hps vs. mh yellowing fan leaves in bloom issues

So I have been working on my indoor grow for two years. On a budget of course. When I first started i received a free 250w MH fixture so I used it for blooming. Free is free and it worked. Decent buds. My 8wk indica took a little longer to finish 10-11 weeks. Which was fine. The bud was good and no real complaints with the MH. I have since upgraded to a 400w HPS. Btw my grow tent is hxwxd = 5'x4'x2'. I have come across and issue that has plagued me for a while and I think I've narrowed it down to the lighting. Under the MH no issues. Under the HPS, around 3 weeks into bloom, the fan leaves from top to bottom begin to yellow. The rate is faster at the bottom, but it affects the entire plant new and old leaves. The green fades to a yellow, then death of the fan leaves. This obviously begins to affect the bud and I am forced to harves early. I've tried switching nutes, soil, water to no avail. The issue crops up every grow on every plant. The light fixture is about 16" above the tops of the plants. Temps range from 63-87 with 55% humidity. I'm using 2g pots right now, I even have a plant in a 3gal and same issue.

Is this a light bleaching issue? I'm not sure how else to describe without pictures. I'll get those asap. But I mean its straight forward, the plants and leaves look healthy and lush during veg then the leaves begin to lose the green and go yellow on me 2-3 weeks into bloom which is way too early.

Any suggestions are worth their weight in gold so please give me ideas.

I've noticed the same issue, but I've only had experience with 600 and 1000 watt HID systems. Always after switching to the HPS and 12/12 after a number of weeks the top to bottom yellowing you described sets in.

Also despite losing all of my fan leaves I always let the bud finish, the "bud leaves" on my plants never die just the fan leaves. I once watched a truly massive plant grow "buds on sticks" for four weeks. They swelled a lot in the last two weeks, totally worth leaving up there. On the down side the bud did come out fluffy, but still 8.8 Oz from the one plant. Looked like a pound though.

It could be that I've never bought a "grow" bulb, but always used the cheap bulb that comes with the light.

Also I eagerly await others suggestions - this problem frustrates me.

ok heres my example/suggestion, I just switched my 400 watt mh out and put the hps bulb in yesterday. I left the timer the same though, so now they are vegging still but under the different light- getting used to it, and I will check them pretty soon, every few hours. for whatever reason the hps seems brighter so I will make sure my watering is enough and that they grow for a week or 2 more at least before I will change the schedule. practice vegging with the hps sometimes if you haven't already

I've vegged under HPS, but the problem has never cropped up then. Tends to make the plant stretch more though.

It does put out more light, but I don't think normal light problems take three weeks to manifest.

Sub said:

It could be that I've never bought a "grow" bulb, but always used the cheap bulb that comes with the light..

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Your on to something there I think. Anyone have a good suggestion for a 400W HPS grow bulb. That might be part of the issue. What you describe is exactly what I have. Sticks with buds, but see the leaves among the buds start to yellow as well and those are hardest to remove. I dont like seeing those start to yellow. What I might do is take something like a 100W MH and run it for a few hours during the same time as the HPS and see if the additional blue helps. But then I'm up to using 500W which is not what I'd prefer.

The lightblub i'm using is just a 400HPS "Venture Lighting" brand.

hydrosoil78 said:

ok heres my example/suggestion, I just switched my 400 watt mh out and put the hps bulb in yesterday.

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This would work except I have 2 tents, one for veg and one for bloom. Now I have a mh bulb that would work, its one of those HPS compatible MH bulbs. I could swap it in for a while for the extra blue, Eh i can't even do that because I dont bloom all at the same time. I still think my best bet would be to add soem blue spectrum to the 400w HPS. Should I go with a 100MH or just use some floro lights? maybe a CFL?

There's another thing it could definitely be.

If you water or soil is not perfect (rarely is) then over time the soil PH will change to a less desirable level.

For example if your soil has many organic components over time your soil may become too acidic due to decomposition in the soil. This does create nutrients for your plant but also over time makes the soil more acidic than it started, and over a long period may eventually cause nutrient lockout.

If your water is not perfect it could also be throwing things off over time. Around here my tap water PH is over 8.5 which over time will make the soil PH too basic and eventually cause lockout.

Lastly tap water can have additives that cause lockout over time, such as having a high concentration of dissolved minerals in your water. If your tap water is hooked up to a water softener over time this can do the same thing, causing minerals to build up in the soil creating lockout.

So really there's like a complex interrelated system that you have not looked into yet - your soil/water interaction cycle.

I think this could be whats causing it. In your case switching from a 250W output to a 400W output is going to speed up how quickly your plant uses water/nutrients. This would accelerate any imbalance that might happen over time in your system, as the more you water the plant the more the system goes out of balance.

Also if you find you have basic water (like me) that can be a sign of heavy mineral content. Just filtering my tap water brings it down to a PH of 7.2 which is much less likely to throw off my soil PH over time. You should probably get chemical PH testing kit to check your water and soil.

To check soil PH simple take some soil from your plants container and mix it 50/50 with water and let that sit for a while. 20+ minutes later filter that watery soil through a paper towel or coffee filter so that you can PH test the water.(which is your soil PH)

Edit - You can check for heavy mineral content in your water with an EC meter, it's the last thing I need personally.

Thanks for the info, however I have already gone down this route with many trials of water and soil. I'm purely organic soil with a weak soil feed of organics as well. I did a test of half my plants rain water half my plants tap and both had same results. The tap water tends to be hard with a ph of 7.0. The peat in my soil mix will take care of an over abundance of hardness anyhow. The rainwater in my area is about a 6.8. A tad bit acidic, but not that bad. I also have lime in my organic mix to handle any harsh ph swings to the acid side as the organic materials break down. Now I am fully aware that organic soil is a diamond in the rough approach until you work out the kinks, but I got a pretty decent recipe off here a while back. It has shown good results in the past. I'll read your post a few times and see if it sparks any lightbulb with what I'm doing, but I think the tests I've done with the 2 water types would show something different if it was a water issue. I have doin soil readings and water runoff readings ranging from 6.4-6.8 depending on the age of the plant.

Well all those numbers seem pretty good IMO.

I've been down the same roads myself and all my numbers look good yet I still get the same yellowing you refer to so hopefully someone can enlighten us. I also have an organic soil mix that I'm using, but this round is the first. Same symptoms at the same time as when I used chemical fertilizers.



My current theory is that under HPS the rate of bud development is putting demands on the plant that the root mass is failing to keep up with. IE the amount of growth happening under the HPS is literally using more nutrients than the plant can take in, so it cannibalizes the leaves to make ends meet.

The theory is dependent upon a couple of assumptions - 1. Rapid root development occurs during the start of flowering to support the buds + stretch. 2. Slow draining soil prevents rapid root development. 3. Slow root development combined with rapid floral/bud development leads to a resource shortfall in the plant.

What I plan to try next grow is soil than drains so well that I have to water every other day. Right now I water once every four or five days, although it is getting more frequent now that there are some decent size buds to support.

If the issue was lighting, everyone who runs hps would have this issue, but they don't. Sounds like your issue is lack of Nitrogen or your pH is off which is causing nutrient availability issues. I would suggest that you add some fulvic acids to your feed schedule which will open up the nutrient availability range. Adding a small amount of chemical nutes to your schedule wouldn't be a bad idea either.

Alright well I'm goign to try and mix some HPS and some blue light. What I might do is go back to the 250W MH, and then find a low watt HPS for the additional red. My guess is as the same as yours. The HPS is taxing the plant biology too much that it can't keep up hence the cannibalistic nature. I'm goign to see if I can get a 100-200W HPS to combine with the 250W MH.

I will also try keeping the 400W HPS and add the 100W MH I have as well and compare results. I just think that this second option might still present the same issue of overtaxing the plants.

PJ Diaz said:

If the issue was lighting, everyone who runs hps would have this issue, but they don't.

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I agree with you, however there is more than just light involved. You can use 1000W HPS light with a 1g pot plant and I bet you would have issues. What I'm trying to do is with my setup, size ventilation soil ambient temps etc., is find the optimum lighting, wattage and color temp. I have supplemented organic nitrogen fertilizer (fish based) and haven't seen any improvements. Adding chemical nutes, form what I've heard, will affect the organics that have developed in the soil. Once organic stay organic. Am I wrong?

I've tried soil changes, larger pots, additional nitrogen based ferts (organic), different water to no avail. I've tried raising/lower lights, more ventilation. I'm at my wits end with this thing. And my only anchor is that I didn't have this issue in bloom under MH.

Thanks to everyone so far with the food for thoughts keep up the brainstorming.

P.S. I have started using cloth pots to help with a better root ball hoping that helps.

You can use a 1000w hps on a one gallon plant no problem. The plant would love it. It would almost feel like it was outside under the sun. If you're really worried about more blue light, just buy a hps lamp with extra blue, like the Digulux.

With organic nutes, they aren't always readily available until they get broken down by soil organisms. I'm sure it's debatable, but IMO you get the best of both worlds by going 90% organic and incorporating a small amount of chem notes.

If you are really worried about chem nutes screwing up your organic soil, then try folier feeding with half strength chem nutes. Folier feeding hits the plant immediately and you should see improvement in days.

In terms of organic, as I said before I'd highly suggest adding fulvic acid in your feed, which will make the pH nute range more widely available to your plants. Liquid Karma is great for this, and also includes many micro nutes and vitamins.

I'd also suggest switching from soil to coco. You'll be glad you did.

Now there we go. I was looking for hps lamp suggestion. I will look into Digulux. Thanks!!

Yes with my organic soil I let it back for about 4 wks before use.

I may stay away from folier feeding for now to avoid any burn issues. Just to keep that out of the equation. Dont trust myself.

I already add small amount of humic acid when I hydrate soil mix before putting it outside to bake. What are you recommendations humic/water. I use 1tsp/gal of water.

If you're worried about burning with foliar, just go 1/4 strength.

Humic acid is great, but I'm talking about fulvic acid, which is like super humic acids. They can't put fulvic on the label of Instant Karma, but it's in there.

I really don't think your issue is lighting, but I use Digilux lamps, and they will definitely help in other ways.

Thanks PJ for the help so far, and everyone else as well. I'll take another look at ph with my next set of plants. Changed the soil yet again. I'm almost positive its not a ph issue. Might be a nutrient issue though not sure. Oh well back to the labs. I'll do the veg based foliar feed tonight and report back on the progress/results in a few days.

Just ordered this http://www.amazon.com/gp/product/B00286SR1S/ref=oh_details_o00_s00_i00
I didn't plan on getting all three, but the LK by itself was 13$ so an extra 5$ for all three seemed like a better buy. Also if you use eBay they have the LK for under 8$ shipped.

Can't wait to see if humic/fulvic acid will solve/help my problem. I have noticed light feeding with chemical nutrients helps slow the progression of the yellowing, but conversely too much makes it worse.

Sounds like a nute problem.
MH is perfect for vegging and HPS for flowering.
You can use HPS for vegging it would just be a more dense veg cycle but MH is not recommended for budding.

Sub said:

Just ordered this http://www.amazon.com/gp/product/B00286SR1S/ref=oh_details_o00_s00_i00
I didn't plan on getting all three, but the LK by itself was 13$ so an extra 5$ for all three seemed like a better buy. Also if you use eBay they have the LK for under 8$ shipped.

Can't wait to see if humic/fulvic acid will solve/help my problem. I have noticed light feeding with chemical nutrients helps slow the progression of the yellowing, but conversely too much makes it worse.

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I use pure blend pro with liquid karma for flowering. It's great stuff and the girls are happy campers being fed it.