EKG Cal Canna
Well-Known Member
I have some strains that stems run light green start to flush,I have another that stems turn purple after 2 wks of flower but it hasnt changed the quality of smoke!
Red/purple stems and mag deficiency with LEDs?
- Thread starter Aheadatime
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Grow Lights Australia
Well-Known Member
This is a known issue and has several causes. LEDs do not emit much infra-red (heat) especially compared to HIDs. This means there is less leaf transpiration but it also means pots don't dry out as fast. LEDs are great in summer and warmer climes, but can be challenging when temperatures are cooler. Conversely, because LEDs are generally high quality light, they can accelerate photosynthesis which leads to a general nutrient deficiency which might not be experienced under other lights.
When transpiration and evaporation around the root zone slow then you need a higher EC in general because water is not being evaporated at the same rate, which means the EC is comparatively lower at the root zone compared to pots that dry out faster. Transpiration affects calcium and magnesium uptake, but wet pots affect phosphorous uptake.
You need to both increase the EC in the reservoir to maintain the correct EC at the root zone, and increase Cal-Mag to offset the reduction in transpiration. If you have a good nutrient to begin with that already has high levels of Ca Mg, you may not need to add Cal-Mag – simply increase the pH to 6.3-6.5 to make both more available. But be careful not to go too high, as that will lock out your heavy metals such iron, copper, boron and especially zinc.
In a nutshell, use a good quality nutrient with adequate Ca and Mg. Keep your pH on the higher side (5.8-6.3 in coco or hydro) and don't let it get too high. Increase your EC slightly (say 10%) to keep up with growth and ensure adequate EC at the root zone, and don't overwater until the roots are established to prevent root stress that causes phosphorous and other lock-outs that lead to red stems and yellow leaves. It is also important to make sure your lights are not too powerful.
The red stems and yellow leaves are not really a CalMag deficiency, but an overall deficiency as well as root stress related to above. They can also be related to light stress or a combination of all these things. LEDs do not appear as bright as HIDs but are very powerful. They have more blue light in them (and UV in some cases) which is more powerful than red light and can stress plants faster. So dial back the light and water and increase the nutrient or foliar feed until the plant recovers. After a while you will get the swing of things.
Have a look at our Instagram page – you won't see many if any red stems and yellow leaves under our lights because most of our growers have experience: https://www.instagram.com/growlightsaustralia/
Good luck!
youraveragehorticulturist
Well-Known Member
Wow, great information/great post!
You mentioned the "blue" LED light being "more powerful". Does this mean my "grow" spectrum, blue light heavy LED will blast my plants more than a red heavy, Flower spectrum LED at the same wattage?
Can I increase transpiration at lower temps by increasing airflow. Or like blowing more fans across my leaves?
Less transpiration and low temps lead to damp soil. Damp soil leads to root stress and stuff. Can I use fabric pots and more aeration and expect better results under LED?
Raising ambient temperature fixes most LED deficiencies when everything is correct otherwise.
HID grow temps around 75 will have healthy plants... put those under LED at 75 and youll see deficiencies, especially cal mag...
Raise LED grow room temps to 78-85 and they will get healthy.
Surprised nobody said this yet. Many LED manufacturers also make this point.
It has to do with the LEDs not putting out much or any IR heat to warm the leaf surface temperature properly, like the sun does, and MH/HPS/CMH do... so you need to warm the room to compensate.
HID grow temps around 75 will have healthy plants... put those under LED at 75 and youll see deficiencies, especially cal mag...
Raise LED grow room temps to 78-85 and they will get healthy.
Surprised nobody said this yet. Many LED manufacturers also make this point.
It has to do with the LEDs not putting out much or any IR heat to warm the leaf surface temperature properly, like the sun does, and MH/HPS/CMH do... so you need to warm the room to compensate.
Comparator
Well-Known Member
My leds plants dry just as faster or faster then hps using targeted Spectrums. Leaf Radiation or not. Much higher leaf absorbstion rates.
Grow Lights Australia
Well-Known Member
For the same wattage no, because it takes more electricity to make a blue photon than a red photon, so watt-for-watt there will be about 1/3 fewer blue photons than red. However, those blue photons will carry about 50% more energy than each red photon (comparing a 400nm blue to a 600nm red). Photons that are not absorbed, reflected or fluoresced will be converted to heat which can raise leaf temps. This can help with transpiration – up to a point.
You would think that fans would help with transpiration but there is evidence that increased wind movement further cools the leaf through evaporation that can close stomata in some species and actually reduce transpiration. One of the functions of transpiration is to cool the leaf when it is warmed by infrared energy. Cooler leaf temps can affect uptake of phosphorous.
You can use fabric pots but that is not a cure for overwatering plants to begin with. Plants can still grow nicely under led in cooler temps if you know how to feed them. You can also try having your lights on during the day instead of night when it is warmer. All chemical processes including the organic processes that create life speed up when warmth is increased. It's not just plant growth.
Grow Lights Australia
Well-Known Member
IR penetrates the leaf and warms water molecules under the surface increasing the overall leaf temperature.
Grow Lights Australia
Well-Known Member
The pots won't dry as fast so you have to rely more on the plant taking water up.
youraveragehorticulturist
Well-Known Member
Thanks for straightening me out man! I appreciate the detailed reply.
I've got some purple stems and wet pots right now. I'm off to adjust some fans and the AC right now!
Comparator
Well-Known Member
I think my leds plants dried just as fast because I do not use upper canopy fans. Only one big oscillator that's plained out with the ceiling. Cools the lights if anything. Most of my fans are under the canopy pushing air across the floor and Potts. Fabric Potts. Above you had mentioned the upper fans cooling the leaves, slowing transperation. That's prob. why I like growing around 78•f , about 50% of the bloom phase. Lights need to have Far Red , n/ir too. As you said, that excites the molecules within the leaf causing then to bounce off each other, in turn generating heat within the leaf. Certain blues i use increase stomata opening & production by up to 30% as well. When environment, spectrums & intensity is all in line, one has then optimized the playing ground and then can see the true differences with healthy plants.
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Comparator
Well-Known Member
Actually the plants responded better using higher K-temps with leds. When the spectrum is well balanced and not to high of a ppfd then your plants won't get the purple stem burn. Using Epsom helps and so does air movement not direct wind. Bottom and top circulation. Overly White dominant leds will cause this everytime pretty much. A 38-55k may work a little better but if not enhanced and reduced you may have the issue. Don't be in wet cold Potts too, that doesn't help. Have n/ir in your led spectrum too, seriously.
If you need to cure your Purple stemmed led damaged plants immediately then switch to some CMH or MH.
Prawn Connery
Well-Known Member
No. That is not the solution.
The first thing you need to do is reduce the light intensity and allow the pots to dry out. I see a lot of new LED growers going too hard for the simple reason that they don't realise how strong LED light really is, as it is not accompanied by the same amount of IR (and I mean "IR" heat, not Far Red), and is also spread over a wider area compared to HIDs. A lot of growers also can't reconcile that a 350-400W LED can produce the same amount of light as a 600W HPS.
This all gives the illusion that LED is not really as strong as it is and many new LED growers stress their plants believing their light isn't strong enough when the opposite is the case.
Red stems can be genetic, but the genetic expression is usually caused by lower temperatures that slow magnesium and especially phosphorous uptake.
There are also different types of "red" stem. Purple stems – the ones normally associated with genetic expression – are normally a sign of P, and to a lesser extent Mg, uptake being affected by temperature. Pink stems are caused by anthocyanin stress pigments usually due to light and/or root stress.
One exacerbates the other. Light stress will slow growth, which in turn will slow water and nutrient uptake from the root zone, which in turn may start to suffocate the roots if the media remains too wet for too long, which will further slow growth in a negative feedback loop. You need to break the cycle by reducing the light intensity and allowing the pots to dry so that the plant can recover before it starts to grow normally again.
And contrary to popular belief, pink stems are not a reaction to having too much red in the light spectrum but in fact the opposite – blue light carries more energy which causes more stress when overall light levels are too high, which causes more anthocyanins to be released which are expressed as bright-red of pink-coloured stems and petioles (as opposed to deeper red/purple).
It's not that hard to grow healthy plants under LED, but it does take a little bit of adjusting to the new light.
Comparator
Well-Known Member
Yes, I agree unless you have allot riding and needed your veg into flower immediately. Then do everything you said next veg.
Im sure there are other reasons for it but take a red heavy led spectrum like a burple that has heavy reds, little blues and lessor green then you'll get red stems. Not really harmful to growth only expression. Purple stems which can happen from high intensity white lacking fillers. Yes I veg with leds but when push came to shove during the learning curve cmh / mh was a quick fix while I futzed around dialing in the led and plant needs.
Not swaying just saying.
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Prawn Connery
Well-Known Member
I appreciate you are trying to help – and I agree that what you are saying is technically true – but I would also suggest that what you are really doing when you remove the LED and replace it with a HID (CMH, MH or HPS) is you are introducing more heat via infrared which increases evaporation at the root zone (dries the pot) and increases transpiration at the leaf surface (which also dries the pot by increasing nutrient water uptake into the plant), which can also reduce water stress at the root zone.
HIDs convert more energy to IR than PAR, which can also reduce the amount of light stress the plant is experiencing (if you swap out 400W of LED for 400W of CMH, for example). So all these things do the same as reducing the LED light intensity and allowing the pot to dry.
It's just another way to skin that cat.
And you are right about the learning curve. I was in denial for a long time when I first switched to LED thinking how could I possibly be giving my plants too much light when I replaced a 600W HPS with 450W of LED. But I was, and it was only when I started reducing light levels and compensating with higher ECs (due to reduced transpiration and less evaporation at the root zone) that my plants started to thrive.
Here is my grow tent as of today. Check the red stems on the plants closest the lights in the middle of the image. That's light stress (these lights have added UVA). But I can put up with a small amount of light stress on some of the branchs to ensure enough light penetration to the rest of the canopy. Plus that particular strain (Tangerine Sorbet) grows monster buds when you hit them with 900+ PPFD, so I can tolerate a little bit of light stress for the greater good. As long as the plants remain healthy and vigorous, a few red stems are not going to hurt.
zeem
Well-Known Member
That's interesting. Assuming same medium exactly. Can you mention the cultivars involved. Maybe it is relevant. I dunno.
zeem
Well-Known Member
Personally, I have experienced a red streaking stem issue for more than a decade with my cultivar. Sometimes more than streaks... in some areas where there would be little green visible. As a noob grower in 2009 I was way too fancy-pants before I truly knew my plant and process. Ran coco and dead-trients forever. It was not until my wife stuffed some discarded clones into a mix of FFOF/Happy Frog that I realized our cultivar could have green stems during the entire life cycle; and watered with plain water too.
But like the amateurs that we are, we were still using a nu..., err I mean, dead-trient to adjust pH of the water. I need to learn to use a natural pH down or maybe none. I dunno the answer to that "down or none" yet.
My belief system is that this red stem and petiole condition is about available nutrients due to pH. I am not experienced enough to know empirically if different cultivars can be at their optimal potential at different pH.
We all got our own belief systems. Mine regarding the cause of red stems "Works for me" currently on my cultivar.
I maintained only one cultivar during the last 13 years.
I started my second cultivar, ever, last week.
But like the amateurs that we are, we were still using a nu..., err I mean, dead-trient to adjust pH of the water. I need to learn to use a natural pH down or maybe none. I dunno the answer to that "down or none" yet.
My belief system is that this red stem and petiole condition is about available nutrients due to pH. I am not experienced enough to know empirically if different cultivars can be at their optimal potential at different pH.
We all got our own belief systems. Mine regarding the cause of red stems "Works for me" currently on my cultivar.
I maintained only one cultivar during the last 13 years.
I started my second cultivar, ever, last week.
Rocket Soul
Well-Known Member
If youd like a different perspective on purpling stems and petioles you can google High irradiation response. Or was it reaction instead of response, maybe throw in horticulture as sesrch term for good measure. Long story short, raise temps a bit. Higher temps seems to inhibit anthocyanin production when the plant suffers too much light. But there certainly seems to be more to it as for susceptibility to HIR.
plumsmooth
Well-Known Member
IF you want to succeed right away pm me 
zeem
Well-Known Member
Is a leaf chlorosis commonly associated with the trifecta of:
I think a root zone problem persists in my situation. I had advice from a plant expert suggesting that bad bacteria can infect a soil in ways that can cause the kind of chlorosis I am experiencing (That is beyond the larvae eating my cooking root zone). Actually, I had an opportunity for my sitting soil to potentially contract a bad bacteria, as it sat for months before I used it. (mistake number 1, perhaps)
I'm going to try raising my temps to see if this LED + Too low temperature thing is a valid factor in my problem.
Does it help to post the manufacturer of my LED setup. I am using it at 50% power. I have a Luxx 645 LED Pro.
Thanks everybody!
- Colder temps, such as below 55
- LED
- Purple stems and purple petioles,
I think a root zone problem persists in my situation. I had advice from a plant expert suggesting that bad bacteria can infect a soil in ways that can cause the kind of chlorosis I am experiencing (That is beyond the larvae eating my cooking root zone). Actually, I had an opportunity for my sitting soil to potentially contract a bad bacteria, as it sat for months before I used it. (mistake number 1, perhaps)
I'm going to try raising my temps to see if this LED + Too low temperature thing is a valid factor in my problem.
Does it help to post the manufacturer of my LED setup. I am using it at 50% power. I have a Luxx 645 LED Pro.
Thanks everybody!