Control red to far-red light ratio to limit stretching

great info on this thread. Not sure if this was already posted here but potassium reduces the amount of water the plant can uptake. ash contains some potassium.

question: does anyone know what would happen if you allowed your night time temps to be higher than your daytime temps?

zbenjii said:

great info on this thread. Not sure if this was already posted here but potassium reduces the amount of water the plant can uptake. ash contains some potassium.

question: does anyone know what would happen if you allowed your night time temps to be higher than your daytime temps?

Click to expand...

Short term it may not be a problem. You would also have a greater impact on plant stretch, but if done long term it can result in chlorosis.

Keep those day temps higher.

3rdEye said:

Just revisiting this thread.

Click to expand...

Me too, I have been offline for the past couple of months. I am just responding to older (and newer) posts now. Sorry about the slow response.

3rdEye said:

Due to a series of funny and fortunate circumstances i'm getting a new 1KW horti Super HPS. I also have a 400W Eye Blue MH. Even though the Blue has much lower output I do hope to see some reduced stretching using this combination as opposed to the HPS by itself.

Click to expand...

You may, blue and green are helpful in that regard. However, they are helpful for different reasons, e.g., lots of green can 'switch' a plant to slow down growth rate.

3rdEye said:

My idea is to start the day with the 400 for the first hour, then add on the 1K for the middle 10 hours, then finishing with the 400.

Click to expand...

Can you run both at the same time? Do you have reflective surfaces (Mylar, Orca, etc.) around the canopy, or are the plants 'in the open', like sitting in a big room?

3rdEye said:

If luck permits then i will also be able to utilize 0 DIF strategies to examine stretch some more.

How's that sound?

Click to expand...

Sounds good to me, but switching lamps seems kind of labor intensive, no?

FWIW, I am pre-flowering my grow now (started about 4 days ago). I am using a few methods to help control stretch:I am growing 20 plants, just over 1 per square foot. The outer canopy edge of plants are raised from the floor about 6", the plants inside the outer canopy edge are on the floor. Using 'stadium' style setup for horizontal lights can help reduce stretch of the outer edge plants by increasing irradiance* to canopy and intra-canopy, increasing the R:FR ratio intra-canopy.
I topped the plants (for a 2nd, and last time) about 2 days before I switched to flowering light schedule about 4 days ago. They are about 15-18" tall at this point, so I need stretch control or they could get too tall for the tent using a big reflector (Blockbuster 8"). The plants (19 [fem] GrapeGod from NextGen and 1 [fem] Blue Fruit from Dinafem) are not stretching as much as they would otherwise, IMO. I have been using 0 DIF for about a week before I changed lighting schedule. Time will tell how well this works with GrapeGods ...

inquest said:

Thanks for the great info Spurr! Right now I'm running a SE Asian microgrow and can use all the stretch reduction I can get!! I'm a bit limited in active temp control, but Ill document pertinent info as I progress. Also, I'm open to suggestions, and you're all welcome to be part of my little experiment.

Click to expand...

I know this is an overly late response, but you could try using a shot(er) daylength for pre-flowering to help reduce stretch, if the irradiance is high enough (re Daily Light Integral). Too few hours and too little irradiance can make plants stretch. I have been planning on testing a 8 on/12 off light schedule for pre-flowering to see the effects on stretch, under high irradiance.

If you grow with inorganic fertilizers you could limit P (elemental), lower-sufficient P can reduce stretch. You could apply to < 60 ppm, maybe start a week before pre-flowering. FWIW, I use < 60 ppm P in all stages, I am testing ~50 ppm now.

Adding reflective material around the canopy can help increase R:FR ratio.

One other option you have, off the top of my head, is to work with the canopy. If it's closed, open it up a bit, either by moving around branches and leafs, SCROG, or trimming. If you let more light into the canopy you will increase the R:FR ratio intra-canopy.

zbenjii said:

great info on this thread. Not sure if this was already posted here but potassium reduces the amount of water the plant can uptake. ash contains some potassium.

question: does anyone know what would happen if you allowed your night time temps to be higher than your daytime temps?

Click to expand...

What Dave wrote is correct, over the longer term negative DIF, and even zero DIF, can cause chlorosis and other problems. Often negative DIF has a bigger impact upon stretch than does zero DIF. Using negative DIF is best reserved for pre-flowering (1-2 weeks), and maybe zero DIF a few days to a week before the light schedule switch to pre-flowering.

During veg and flowering, like Dave wrote, a positive DIF is ideal, but not a large positive DIF because it's good to keep the Average Daily Temperature above 70'F. In flowering a higher DIF than in veg is OK and can help make buds and leafs more colorful due to increase of some anthocyanins https://secure.wikimedia.org/wikipedia/en/wiki/Anthocyaninfrom the higher DIF (some people suggest this is why buds can become 'more' purple with cooler nights).

Thank you spurr and others for the great topic, lots of good information here!

I read this thread a while back and today stumbled upon this: http://www.ledgrow.eu/

This guy did a small comparison test with different lights, using blue/red, blue/red/farred and blue/red/740nm cherry red. The results lead me wondering that what are the exact "far red" wavelengths to produce elongated internode spacing and what are beneficial.

edit: Only few grows posted using these EVOLED lights, but I was wondering about the node spacing, as these lights don't really have a lot of output in the far red range. Interesting thing is, that with very low irradiance levels and less than "full" spectrum, they still do produce impressive results. https://www.icmag.com/ic/showthread.php?t=221916&page=5 https://www.icmag.com/ic/showthread.php?t=215147

Early morning when its cold and not that bright eh an we are talking dry weight increase of harvestable product? Maybe the growth is from yesterdays work?

Daylength for cannabis is no longer meaningful unless you are talking about specific cultivars...most cannabis out there probably responds to 24/7 the best...I definitely get slower veg doing 4-6hrs off, but I grow only stuff that has been bred indoors for generations with outdoor exposure being limited. I throw away seedlings which do not grow well in 24/7.

Basically, you have a general rule of thumb which cannot be applied to all cases..for cannabis, you could say 24/7 will usually outperform otherwise only because selection under that regime is most frequent in the current cultural environment.

Its similar to HPS...rule of thumb, HPS is best yields..but most stuff is selected under HPS..

I bet you can get stuff to yield under halides like they were HPS with enough pheno surfing.

Those studies are probably not of plants which are almost entirely grown and selected indoors.

spurr said:

Yup, GA3 is a main factor. Same with DIF...


Nice, I would like to see that, and good job on the A and the ass! View Image




Here are some good papers about LAI, PPFD-I and RUE, taken from the many other papers at this good resource from the University of Guelph "Plant-BIO-3110 Crop Physiology" (link)

Interception of PPFD by a crop canopy

Leaf net photosynthesis

Canopy photosynthesis I (Distribution of Absorbed PPFD within the Crop Canopy)

Canopy photosynthesis II (Whole Canopy CO2 Assimilation)

Canopy photosynthesis III (Canopy Photosynthesis Calculations)



Don't try to tell some other growers that! View Image I got majorly hated on for stating the same thing as reason to not use 24/7. Also, I read a great study showing plants grow the most during very early morning hours (using a neat tool the measured growth as millimeter per hour), and second most at night. That would make sense considering GA3 increases most in very early morning hours due to DIF.

Click to expand...

After working at a few grow companies in Denver they changed my mind about far red inadvertently. They would lean into the stretching because neither had switched to LEDs, and I think it just ended up in bigger plants with bigger buds in shorter time.

Maybe repeated stretching in healthy plants gives it an advantage, because it would simply have a vascular system that’s much larger over time. Especially when you lollipop trim on top of that.

In my own grow, since I’ve always had LEDs, I think supplementing with far red would give me a better version of what they’re doing because of the cost of heat and cost of electricity.

From ‘migro’s’ stuff on YouTube with his fancy equipment it showed that was basically the only difference in wavelength between CMH CHPS and LED

Then again I am more inclined to take the corporate approach to production now, where you have 100 day harvest cycles and keep moving.

My new setup is gonna have it if anyone wants updates, running 2 maxsisun MF2000s and I’ll add the 30w supplemental far red bar as the only lights for my flowering room. The maxsisun already has some far and deep red in it, I’d go for a 15 or 20 watt if they had it, but I’ll see how it goes.

UnGolpe said:

I think it just ended up in bigger plants with bigger buds

Click to expand...

Also extra far red is more in line with the suns spectrum which apparently my mostly white LEDs are advertised as closer to than HPS already.

Given my experience growing plants outdoors a lot before indoors, I can see the difference that spectrum makes. It’s right in line with the other stuff pointing me this way, has me really excited to verify honestly. I’ll also have a single UVB florescent for the 3 of them which will really push it over the finish line I think, and get it closer still to the suns spectrum

Just been wondering about a couple of questions,,

1,,how does the dump apply to tank temperatures in nft system where you can control precisely the temperature of the roots and the ambient temps?

2. How does the dump apply to "fading" and turning everything purple in the last few weeks,,,I know spur said prolonging the dump is not advantageous during normal flower time,,but what about the flush and the fade?,,,,

3. do the lower temps have any effect on terps?

4. Would it be a good idea to use 5v led strip (4 red 1 blue) lights for directly underneath the canopy pointing up?,,, (my plants are very small I have a limited hight of 1.2m)