Underperforming plants, various strains

Fairly new to soilless but long time grower. Currently in a sealed room, 74 degrees, 1000 PPFD, 850 ppm CO2, 50% RH.

Some strains (AK47, Purple Punch, Gelato and a few others) do fine.
Other strains (Blueberry Cookies, and now Zkittlez) produce almost no trichomes.

I'm using Pro-Mix HPCC adjusted at transplant to flower to 6.2 PH, feeding with Pure Blend Pro Bloom at 20ml per gallon PHed to 6.8 which puts the final run off at 6.5-6.6

Plants look healthy, good vegetative growth, just no trichomes and the pistils seems to start turning early.

Any idea what might cause this with some strains and not others? For contrast most of my experience is hydro and pretty much every strain did well as long as the roots stayed clean.

Thinking back, the first plant this happened with was GSC. I use tap water but ppm is low at 70. I'm wondering if some strains are more sensitive to cal-mag deficiencies. It's something to try.

I asked my AI buddy. Here is his response:

1. Nutrient Imbalance or Deficiency

• Potassium (K):
  • Trichome production and resin synthesis rely heavily on potassium during flowering. While Pure Blend Pro Bloom is a quality nutrient, it may not supply enough potassium for some strains, particularly resin-heavy ones like Blueberry Cookies and Zkittlez.
  • Solution: Supplement with a PK booster or potassium sulfate to ensure adequate levels during mid-to-late flowering.
• Micronutrients:
  • Strains that are poor trichome producers may have higher demands for micronutrients like magnesium or sulfur, which are crucial for terpene and resin production.
  • Solution: Consider adding a Cal-Mag supplement (even in soilless), as coco coir in Pro-Mix HPCC can bind calcium and magnesium.

2. pH Discrepancies

• While your runoff pH of 6.5–6.6 is within an acceptable range, soilless mediumstypically benefit from a slightly lower pH (5.8–6.2) to optimize nutrient uptake. Some strains might be more sensitive to pH at the root zone.
  • Solution: Adjust feeding pH to 6.2 to match the medium's ideal range, which may improve nutrient availability and overall trichome production.

3. Environmental Factors

• Humidity Levels:
  • 50% RH is good, but resin-heavy strains often thrive with slightly lower RH (e.g., 40–45%) in mid-to-late flowering. Higher humidity can inhibit resin and trichome production as the plant focuses on moisture retention rather than defense mechanisms like trichome production.
  • Solution: Gradually lower humidity during the second half of flowering to encourage resin synthesis.
• Light Intensity:
  • 1000 PPFD is excellent for most strains, but some can respond negatively if the light intensity is too high, especially if the spectrum lacks UV or blue light, which help trigger trichome production as part of the plant’s stress response.
  • Solution: Introduce supplemental UV or full-spectrum lights with UV-A and blue light during flowering to promote trichome formation.

4. Genetic Variability

• Some strains are naturally less trichome-dense than others due to genetics. Blueberry Cookies and Zkittlez may be less resinous compared to strains like Gelato or Purple Punch in your environment.
  • Solution: Focus on optimizing environmental stressors (e.g., light, humidity, and temperature dips) to push these strains toward higher resin production.

5. Pistil Browning and Premature Aging

• Possible Causes:
  • Nutrient Burn or Imbalance: Overfeeding (even without visible signs of toxicity) can cause pistils to age prematurely.
  • Environmental Stress: Elevated temperatures, light intensity, or high CO2 levels without matching nutrient or humidity adjustments can accelerate the flowering process.
  • Genetics: Some strains have shorter flowering windows and naturally brown earlier.
  • Solution: Reassess feeding strength (consider lowering ppm slightly for sensitive strains) and closely monitor environmental factors for stress points.

Next Steps

1. Adjust your feeding pH to 6.2 and monitor runoff for better nutrient uptake in the Pro-Mix HPCC.
2. Lower RH to 40–45% during mid-to-late flower to enhance trichome production.
3. Introduce a PK booster or supplement potassium and magnesium to support resin synthesis.
4. Experiment with UV-A or blue light supplementation during late flowering for trichome stimulation.
5. Consider genetic variability and prioritize strains with proven performance in your environment for future cycles.

Clones or from seed?

It could just be bad luck. Ive certainly seen my fair share of monstrously big plants that have basically no trichomes.

Of all these:

- cal-mag seems to be an obvious upgrade.
- I can try lowering the feed PH to 6.6-6.7 but 6.2 would lower the in medium PH too much I suspect.

Might directly address the issue.

These might be overall helpful but I don't suspect they go to the root of the problem:

-I can add a PK booster in mid/late flower - my feed ppm is on the low side to begin with.
-UV in late flower

Farmer's Hat said:

Clones or from seed?

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All clones.

Farmer's Hat said:

It could just be bad luck. Ive certainly seen my fair share of monstrously big plants that have basically no trichomes.

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I've wondered that too, seed variability or something. The Blueberry Cookies I tried with two different seeds/moms, same results. The Zkittlez just one seed so far. I didn't mention but the first time it happened was with GSC, not as bad as the other two but same gist, low trichomes and bushy buds. I'm hitting about 50% with it so that's what's leaning me to think I'm doing something wrong rather than genetics.

Rahz said:

All clones.

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Really? Where did you source the clones?

From my experience, a plant with good genetics will be visibly frosty even if it is starved of nutrients for most of its lifespan. The opposite is also true. No matter how many nutrients I pumped into a genetically bad plant, it did not help increase trichome production at all.

Can we see some pictures of the plants?

Farmer's Hat said:

Really? Where did you source the clones?

From my experience, a plant with good genetics will be visibly frosty even if it is starved of nutrients for most of its lifespan. The opposite is also true. No matter how many nutrients I pumped into a genetically bad plant, it did not help increase trichome production at all.

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I grow my own with an aeroponic cloner. I usually get 95-100% success rate. The Purple Punch does not like to root from cuttings, lucky to get +50% but it does really well once it gets in the flower chamber.

Farmer's Hat said:

Can we see some pictures of the plants?

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Yes, I'll get some pics up this evening when lights are on.

Rahz said:

I grow my own with an aeroponic cloner. I usually get 95-100% success rate. The Purple Punch does not like to root from cuttings, lucky to get +50% but it does really well once it gets in the flower chamber.

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You might need to pop some more beans until you find a keeper. If your low on seeds for those specific strains, consider reversing a clone and making some more feminized seeds. Thats what I would do.

peat is inherently acidic often with promix i add extra dolomite lime to help buffer the ph i also dont feed to run off want to keep that lime where it is. you shouldnt have to ph your nutrient solution with promix thats what the lime in the media is for if you are going to ph it 6.1 should be fine for promix. also if your in a sealed room why you only running 850ppm for co2 get that up to 1500-1600 ppm and adjust your light accordingly so they grow faster.