Leaves slightly droop 3 hours before lights off

[OG Tree Grower]

Been dealing with this for weeks and I can't quite peg what's going on.

It's environmental for sure, I threw a few dirt plants in the room to help trouble shoot and they also droop . Indica strains droop first then sativa an hour later.

Everything points to heat/ light stress but all my shit is in order and there shouldn't be any issues.

No bugs or parasites that I'm aware of and I looked with a scope for several hours

Any ideas?

Temps are 78-80
Humidity 65-70%
Res temp 69-70f
Veg cycle
Plants are 30" tall and feeding 1100 parts
Strains are familiar, one is picky the other you couldn't kill if you tried but both are showing the same problems.

Plants are still growing 2" a day so it's not stressing them to bad but I'm defiantly losing a few hours of growth every day and it's pissing me off

 

[Miraculous Meds]

pics? whats ur light schedule?

 

[OG Tree Grower]

18-6, I don't do Picts right now. But just normal droopy leaves. Nothing fancy to see

 

[OG Tree Grower]

I'm worried they got tripped into flower somehow but I don't know how it could have happened, timers and environment have all been spot on and both strains are doing it,but I really don't know what else it could be. I've never heard of this happening before but I guess I'll know in another week

 

[rykus]

When the root mass of the plant is overgrown by the green canopy, they sometimes can't support full vigorous growth for 18 full hrs, so as a natural defence the plant starts to shut down its activity to conserve energy and start the transfer energies or sugars that are part of the dark cycle...

If the plants are young sometimes I will manually turn the lights off a little early till the roots catch up, if you have digital ballasts you could dim them for a week and see if they respond to that, as an extreme you can also remove some new growth like top the plants and see if they even out.

I have only seen damage in extreme cases such as a rough transplant in a hot dry room, or way intense light. But in my mind they are doing some damage in this weakened state, that is why I will turn lights out... Getting the humidity way up can help too IMO...

 

[soil margin]

The fact that the indica and sativa strains are drooping at different times makes it seem to me like it has to be a genetic issue. Different strains can perform different amounts of photosynthesis during a given time period and once the plants have received the maximum amount of lumens that they can productively use in a day it would seem a natural response for the plant to start drooping. Basically as far as the plant is concerned, it might as well already be lights off because it's gotten as much light as it needs for a 24 hour period, so it's not going to waste energy holding the leaves up to catch any more.

My suggestion would be try an experiment by shortening the light period by a couple hours and see if the plants are still drooping a few hours before lights off. I would guess that fixes your problem. Remember that the internal chemistry of the plant (which is dictated primarily by genetics) is going to be a limiting growth factor once you've maxxed out the amount of productive lumens the plant is getting everyday.

 

[OG Tree Grower]

I agree and understand what your both saying, but I've been growing these strains for a year now for over a year. The rootmass are very good, buckets are 30% full of roots and the plants are 30" tall.

I just changed bulbs this run and still have the plants in tight to the lights since there small enough so maybe it's like you said, they have used up all there energy for the day and that makes sense because this room had no co2, the others do. Thx guys. Gonna fire up a burner and see if that helps

 

[OG Tree Grower]

The room is not sealed and cooled via air exchange, I can't get the co2 above 700 parts and was burning wfo with a 6 burner so I backed the plants off the lights a few inches and lowered food to 900ppm instead . I really apreicate the help

 

[OG Tree Grower]

Update. both strains showed immediate improvement when backed away from the light, they made it through the whole 18 hours without issue yesterday.

The only part I don't quite get is that I had no bleaching or scored leaves, usually , actually always I get those as warning signs. This time for whatever reason they just quit photosynthizing without warning. Glad that's over with

 

[delta9nxs]

what you just experienced was the plant's photosynthetic apparatus being overloaded by light.

you obviously have intense lighting and reached "the wall" as described by numerous growers. many have described reaching this point in flower approx 8 hours into the period.

this is where the total flow of light in any given period exceeds the plants ability to process that light into photosynthate.

you have already found one solution, which is to back the lighting or the plant off reducing instantaneous flow.

another would have been to reduce the hours of light reducing total accumulation during the period.

i have vegged under very intense lighting before using a 8/4/8/4 light regimen. this is 8 hours on, 4 off around the clock giving 16 hours of light in a day.

this bombards the plant loading the apparatus then allows it to process or reduce it before the next photoperiod.

i have gotten more growth in a 24 hour period using this than 24/0, 20/4, or 18/6.

it's not about hours of light, it's about total light delivered to the target.

your different strains have different metabolisms so react at different times.

you did not experience bleaching or damage because the instantaneous flow of light was not intense enough to cause it but you were close.

the maximum rate of photosynthesis in cannabis occurs at 1500 umols of flow. it is flat from there to 2000 umols and then drops off sharply, causing photo-inhibition. which is a slowdown of plant metabolism.

you were probably not exceeding 2000 umols at any given time but your total mole count at a certain point in the period exceeded the plants capacity to process.

if you had a quantum meter you could have measured the instantaneous flow and computed the total mole count by multiplying the umol reading by 3600, which is the number of seconds in an hour, x the total number of hours in the period, (in your case 18), and dividing by 1,000,000 which is the number of micromoles per mole.

if you were delivering 1500 umols:

1500 x 3600 x 18 = 97,200,000 / 1,000,000 = 97.2 moles per period.

one hell of a lot of light. the most sunlit places on earth don't get more than about 72 moles per day.

i can tell you from experience that a 1k hortilux hps at 16" delivers 1500 umols as a rough reference.

i have found that running the lights in the vegetative stage at the distance to produce about 1000-1200 umols while giving them a break once in a while gets faster growth than longer, more intense periods.

i hope this helps.

 

[soil margin]

Thanks for the indepth explanation delta. Nice having that put into simple math.

 

[OG Tree Grower]

Thanks for that indeed delta, a very good explanation .

Yes it was quite an oversight on my part. I always run sealed or semi sealed rooms with co2. And yeas I had them about 16"-20" away from bran new bulbs . There a lot happier now that there 24" away. About 55,000 Lux