Hey DGC! First photo run was going great until I hit a heat wave a week ago. My LED inverters are generating too much heat and the fans just bring in hot air. My temps were 89 but with the heat wave it went to 94. Then I began dialing down the light to offset. Now temps are below 80. VPD is no longer in the 3-4 range. But I’m seeing pad levels at my tops of 250. I am in the ripening stage of flower. Between flush and late flower feedings.
My question is what should I looks out for if my plants are receiving too little light at this stage, and what is the drawback of finishing flower with low light intensity. Do I need to have 500 ppfd at minimum? I trust my Pulse Pro but my old school ppfd monitor, that’s also a ph meter, and wetness meter shows over 500 at the tops. I know that I need to provide a whole lot more info probably but I’m most interested in not killing these suckers with too much heat or low light. Or else y’all are getting hay from me at the DGC cup.
Been there, done that! Many times I just extended the dark period until it cooled off, sometimes skipping an entire day if the evening temps didn’t go lower than 90. This extends flowering time and slows ripening, less light means less biomass, but in my experience low light intensity means stretchier buds, less flower, longer flowering time, but not less quality.
I hope you get a cool spell and can crank your lights a bit. But I wouldn’t worry if not, just keep on doing what yer doing!
This was encouraging to wake up to. This resets my expectations. Around week 4-5 they got more sensitive to stressors but I showed them tough love not the care they needed. Today they were shooting new pistils across the board less than 24 hours after dimming…except 2 branches they’re dead on the vine. Luckily there is a cooling period coming into town. My goal for the next week is keep VPD in check and take what’s ready to the dry tent.
If and when I try to stick to VPD is in veg only, once my ladies are in flower VPD importance is slowly tapered down on my check list. Lowering intensity will only lighten up your total yield by not producing as much density, though intensity falls some, spectrum isn’t diminished and diode efficiency is increased. One way I’ve found to help with handling a heat wave, while trying to not turn down for what, is to boost CO2 in someway, even an oyster mushroom box can help the plants deal with the heat as long as there’s enough light intensity to support the photosynthesis. During last years heat bubble my room, at weeks 4&5 of flower, got up to 115F, I absolutely lost terps and other valuables I’d rather not think about loosing but the girls never showed signs of wilting or clawing leaves, they just prayed under the 300W LED/ 315W CMH combo I was running and I credit it to the mushroom boxes I had added the week before the wave. Best of luck sorry for the rant, that Irie dank got me like ooh ah, ooh ah.
What is your RH%? Any time I see that my temps are getting a bit high I try to add a bit of humidity to artificially lower my temps, I will just set my humidifier to 50-55% to get decent results in late flower. You must be careful especially later in flower as I would hate to be the reason for a lost harvest, but a good AC fan or Niwa controller should greatly help your chances of success. I wouldn’t worry about VPD so much late in flower as not much growth is occurring maybe just some buds fattening up. I would only worry about that humidity getting above 60-65% and temps above 78-80F, then cranking my lights as high as I can personally. Drying out your bud with too low of humidity might be as bad as too high of temps, as the air sucks the terps out of the plant through transpiration. Coming from a Texas grower I know your pain, hope you get some good jars of the DANK!
Honestly one thing I learned early in growing is. When applying co2 you can run hotter temps and higher light intensity. Maybe throwing a $35 exhale xl in the room to raise the ppm a little bit might help.
Or the other option is more air circulation and ventilation. We would need more info about yojr set up like you said. Where’s your grow at? Do you behave a lung room?
Ideally for flower formation under normal CO2 levels a PAR of 800-1000 is the goal. I would probably not trust that light meter combo at all, especially if you are dimming the light. It’s likely that meter is just a lux meter that makes some kind of conversion to PAR and if you are dimming the fixture then it’s estimates are likely to be farther off. If your light has a driver on it and you can put the driver outside of the tent then that could potentially reduce some heat in the tent but only a degree or two at best maybe. Have you considered increasing humidity in the short term to help ease the plants through this hot spell? I have heard of some aquaponic growers who run their environment in the 90s with about 70% humidity to achieve a reasonable VPD. You would just need to make sure you have adequate airflow through the canopy and have some IPM going to prevent any mold/fungus growth. Many people are not comfortable with this type of growing but it is possible if your ducks are in a row.
During the summer months it is imperative for me to run only at night. So I can use the free cool air. During the day when the lights are actually off is the only time I run the AC unit. I am under the impression that I don’t need to worry about CO2 during the night cycle. So that’s why it seems to work and I don’t have to have some sealed environment and all that stuff. That sounds like a lot of work