Popcorn Tops

Anyone got any ideas what could cause this type of bud development? I grew this strain (Alien Rock Candy) before under a different light. Was a lower powered 300watt led. The buds were massive and full of crystal. So i kept her as a mom and clone enough for a big system and upgraded the light. The new light is a Mars FC8000. Each grow was done in my rdwc system. All the nutrients were the same brand. The ec was between 1.0 - 1.4 and the ph was always hovering 5.6 - 6.2. Water temps were 60-66, air temp always 65-70 and humidity always 50-60. My lights were around 40-50% with 400-500ppfd during 12/12 transition then i slowly turned them up to 75% around week 2-3 of 12/12 giving them around 700-800ppfd. Everything was looking normal. As they continued to stretch i noticed each system had around 8-15 tops that were stretching above the canopy and the stems were turning purple. The bud development seemed to have halted. Right now i am around day 36 since the 12/12 flip and they still look as if they are day 21-25.

I tested the light ppfd a few days ago and it was around 1100-1200 ppfs which is too much unless you have co2. i dont have co2. so i dimmed the lights and raised them to 24 inches, dropped the ppfd down to 600-700. The buds are stunted and will not develop into what they should of been. The side buds and lowers look normal but because the whole plant got shocked somehow i doubt they will ever finish properly. looks like a lost grow?

Anyone can confirm what might have cause this? Attached a pic of one of the tops.

Hairs are turning brown but there are no hermies in sight as i grew this strain before as well. My 2 suspects are ppfd got to high and damaged the plants / bud development and or the vpd is too low. with the temp and humidity i was measuring around .7 kps at the leaf surface.

drills1981 said:

The ec was between 1.0 - 1.4 and the ph was always hovering 5.6 - 6.2. Water temps were 60-66, air temp always 65-70 and humidity always 50-60.

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This looks good all except the ambient temps. That's way too low for led. You could probably get away with those temps using HID but still on the lower end. Maintain a daytime temp of 80-82F and nights at 68F. 72-75F night is better.
The red upper stems are likely a response to the light intensity, especially if your lower side buds have development that's up to snuff. The plants are putting their energy into the more ideal flower sites, unfortunately it's not the tops.

drills1981 said:

Hairs are turning brown but there are no hermies in

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Common response when your pushing them hard and something is off. Get those temps up and you'll see some development.

drills1981 said:

i was measuring around .7 kps at the leaf surface.

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Way too low. Target is 1.0 - 1.1
You can up this every 2 weeks .1

After harvest or cull make sure to look over roots. More to rule it out but ya never know

I've got a plant going right now that was doing something similar with the pistils turning very early on in the cycle. I've got a bi-level multi strain going and turns out she was in a cold spot. Even tho her leaf temps were on par with others in the tent, the true ambient in her zone was lower than where my probe is placed.
I installed another fan at the top of the tent and angled the warmer air down to her corner.
She evened out and is now bulking up.

Jimski said:

After harvest or cull make sure to look over roots. More to rule it out but ya never know

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yea the roots are good. i run sterile with uc roots. everything pearly white.

i was thinking had to be lights and or vpd or both. plus this alien rock candy strain is sativa leaning pheno so a little less resistant to lower temps / humidity.

I just got back. I have 2 big 8 inch inline fans with duct boosters near the window exit. so i turned them off to stop them from sucking out too much heat and humidity, i left the little boosters on. the temp is around 77 now with the rh 55. so hopefully they can come around a bit. i know the tops are done for but it is what it is i guess. took a few more pics to get a better gauge on the issue. be nice to pinpoint for future and others.

its disheartening cause that bottom pic is what it should be when grown in perfect conditions.

It’s always a smart idea to keep cuts/moms. You’ve run her well once before, so you just gotta get your system dialed in a little better for her specific demands. Keep taking notes and writing down data points that you can come back to check on later.

MissinThe90’sStrains said:

It’s always a smart idea to keep cuts/moms. You’ve run her well once before, so you just gotta get your system dialed in a little better for her specific demands. Keep taking notes and writing down data points that you can come back to check on later.

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thank you and everyone for the replies. yea i usually have everything dialed in to a fraction. this is a new place i bought to do a quick fix for my grows. i live northern canada and it is really cold and really dry. the place i bought has a small leak in the foundation so all the insulation is torn off the blocks. been trying to squeeze out a grow before spring then i can fix everything up and seal it. i think we can narrow it down to the vpd. based off my temps and humidity we were hovering around the .5 to .7 kpa range when it should of been around 1. plus with the added ppfd being around 1100-1200 i think it might off been a double whammy. not to mention in the night with the lights out i could only estimate that the temps got even lower, probably around 60 degree range. so all is good. i think it safe to say she is over, but i will ride it out since i dont have anything in the wings just yet to do the next grow.