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need help identifying growth problem

Posted by laurichj (My Page) on
Thu, Feb 5, 09 at 14:00

I've got some plants that are initially growing great, but when the second set of full leaves come in they'll be very yellow. Eventually (2-3 weeks) they'll start developing white patches and the plant will stop growing.

My setup is:

- maxigro nutrients, no EC meter but mixed to the "proper" strength, I've tried as little as 50% with the same results.
- drip system, on 15m off 15m
- 400w HPS a couple feet above the tops (~2500 foot-candles at the plants)
- 24h light since it's all vegging
- PH is ~6, maybe 5.8-6.0. I'm using the General Hydro color based test kit, so it's not very precise.

I've had the problem with tomatoes and green beans, but everything else seems to be fine: a few types of greens, carrots, parsnip, and okra. I also have a bell pepper that looks fine, but its a small plant and barely has the second set of leaves. I have two watermelons that are yellower than they should be, but they're growing fine.

The older leaves will pretty much stay green. The veins in the leaves will be pretty much equally yellow. I've added some Iron recently thinking that might be it, but I'm not really sure and it's too early to tell if that's the problem.

Some pictures can be seen at:

Any help will be much appreciated, thanks!

Follow-Up Postings:

RE: need help identifying growth problem

Not sure what your issue is, but I had the same symptoms on my plants, tomato and green bean. I do DW and while removing the net pot from the bucket it was in, I noticed that the roots were coated with the powder from the grow rocks (I must not have rinsed them well enough). The roots were so coated, that they were completely brown.

I washed the roots and media off with room temperature water. I then changed out my nutrients and they came back just fine.

RE: need help identifying growth problem

Off the top of my head, it looks like your plants are light starved. Tomatoes will drop their first two pair of "real" leaves once the plant begins the "vegetative" stage, but it looks like yours are readying to drop them all!

I don't use supplemental lighting, so I'll not offer any advise there. Any chance of getting your plants into a sunny location for a while to see if that's the problem?

RE: need help identifying growth problem

I can't imagine that they're light starved with a 400w light on them.

I wouldn't dream of running the light all the time though... plants need rest. Drop them down to 16 hours on, 8 hours off, run off a timer. Plants, especially higher order ones, need the darkness to perform many of their daily tasks.

I'm not sure that's what the problem is, but that'll be a step in the right direction. Even during vegetative growth you need to let your plants sleep.

RE: need help identifying growth problem

What is your medium?
how often do you change your solution?
definitely cut the light cycle as gary pointed out.
Also, HPS isn't the best bulb for vegetative growth unless your buld was built to include the bluer spectrum.
Oh! how old is the bulb?

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