Tricky PH question

Hey, so a lot of different material tells you to use different PH levels. So I wanted to find out what is the best one. From the research so far, these are the reasons:

1. Different plants use nutrients at various ph levels
2. depending on whenever you use soil or hydro the ph should be different. ph for soil systems should be 6.0-6.5 and hydro should be 5.5-6.0

I guess the reason the soil PH should be higher is due to the soil lowering it to the needs of the plant. However, how do you factor in the soil ph levels? Does the formula of (ph = water PH level -/+ soil PH) work? Would it be safe to say that ph run off for soil should be around 5.5-6.0? What is the PH level that bud best absorbs nurtiets at? Help me out so I can :rasta:

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Originally Posted by uncleweed

1. Different plants use nutrients at various ph levels

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True. Cactus needs a different ph than cannabis. However, Cannabis prefers a slightly acidic environment to properly function, but you must still keep ph within cannabis' acceptable range. Shoot for the middle of the road, and all should be fine.

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Originally Posted by uncleweed

2. depending on whenever you use soil or hydro the ph should be different. ph for soil systems should be 6.0-6.5 and hydro should be 5.5-6.0

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I stick with 6.3 to 6.8ish for soil grows. Not sure about hydro or coco, as I defer all those specs to those that use them daily.

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Originally Posted by uncleweed

I guess the reason the soil PH should be higher is due to the soil lowering it to the needs of the plant.

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No, not really. Container soils are usually buffered with something (lime, gypsum, sulfates...) to raise ph to an approximatelly neutral 7.0 or so. As the buffering capabilities of the buffer fade with time, ph will take a dive. Each potting mix has it's own buffering capabilities, and some brands are buffered at different levels for different applications. Composts and mulches might or might not be buffered at all, and the lower (unbuffered) ph in those ammendments can kill a plant. (use the right tool for the job)

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Originally Posted by uncleweed

However, how do you factor in the soil ph levels? Does the formula of (ph = water PH level -/+ soil PH) work? Would it be safe to say that ph run off for soil should be around 5.5-6.0?

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Doesn't really work that way. Each garden is dfferent, as are the soils, soilless mixes, water and nutrients. For instance...if ammending water, it would take me around twice as much PO2 (a weak phosphoric acid) than if I were to use PO4 (a stronger phosphoric acid) Same thing with soil buffering agents. Buffering capabilities of brand A are likely different than brand B's capabilities, and it is possible they are buffering with different needs in mind. Since there are different buffering agents used in the industry, (lime, gypsum, sulfates...) likely each brand will be slightly different at interacting with your specific nutrients and water. Runoff should be in the 6.3ish to 6.8ish range for container soil. Any lower and you risk nutrient lockout. (for container gardening with soil or soilless)
I monitor runoff and ammend my water if runoff isn't within a 6.2 to 6.5 range. Bad idea to ammend soil ph (mixing in additional buffers) when plant is actively growing/flowering. Best to ammend the water to control ph.

The best way to determine your runoff ph is to use a ph pen. On nutrient day, check runoff ph. Then, on a watering (non nutrient) day, check the plain waters' runoff ph. Color-coded test strips and aquarium test kits are no good for this, as the tinting of the runoff skews the color-coded results.

Any of this make sence...? Time for some coffee. :thumbsup:

:thumbsup:...

Ok, so here is a follow up question.

If I am putting in water/nutes at 6.3 ph, and the run off is at 5.3, should I raise my water/nutes ph level to 7.3? Does this work if offset was reversed?

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Originally Posted by uncleweed

Ok, so here is a follow up question.

If I am putting in water/nutes at 6.3 ph, and the run off is at 5.3, should I raise my water/nutes ph level to 7.3? Does this work if offset was reversed?

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Ok, so here's a follow-up question's follow-up, lol.
What are you using to test the runoff? A lot hinges on it being an accurate number. If you are giving us color-coded results, we may be giving you the wrong advise.

But to answer your question...if you are putting in at 6.3 and it comes out at 5.3...your mix is buffered more twords a mulch/compost than a potting mix.
If it is buffered at 6.0 or lower, I doubt lowering your water ph will work immediatelly. The buffer(s) in your potting mix will still fight to bring down your ph.

What potting mix are you using, and did you add any ammendments?
Do you have access to a 'normal' potting soil for a transplant?

rusty,

thanks for your answer. So far I don't have this problem, but I wanted to find out for my overall enlightement.

So what you are saying, is even if I raise the PH up, the buffer will act strongly against it and still lower it to 5.3?

So would there be any alternatives other than re-potting in new soil?

Thanks again