low numbers were correct. Also tested my latest crop which came in at 17.6%thc and 5.2% terps so i don't think it was my lights. I did however replace all of the de hps in flower because they were all a year old and some a little over.

I honestly believe that something happened with the soil mix on the two crops that test so low, though i cant say exactly what it was. Hopefully it was a one (two) off and I won't have many more surprises like that moving forward

I'll be sending off soil samples in the next week of soil that's getting ready for no-till grow 2. I already have the soil savvy kit on hand and i've ordered the build a soil kit. I'm going to use both and see how they compare and which gives me more usable results
 
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