A Question for the 18/6 Auto Crowd?

[ExNavyInSTL]

I'm reaching out to those of you home growers who grow your Autoflower cultivars using 18 on and 6 off.

Are you satisfied with 18/6?

Are you doing fewer hours than 20/4 or 24/0 to save on your electric bill?

Is it because you just don't see the return on investment of burning more energy?

Is it because, if there is some reduced yield, it doesn't matter because you grow for your own use and 18/6 provides you plenty enough?

There is a reason I ask this. I made the decision to add a 2nd Mars Hydro SP-3000 to my 4 x 4 tent. I have one of the lights that I bought with my 2 x 4 tent, but (theoretically) gave to my wife when I decided to move up to 4 x 4. Now, I realize just how great that light is and want to combine it with another and give my wife the 400w LED I am using now.

Like anyone else, I appreciate PAR, PPFD and DLI. However, I don't want to leave some of that quality light spectrum on the tent floor if it is just a waste of money. So, I am considering going to 18/6 (from 20/4) with the, now, 600w that I have to burn.

If this seems confusing (and a total 1st world problem), I hear you. My point is I want to give the best and high-quality light to get the best plant results, but not just throw more money away than needed by running high and hot for 20+ hours.

There has to be a sweet spot that some of you have worked out, and I am curious about your logic on your decision of just how much energy you burn.

 

[Rasterman]

Take any of this with a large grain of salt:

I've read that anything over 18 hours is past the point of diminishing returns. I grew with 24 hours for awhile and switched to 18. I couldn't tell the difference in how much it grows but that's just one sample.

I was thinking the plant needs a rest and I want those plants happy. Also, it's my understanding that root growth happens at night. And finally, I remember reading years ago that the plant uses CO2 during the day while expelling oxygen but switches at night. Since there must be a reason for that, I decided to always give them a down period of at least 4 hours.

 

[Mañ'O'Green]

@ExNavyInSTL You really answered your own question. Cannabis will thrive at DLI from 43 to 60. Yields will improve slightly above 60 but it will cost more in energy than you will get back. If you need to run your lights more than 18 hours to reach DLI 43 because of low PPFD then do so up to 20/4. Plants definitely need a night time for the best quality and if you cannot get to 43 DLI on 20/4 then get more lights. If your lights are capable of 60 DLI in 12/12 then you could run that schedule without any loss in yield. There is a big advantage in this in that you can run Photo and Auto plants in the same space at the same time.

The next consideration is heat. The higher you run your lights the more heat you will get in the space. If running say 1400 PPFD on 12/12 (60 DLI) is going to give you heat issues then dropping down to 1200 PPFD for 14/10 will lower heat and still give 60 DLI or 950 PPFD on 18/6. The energy used in all three of these scenarios is nearly the same. There are small differences because of the power lost in the drivers.

The reason 24/0 got started years ago was because lights were so low in PPFD they could not even get to 43 DLI in that time. We do not have that problem now.

I run 18/6 because I live in a frikin desert and heat is my enemy. I time shift my grows so the plant's day is at night and lights are off in the hottest part of the day. I then also have time to work in the space in the morning and evening. I have run Photos 12/12 60 DLI in the summer but I grow tropical strains that can tolerate temperatures in the 90s. I time it so they are finishing in the late Fall and the temperatures for flower ripening are <80°F.

 

[ExNavyInSTL]

You really answered your own question. Cannabis will thrive at DLI from 43 to 60. Yields will improve slightly above 60 but it will cost more in energy than you will get back. If you need to run your lights more than 18 hours to reach DLI 43 because of low PPFD then do so up

MOG:

Yesterday, I bit the bullet and bought a 2nd MarsHydro SP3000. I suspect I will have zero problems in a 4 x 4 tent hitting 60 DLI in 12 hours with this pair of portable Suns.

In my case, I am lucky that I only grow what I need for my own personal consumption. So, if I get less yield than the plant's potential I think I am ok with experimenting with lesser light periods ... meaning, a photoperiod schedule for Autos.

I've settled in on how I want to grow next (stress ... for now):

(1) 4 x 4 Tent
(2) 4 x Fabric Bag AutoPots
(3) Jack's 3-2-1 salts ... modified when preflower is obvious to 2:2:2:1.2 (1.2 = MKP for the "P" Boost)
(4) 2 x MarsHydro SP-3000 Lights - Shooting for 50 - 60 DLI (no CO2 supplementation)
(5) Follow the Pulse Website for VPD Standards

Check out Coco's Testing of 2 x SP3000 in a 4 x 4 tent (fast forward to 19:37 into the video if this link doesn't take you there):
CLICK HERE for Video: 2 x MarsHydro SP3000 - In a 4 x 4 Tent

It's easy to get excited about the possibilities of growth potential with this setup after watching this test.

 

[Emerald Archer]

I just finished my first run and chose this schedule for several reasons.

primary reason was because it’s pretty close to my own body clock. My batteries charge in about 6 hrs and i turn in around midnight or 11 bells PM.

end of the day: the plant has to make some adjustments to ME and MY garden time.

So in a nutshell i got her into some nightly rituals before i went to bed, and in the morning the next day. We felt each other out and settled on a good working set of expectations that both sides mutually felt were a good set up of love and admiration.

I will kiss her soon and spread her scents ‘effects’ and overall love with some friends this summer. Its been way more fun than I have expected and look forward to the ‘gemini-grow’ I have planned for March when I can reset my laboratory and start to stash a stock of winter varietals.

 

[pop22]

One thing I don't see mentioned here is the fact that, blasting them with more than 1000 PPFD is ineffectual as it induces light avoidance mechanisms and can actually slow down photosynthesis. Now that there are PPFD measuring apps for smartphones, you have a better way to adjust your light levels. Shoot for 850-1000 PPFD in a non CO2 garden and 1200-1500 with CO2 added. I'm doing 18/6 with my PPFD averaging 850 and results have been great.

Also, you can dim you lights a bit and lower them to raise PPFD and reduce heat produced by your light if that's an issue, depending how big your footprint needs to be Most modern lighting designed for 4x4 spaces can deliver enough light for a 4x4 at 16 inches.

 

[CannabisMingus]

Are you satisfied with 18/6?

Are you doing fewer hours than 20/4 or 24/0 to save on your electric bill?

FWIW, I run 20/4 in my garage tent with los pots because I need the extra heat. I run 18/6 in my DWC system because I tried it, noticed some anecdotal improvements (pH stability increased some, potential - if slight - terpene improvement) and just kept right on rocking it. IMHO, YMMV. etc.