LED feed demands

Top dressed @ transplant, used a handful of Espoma @ flower.
Not feeding heavy at all.

h.h. said:

Top dressed @ transplant, used a handful of Espoma @ flower.
Not feeding heavy at all.

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You're just using the rock phosphate, right?

Or something else?

Also, what distance are you keeping your lights?

Well I'm struggling to advance past 30w per foot. E.C going in at 2.2 and coming out at 1.4 is making me feel maxed out. I have to push the food higher, but recall 2.7 was once thought the most with atmospheric co2. And I need to think about ec2.5 at 30w. My truncheon is going to run out of lights before I do. 25c leaves in 28c ambient, 65%. I'm going to have to lower that 65%, to increase watering frequency. In an attempt to get more food in that way.

I can't usually have such a humidity, but the leds need little extraction and I picked up a big humidifier. The change in conditions is certainly playing it's part in my feed demands. The 600w control is rocking, and it shouldn't be at this EC. So the RH is having really quite an effect.

Curious, who has a cool and dry flowering environment with their LEDs??

Cool and dry conditions suck for soil, since the microherd much prefers warmer days, but it's what I use with hydro. The transpiration rate is decently high. Normally, this high of a transpiration rate, combined with a full pH swing, allows me to keep the feed strength rather low.

Coolest I can get with lights on is about 78 degrees at 600 watts per rig. That's with my 8" fan on 100% through my filter.

When I increase the size of my air intakes after this harvest, I'm hoping to get at least a couple degrees lower.

Basement temps are 65-70 degrees except in mid to late fall when the ground is still nice and warm and I'm not running the air conditioning in the house because the outside temps are nice and cool.

Great thread.


I switched to quantum boards myself a couple weeks ago, and I can just agree with what all you're saying.
There's definitely a greater demand for nutrients and especially magnesium.


In the past I vegged with ~1,2 EC (0,2 from the tap) under a 400MH - under my quantum boards I had to raise the EC to ~1,8 and magnesium to 90ppm and they still seem to be very hungry.
I think the more PAR and the lower your temperatures, the more you have to push the nutes (as some of you also explained).


It's very reassuring that I'm not alone with this problem and makes me confident to try to push my EC even more...


What ppm magnesium are you guys running?

I wrote this elsewhere, but it should of really gone in here

The VPD graphs I have seen, I have to presume, are plotting leaf temperature against RH.

If we think sodium, the leaf temperature could be higher than the surrounding air. You have seen a hot drink in a cold place steaming away.

If we look at leds, the leaf will be colder than the surrounding air, as it is basically sweating. Does the hot drink steam so much, when the air around it is hotter than the beverage.

K is a common enough deficiency. It's involvement with stomata opening, and thus plant cooling, is where we see it lacking. With the leaf extremities torching. Under led, I have heard people talk on N,P,Ca and mg deficiencies. All the main ones except for K.

These graphs of temp V RH are not telling us our VPD under led lights, in my opinion. I have just exploited the virtues of leds, and got my RH up into the magic zone, where I couldn't reach with my hid's. Plants hated it. Couldn't drink. Sat there draining every bit of feed from the fertigation, and stripping the Ca+mg cations from the coco to. Fertigating at ec 2.1 wasn't enough, because I couldn't get a second fertigation to them before the food run out. They would of been permanently wet through.


This is just this weeks thoughts on the subject, as I evolve my methods of led growing. While using mainstream examples of what else should work. My plants turned a huge corner when I dropped the RH, from omg that's shit, to ain't that lovely. With a 10% drop in RH. Though that might not be the only significant change, as I'm battling on a few fronts.

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I'm also thinking about root temperature. Where once people may of battled keeping temperatures down, they may now be looking towards inlet heaters. Hard to quantify into this thread at this point, but perhaps it's own thread is needed, to gather some data

I have noticed a K deficiency with my plants. I added MKP and it went away. But if I stopped adding it it comes back again. Still dialing it in though.

That's odd.. was it typical burning right at the edge? I really didn't expect to hear of a K problem. In my mind I'm formulating a new feed, and K was reduced to help Ca and mg find a place on my coco. It seems led growers have found every problem possible now. With the usual spread of results. Leaving only the requirement for 'more' as a common denominator. Though even that wasn't found by everybody.

I guess by your double trial that this wasn't at the end of flower, when K has other uses.

My brain hurts thinking how you were burning up with just leds and a typical K level. Such freak results are often excluded from trial results as anomalies, but coming from you, I have to listen.

f-e said:

That's odd.. was it typical burning right at the edge? I really didn't expect to hear of a K problem. In my mind I'm formulating a new feed, and K was reduced to help Ca and mg find a place on my coco. It seems led growers have found every problem possible now. With the usual spread of results. Leaving only the requirement for 'more' as a common denominator. Though even that wasn't found by everybody.

I guess by your double trial that this wasn't at the end of flower, when K has other uses.

My brain hurts thinking how you were burning up with just leds and a typical K level. Such freak results are often excluded from trial results as anomalies, but coming from you, I have to listen.

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I think you miss understood what i was saying. I had purple stems showing on the fans and stems. I added MKP and the new growth showed no purple. I added this for about a week and a half and then started getting the clawing on the leaves. So I backed off of the MKP and the purling started coming back.

This happened in flower and veg. When I added the MKP I also noticed thicker stronger stems.

I am still looking into how much MKP I need to add and when exactly is best.

Douglas.Curtis said:

Curious, who has a cool and dry flowering environment with their LEDs??

Cool and dry conditions suck for soil, since the microherd much prefers warmer days, but it's what I use with hydro. The transpiration rate is decently high. Normally, this high of a transpiration rate, combined with a full pH swing, allows me to keep the feed strength rather low.

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This guy. I just did a run at 19 day and as low as 15C nights I’m at about 30-40% RH and had a ts2000 going over a 150 gallon organic soil bed. I had no issues at all with feed except I thought fade set in a few days or week early... it turned out to be a really great finish though and regardless of slight yellowing earlier than expected the buds grew healthy and finished heavy and frosty.

I have a strong eye to keeping CEC as saturated with Ca and P as much as possible and I feed fish hydrolysate with fishbone (makes it high N and P) added to its mix as well as Rock dust and insect frass and/or plant meal (Cannabis,Dandelion, Yarrow, Nettle) as needed or just prior to key points of influence in plants life.

For example a small feed of fish on top of rock dusts and mixed plant meals at flip becomes available almost immediately in some respects but also via micro herd as stretch begins.
Even the ionically (is that a word?) available portions will be taken in by soil biota as well as the CEC absorbing some on its way to the roots so one can look at it as having an “incubation” of sorts before the plants increased needs make use of it.... beyond what is washed into the actual rhizosphere upon watering.. which is only once every day or two at peak production.
There’s a lot of clay in my soil and I rely on it to be able to hold some water even to the point of allowing top of soil to dry significantly at mid stretch and onset of stacking. As senescence sets in I begin extending dry cycles until it’s in a draught at least two days prior to cut.

If I keep feeding things like lacto b. or molasses or aloe and/or coconut every week I can keep that herd thriving until next application of feed may be needed say as stretch ends maybe I throw a little extra rock dust or some bat guano or bone meal with a little frass..
I usually only have to feed like that for a cycle or two and then I can do water only for next cycle or three if I wish depending on how much I feed during “hungry” rounds. I’m trying to keep heavier feeders in the hungry cycles and more sensitive stuff in the water only bits.
I pretty much always need to watch for Mag def and be ready to foliar with Epsom or throw some in the water barrel.

I also got a lot of improvement from very light use of Boron in the Rez once every three or four cycles.

For what it’s worth I live in a pretty cold dry place with very little organic matter in the soil so it’s likely the local microbes are adapted to lower temps and loving the huge buffet of food in my dirt... or maybe I just get a little luckier every run

I will say that any plants under LED that get even a little rootbound (I have a solo cup garden to be ashamed of for veg...) show deficiencies right away... usually Mag or K in my case but I have also noticed P def shows up pretty frequently too... lol I’m a neglectful bastard to my poor solo cup plants... they get pretty upset after a couple weeks of surviving off that little cup of soil...

f-e said:

That's odd.. was it typical burning right at the edge? I really didn't expect to hear of a K problem. In my mind I'm formulating a new feed, and K was reduced to help Ca and mg find a place on my coco. It seems led growers have found every problem possible now. With the usual spread of results. Leaving only the requirement for 'more' as a common denominator. Though even that wasn't found by everybody.

I guess by your double trial that this wasn't at the end of flower, when K has other uses.

My brain hurts thinking how you were burning up with just leds and a typical K level. Such freak results are often excluded from trial results as anomalies, but coming from you, I have to listen.

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I’m just guessing a bit here but if PAR is increased so too should the amount of N and all it’s co-dependent nutrients; poor choice of words perhaps but I meant everything involved in N metabolism for photosynthesis. Ca Mag iron and I think K are needed to make chlorophyll if my stoned ass brain is making any sense and B is helpful to the process too iirc. I may be foggy on the exact elements and process but basically we will need to provide for increased consumption of the components of chlorophyll and the catalysts enzymes proteins and whatever else is used for RAPID growth.
Once that is accounted for it’s got to be about roots growing fast and large enough to access all that extra food at a rate of concentration that feeds accelerated growth but won’t burn the roots.

Manipulating how much they drink with RH and temp is a good way to get them eating constantly on that koolaid but in a rootbound environment I think it will always be a much finer balancing act.
Lol but sometimes I get real high and lot of words just kinda pour out.. maybe this is that.
Hope I’m making some sort of sense to someone.

Edit: please expound on other uses for K at end of flower.. do you mean to aid in maturation and add weight or are you touching on the cigar industries use of K to manipulate burn rate and ash colour?

Red stems can be difficult to diagnose. Virtually any stress can cause it. If the fix is PK, but burn's them, perhaps the substrate is a bit hot to begin with. My names sake, f-e, causes P deficiency. Which shows as red stems. The leaf stems seem to pick up the colour as if sprayed from below. Gradually turning the entire stem red. Just as K would if pushed out by perhaps Ca or mg. I was scanning your posts to see the K problem you're having, and saw you add Ca and have a low run-off percentage. That was back in 2015 though.

Oh.. I missed your posts YukonKronic. Very good posts to. With more K deficiencies. Though under the extreme circumstances of not giving them shit.

I wasn't eluding to anything. I was pondering on the plants age at the time the deficiency was showing. I'm still looking for pics, but just red stems won't get me preaching that it's K

great thread.

Im about to start using an LED for the first time. An Illuminar Il8, which is supposed to compete with the new fluence lights.

From what I was told by the sales rep, is you want to keep the lights as close to the canopy as possible, but reading this thread it seems that is asking for problems.
So you guys are running these as high or higher over the canopy than DE HPS'? Ive been wondering if its better to run them at 100% and put them higher or dim them down and try to get them as close as possible without issues.
Will actually be using a DE HPS along with the LED for now. Thought It would be casting a shadow over the canopy due to being higher than the LED but if I could run them at a similar height that would fix that issue.

headees said:

great thread.

Im about to start using an LED for the first time. An Illuminar Il8, which is supposed to compete with the new fluence lights.

From what I was told by the sales rep, is you want to keep the lights as close to the canopy as possible, but reading this thread it seems that is asking for problems.
So you guys are running these as high or higher over the canopy than DE HPS'? Ive been wondering if its better to run them at 100% and put them higher or dim them down and try to get them as close as possible without issues.
Will actually be using a DE HPS along with the LED for now. Thought It would be casting a shadow over the canopy due to being higher than the LED but if I could run them at a similar height that would fix that issue.

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Not all LEDs are the same. I have some that I can run within 10 inches of the plants or closer when they are established. But I have others that will kill the plant when that close. You need to test the light out to know how close you can get it to the plants.

Ok that makes sense thanks. I know that these lights are very powerful much like the fluence spyder 2p and are supposed to dim them. I’d rather put it higher and run it at 100% and get some overlapping light. But This is all new to me so I guess I will have to see what works the hard way

I would mount it higher and brighter, rather than lower and dimmer, when trying to achieve the same canopy illumination. There are obvious concerns regarding heat and power usage, but more lumens in the area is a good thing. Some of the extra one's will be bouncing around for a bit before hitting the canopy at different angles, leading to a greater penetration. The greater gain comes from the lights bigger footprint though. It's finger math to see a 12" panel that's great at 6" away, can only light an area a few inches larger than 12"

Circumstance varies.


If they look a little ill, check the run-off. If it's low, they have eaten everything. That might be the best guide.

Boy o boy, I sure had trouble in my veg space with some quantem boards. I almost lost my moms and dont have plants to fill my flower space. I dont know if the lights were too close or what was the haps but Its back to t-5's and hps for veg.
I tried cal mag, and more food but everything under those boards hated it in veg. Two weeks later stuffs back to norm and looking healthy.
My LED flower room is doing well at half the power ,all the weight

My guess is to much light and not enough roots. b Try running the lights higher till the roots develop more to support that much light.