[zbenjii]

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?

[Dave Coulier]

Originally Posted by zbenjii

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?

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.

[spurr]

Originally Posted by 3rdEye

Just revisiting this thread.

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.

Originally Posted by 3rdEye

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.

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.

Originally Posted by 3rdEye

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.

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?

Originally Posted by 3rdEye

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

How's that sound?

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:

1. 0 to -5'F DIF by heating to 80'F during the night time. I keep my day temps around 75-78'F, with Co2 at 700-750 ppm and RH at 50-55%.

2. I am using ~50 ppm P (inorganic grow this time, using GH fertilizers).

3. I am using a 1,000 watt Digilux MH lamp for higher R:FR and B:R, as well as for green light. Powered with a Galaxy electronic ballast ("select-a-watt") to reduce flicker and increase irradiance.

4. I am using a 'hot spot' diffuser, the "Equalizer", to reduce the amount of direct light (by turning direct light into diffuse light) forming the hot spot below the lamp. Using a diffuser not only helps increase irradiance over the whole footprint, but intra-canopy too. This should help increase the R:FR ratio.

I have only carried out limited testing with the Equalizer and my quantum sensor, and I was not very impressed with the Equalizer. However, it's better than nothing and it's all I have ...

5. I am growing in a 5'x5' HydroHut (plants wall to wall) located in my grow room, to increase irradiance (by reflection) to lower-canopy/intra-canopy (even the floor is reflective). The tent should help increase the R:FR ratio intra-caonpy, the critical location to increase R:FR ratio to reduce stretch.

6. Average Daily Temperature is > 75'F.

7. I am going to hook up my UV-b lamp (mercy vapor) to provide UV-b at high irradiance. UV-b has been found to reduce stretch/internode elongation in many studies.

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.

* plants on the out edge of the canopy, if they are not in the direct foot print of the reflector, can get up to (and over) 75% of the irradiance found inside the outer edge (closer to 'hot spot'). In my grow setup the irradiance increases about 75-175 umol/area/second when the outer plants are raised about 6" above the inner plants, depending upon the location of the plant along the outer edge of the 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 ...

[spurr]

Originally Posted by inquest

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.

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.

[spurr]

Originally Posted by zbenjii

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?

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 from the higher DIF (some people suggest this is why buds can become 'more' purple with cooler nights).

[setaemies]

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: https://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

[Bongstar420]

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.

Originally Posted by spurr

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.