Why is my yield so low?

I run an ebb & flow sog/scrog system under 2 1,000 watt HPS lights(bought them used but they told me were used only ~60 days or so). I have 540 CFM fan pulling air through both hoods and into the attic. I was attempting to put the lights lower to increase density but have had multiple problems with heat and light stress when too close to the canopy. I now have the lights about 1.5-2 feet away from the tops of the plants. I have a small 4 inch can fan blowing in intake when the room gets above 78 degrees. The room stays 70-79 during both light and dark periods with a RH of 40-60%. I put in a small heater to avoid temperature dips when the light is off. I grow in rockwool 6x6 cubes and flood and drain as the plants need it being sure to check my res temps, ppm, and ph always have ppm 1500-1900 and ph of 5.65. My genetics come from a reputable dispensary (Harborside) and I grow high yielding strains like atomic northern lights, grand-daddy purple, etc. My only noticeable issues have been light/heat stress and small outbreak of white flies which is being controlled by fly paper. I've been getting really low yields ~1/4 ounce per plant which is way lower than I expected. Does anyone have any tips I can use to increase my yield?

Album of room: http://imgur.com/a/yEq3b (sorry for duplicates!)

Can we see some pics of your plants?

that is low for sure, especially with the amount of watts u have, now if it was hps then i would worry i dont no about hids !!!!! spectrum n all that, as the blue end is for veg n red for flower or vice versa either way hps covers both these very well, what r hids exacly as re there spectrum output ? only say coz u av everythinkelse honed to a degree as kit goes,, i am sure u use a good quality soil n ph regulary ! u do say theres no variables in temps at lights out now if thats the case then this needs addressing as in the real world they will go through roughly 10f drop at night time so u do need some degree of night n day temps for ya plant to get to grips with how it would b in nature,, so other than that issue n hids spectrum range as they may b better for veg but not as efficient in flower its hard to say y this is !!! how long do u veg for and at what size r ya plants when u go to 12/12 ?

Heat sounds kind of high. I'd lose the heater - the temps could go down to 60 in lights off and no problem. Those heaters don't have reliable thermostats - you could be getting high heat in there in dark time. That's why I have a thermometer that registers highs and lows over last 24 hrs.

just 6x6 cubes? i dont run hydro, so i might have the wrong idea,but you need more root space than that...ever watch the video tutorial " i grow chronic" on youtube, gives a nice idea of what you need to be doing.maybe your not using the correct flowering nutrients...i dunno.

whats your size room? for sog is better to use mid intensity lighting throughout ,, like instead of 2 -1000w .. 3- 600w would give you more light and more distribution and also you could bring the light closer to avoid stretching... also try bringing your ph to 5.8... and keep your water cool.. below 70f.. also the biggest thing your forgetting if you wanna really yield is co2.. good luck

Vick - Yep but I don't have any atm I'm gonna take some tonight and hopefully post up tomorrow, but be warned one of my trays is badly burned by heat/light stress early on, the other trays look pretty good, I'll try and take quite a few but would you be more interested in room pics? Whole plant pics? Tray pics? Canopy pics? Just so I have an ideal what your looking for.

f1bud - Oops sorry they actually are Hortilux HPS bulbs (sorry was in a rush when typing my first post). I'm actually not using any soil its completely hydro with all rockwool (I used to use coco mats under the cubes for root expansion but trial and error tells me its unneccessary and usually causes root rot.) Yep I ph with an oakton ph meter, it's a good $120 one. And yep I let my reservoir sit for a bout 5 minutes while the water circulates to make sure the pH is constant throughtout the reservoir. There is a slight temp drop thats roughly 9 degrees or so at the plant canopy, before the temps would range 20-30 degrees between lights on/off but has since been corrected with the heater.

Illegal - Actually I was having issues with it getting too cold at night especially in the winter (I've seen it drop to 50 degrees which shocked some of the plants) Also the heater is set to a timer to keep it coming on only when the lights are off. Yes I have a couple thermostats and RH meters around the room and they measure 24 hr high/low. The temps I posted are the recent 24 hr high/low since fixing my previous temp issue.

Smoke - I have tried to grow with coco-mats under the rockwool cubes but even with no temp issues they never really expanded to the coco, usually the coco mats would retain too much water on a flood and cause further root rot issues. I'm also following advance nutrients feeding guideline pretty much to the letter.

Treme - The room is about 8x10 feet but the grow area is 4x8 with 4 2x4 trays. Yes I was actually thinking 3 600W would be more efficient but I kind of in a hole now and I have 3 1000W ballasts and lights. My water was actually very cold for a while 55 degrees or so and this caused root shock and root rot, I've since changed res temps to about 75 degrees and my plants water uptake has improved dramatically. Yes I agree I might need CO2 but do you really believe this to be the limiting factor? Even without CO2 I believe I should be yielding more than 1/4 oz per plant.

Thanks for the suggestions, I'll try to keep updating regularly, keep the tips coming!!

How many plants? You should be hitting 2lbs total. If not, it's lack of root space or problems with irrigation timing. Only used hydroton myself so can't help with that.

1500-1900 ppm seems kinda high to me. What nutrients are you using? Technaflora, AN, Etc??? How many flood/drain cycles are you running daily and how long. How long is your Veg period? I would say veg for 8 weeks, run 75% strenth on your nutrients ( manufacture suggests way too much ) 24/0 light cycle, flood and drain every 3 hours for 15 mins, then see if that doesnt help your yield

cues said:

How many plants? You should be hitting 2lbs total. If not, it's lack of root space or problems with irrigation timing. Only used hydroton myself so can't help with that.

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I've been toying with the how many plants and been adding accordingly. Right now I have about 36 flowering. I've been adjusting each tray to get a good canopy that maximizes light penetration and have found that 10 per 2x4 tray has been optimal for me.. so far. Root space seems okay as I only veg for a maximum of 3.5 weeks and generally around 2 weeks. The plants end up about 1-1.5 ft tall when entering flower. I was actually considering filling my trays with hydroton to surround the rockwool cubes as I've seen in the 'I Grow Chronic' series on youtube but I personally know a few people that only use rockwool and are getting much better results than mine. Another thing I've noticed is that sometimes my plants can go 3-4 days without needing a water (I know because their weight and experience with watering too frequently and root rot issues.) and I frequently read that some people are watering multiple times per day, IDK if this is isolated or general consensus with ebb and flows. Thanks for the suggestions.

SALTWATERKUSH said:

1500-1900 ppm seems kinda high to me. What nutrients are you using? Technaflora, AN, Etc??? How many flood/drain cycles are you running daily and how long. How long is your Veg period? I would say veg for 8 weeks, run 75% strenth on your nutrients ( manufacture suggests way too much ) 24/0 light cycle, flood and drain every 3 hours for 15 mins, then see if that doesnt help your yield

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I've been using AN exclusively with some great white shark and microbe brew to help with the root zone. Been adding some B vitamins and big bud (which isn't working as advertised : p). I only flood them for less than 5 minutes and every 2-4 days when they feel like they're getting light. My rockwool is pargro quickdrain (recommended by my grow shop to aid with drainage issues and to maximize waterings). I'll flood each table about an inch and let them soak up what they need. Harborside told me my strains are heavy feeders and can take a lot of abuse and I believe they are only showing minor burn on the plants that are doing well; but maybe a nutrient reduction is what I need. Thanks.

I would keep the medium the same type but more of it. I seem to remember you can buy it in balls?? 36-6" cubes is only 9 ft square of rootzone. Not enough for 2KW. Just tip some of those in. Not sure about Hydroton. Surely the roots would just grow into it then drought out.
I flood my hydroton at 4 hr intervals but think that would be way too much for rockwool. Are you keeping light out of the rootzone and res? Any signs of pythium? If you're only pulling 9 or 10 zips something is wrong. I pull about 17 off a 600w with no real effort.

I've grown in rockwool 4 a few years now
And I think u should b watering alot more
im using flood and drain buckets and I feed every hour
and every hour when the light is off
2-3 days seems a very long time ?

2-3 days... ?

vaseline68 said:

I've been toying with the how many plants and been adding accordingly. Right now I have about 36 flowering. I've been adjusting each tray to get a good canopy that maximizes light penetration and have found that 10 per 2x4 tray has been optimal for me.. so far. Root space seems okay as I only veg for a maximum of 3.5 weeks and generally around 2 weeks. The plants end up about 1-1.5 ft tall when entering flower. I was actually considering filling my trays with hydroton to surround the rockwool cubes as I've seen in the 'I Grow Chronic' series on youtube but I personally know a few people that only use rockwool and are getting much better results than mine. Another thing I've noticed is that sometimes my plants can go 3-4 days without needing a water (I know because their weight and experience with watering too frequently and root rot issues.) and I frequently read that some people are watering multiple times per day, IDK if this is isolated or general consensus with ebb and flows. Thanks for the suggestions.

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I ment 3-4 days is 2 long
ur rockwool should b damp at all times
but not drenched

Has to be one of a few things:

1. Your not vegging the plants long enough and when you start flowering, the plants are small and the root system is not fully developed.......or

2. Poor overall health will stunt plants and greatly impact yield.......or

3. The lights are putting out very shitty lumens and the plants don't have then energy to produce well.......or

4. A bunch of other possibilities like bug infestations, too hot or cold, plant genetic issues, etc.


Pictures of plants at various stages would be helpful. While rereading this all, my unprofessional guess is stunted roots caused by your poor watering cycle. Cubes need to be water numerous times each day whether you think they need it or not, not once every 3-4 days.

Here ya go. https://www.rollitup.org/grow-journals/429438-dyna-gro-vs-advanced-nutrients.html

Read through this and come back and ask questions.

Album added here : http://imgur.com/a/yEq3b

IN33D - Yup 2-3 days when they start to feel kinda light, if sooner they start looking kinda sad. I've tried watering every my first time and it killed everything with root rot. Idk if temps were the issue but I believe the plants that aren't heat stressed look decent but I'll let you be the judge.

Jay - Ya I leave them damp but generally after flooding they stay heavy for at minimum 36 hours. Depending on the plant size.

SSHZ - I did mention I'm having a minor white fly problem which is being controlled by the fly paper but could they be the major reason I'm yielding so low?

10-30 - Thx I'm gonna have a go at it now.

Thx everyone keep the critique up!

U need 2 water more often with less water
r u watering by hand ?

Jay - I was for a bit, roughly 500 ml per watering but its become tedious to check every plant and the day 23 tray I've been flooding with decent results.