Why do I always smell the plants outside the garden at lights out?

[hush]

I have noticed this before, and I even mentioned it in my Satori journal a few years ago. Why does this happen?

Even though I have a perfectly effective carbon filter, and proper negative pressure, and I never smell anything at any *other* times... I always smell the flowering plants briefly at the moment the lights go off. It is not imagined, either, as my wife confirms she smells them too during these moments. In fact, I'll be out in the living room watching TV or something, and I'll catch the whiff, and instantly know that it's 7pm and that the lights just went off in the garden, then I'll look at the clock and this is confirmed.

So my questions are, WHY does this happen and HOW does this happen?

 

[JimmyRow]

I've noticed more smell from my room then as well. I've always shrugged it off to the spike in humidity as the dark period starts, and contrasting temperatures. Just a guess.

 

[LittleAmsterdam]

Plants inhale CO2 when the lights are on and exhale oxygen during the off hours. What you're smelling is the fresh oxygen produced from your plants infused with their natural aroma

 

[BullnAChinaShop]

Yep, I too find this to be the most pungent time of day.

 

[Kcar]

You smell your plants at lights out because your plants are still fully
transpiring for 10-15 minutes after the light has gone out, but now there
is no heat source to dry the air. Carbon filters lose their effectiveness in high
humidity situations. So some of the terpenes come through with the water molecules.
Happens outdoor too, at sundown.

 

[LittleAmsterdam]

Plants transpire Oxygen when the lights are out.

 

[JimmyRow]

You smell your plants at lights out because your plants are still fully
transpiring for 10-15 minutes after the light has gone out, but now there
is no heat source to dry the air. Carbon filters lose their effectiveness in high
humidity situations. So some of the terpenes come through with the water molecules.
Happens outdoor too, at sundown.

this is what i was getting at, only better said. not so say LA is incorrect.

 

[irishdude5186]

You smell your plants at lights out because your plants are still fully
transpiring for 10-15 minutes after the light has gone out, but now there
is no heat source to dry the air. Carbon filters lose their effectiveness in high
humidity situations. So some of the terpenes come through with the water molecules.
Happens outdoor too, at sundown.

I was told not to go over 70% RH or the performance of my carbon filter\life cycle was reduced. So I did a quick google and found this:

"Temperature and humidity have a major influence in how effectively a carbon filter will work. The absorption capacity of carbon decreases at higher temperatures therefore it is important to adjust air flow into the filter with temperature fluctuations. A remote thermostat should be used with the filter to adjust air flow according to temperature. Carbon’s capacity for absorption diminishes with extremely high relative humidity. As a grow room should never be allowed to exceed 60% humidity this should not effect your odour filtration."
Source: http://www.hydroponics.com/howtoinfo/hydroponics articles/carbon_filtering.html

 

[irishdude5186]

"What is the Maximum Temperature/Humidity I can run my filter at?

The maximum recommended temperature that you can run your filter at is 80°C / 176°F

Above 70% humidity the water molecules in the air start to get stuck in the carbon pore structure and slowly diminish the life of the filter."

Source: http://canfilters.com/faq.html

 

[JimmyRow]

I run 70% RH thru stretch. But def not during flower when the filter needs to be doing its job. Good info. Thanks

 

[hush]

Wow you guys are helpful! I have to say, the bit about the light turning off and subsequently the humidity rising because the heat is gone too, really does make sense. Yeah, that's gotta be it. I know no air escapes from my closet except for through the carbon filter, and that is a fact. So yeah, something happens during the 5 minutes right after the lights turn off, that is allowing the air coming through the carbon filter to NOT be filtered out.

Humidity would do it.

But why does it only last 5 minutes, instead of all throughout the dark period? Is it because the plants only transpire for a few minutes after dark period begins? I guess that would make sense too.

So it seems to me that the only way to completely eliminate this brief whiff from escaping the grow room every night is to have the exhaust air actually run through a dehumidifying chamber of sorts before exiting through the carbon filter. Has anyone ever tried running their ducting through some kind of an inline desiccant bucket or something of that nature? Kind of like the same concept as a carbon filter, but using desiccant instead of carbon?

The only reason why this is a concern to me is I apparently won't ever be able to have company at my house at 7pm, or they will smell my garden! I suppose I could hook up a ozium dispenser to a timer and have it go off once a day at 7, as a worst case scenario.

 

[JimmyRow]

Ona gel works OK and my wife really likes the fresh linen scent. If its a huge issue. You could get an ozone generator, and set a timer for it to fire up when it gets stinky.

 

[Kcar]

But why does it only last 5 minutes, instead of all throughout the dark period? Is it because the plants only transpire for a few minutes after dark period begins? I guess that would make sense too.

Think of your plants as solar powered water pumps. Light goes out, plants keep pumping for a few minutes.

Outdoors it happens much slower as the light tapers off.

Also, the bulb was providing heat. Once the temp starts to drop, the RH starts to rise.

I try to counteract this by running my exhaust fan for 30 more minutes than my light + 15min per hour of darkness.

 

[hush]

Right on. My exhaust fan never turns off, though. But still, I think the same theory applies here. Suddenly after the light turns off it gets cooler in there, yet the plants are still pumping out as much moisture as they were all day long, and without the light's heat, that moisture makes it to and through the carbon filter, rendering it briefly ineffective?

At any rate, I'm just going to start dispensing some ozium via a timer every night at 6:55. That should cover the brief aroma.

 

[Javadog]

You smell your plants at lights out because your plants are still fully
transpiring for 10-15 minutes after the light has gone out, but now there
is no heat source to dry the air. Carbon filters lose their effectiveness in high
humidity situations. So some of the terpenes come through with the water molecules.
Happens outdoor too, at sundown.

Excellent response!

Thanks for taking the time.

JD

P.S. I am in the last couple of weeks from the end of my first crop
cycle, and, for whatever reason, I have my filter->lamp->fan->exhaust
set to turn off when the lights go off. Is this not recommended?

 

[noyd666]

Excellent response!

Thanks for taking the time.

JD

P.S. I am in the last couple of weeks from the end of my first crop
cycle, and, for whatever reason, I have my filter->lamp->fan->exhaust
set to turn off when the lights go off. Is this not recommended?

same as k. car above you.

 

[Javadog]

Doh....I got that...now.

And with a "reputation beyond dispute" I suppose that I have my answer. :0)

Thanks,

JD

 

[JimmyRow]

Keep an eye on temps RH. I have my filter set up to run for 15 min every hour during lights on and 15 min every 2 hours at night. That controls odor enough for now, but doesn't totally dry out my room and let's the temps stay up. But its all about keeping a happy place for plants to succeed, and a safe place for you. I keep air moving within the room 24/7.

 

[OldSkoolKlein]

So how would that theory apply to a tent grow? Size of tent would be 3ft X 3ft X 5(& a bit) ft (or in metric 80X80X160cm). I was thinking just turning off lights when in 12/12 but have fans going 24/7.

 

[JimmyRow]

I'm running a tent, only larger. My climate has VERY low RH. So whenever i exchange air, all of my moist air is removed and replaced with cold ass bone dry air. Not what im looking for right now. I play with exhaust fans, light fans, humidifiers, heaters, ect...until I achieve desired temps and humidity levels.