Is ph up and down needed for soil grows?

a senile fungus · Feb 17, 2015

Sativied said:
Maybe, not with any certainty though. I heard often dry soil increases EC/ppm (which then yes would affect ph too). Ca for example depends a lot on water uptake, K's job is to enter the plant and suck up water (simply put). Moisture content, water uptake, influences nutrient uptake, while nutrient uptake influences water uptake and affects pH. It's all connected, it's what people refer to when they say the plant will regulate it itself. Since you do not have full control like in hydro, it's often better to let the plant do it then try to steer ph in soil.

Maybe I was confusing EC and pH, embarrassing as I've taken chem classes and have a general understanding.

Yes, as moisture content in soil decreases, the EC of the remaining water will increase. Increased EC in that water would equate to decrease in pH.

All depending on the alkalinity of the H2O source of course...

But like you said, levels are different all over the soil. Not to mention, because the roots themselves are releasing H+ and OH- that the pH of the medium in the area directly surrounding roots is different from the pH say 2-3mm away.

Good stuff, thanks for the correction.

Sativied · Feb 17, 2015

a senile fungus said:
Maybe I was confusing EC and pH, embarrassing as I've taken chem classes and have a general understanding.

Maybe it comes down to the same situation just from a different angle, it works both ways.

a senile fungus said:
But like you said, levels are different all over the soil. Not to mention, because the roots themselves are releasing H+ and OH- that the pH of the medium in the area directly surrounding roots is different from the pH say 2-3mm away.

Which also means you can't get a reliable measurement. So the data is not reliable, the control method is not reliable, and the outcome is not reliable, and not reliably verifiable. On the other hand, using the "pour through method" you can still get an indication to see at least if it's not far off (pH and ec/ppm : http://www.ces.ncsu.edu/depts/hort/floriculture/Florex/PourThru Handout 123s.pdf )

If it is, it usually is because of miss-fertilizing. Another common reason (for ph drop during flowering and yellowing...) is similar, the lime buffer ran out influencing the CEC (cation exchange capacity).

For many soils, the CEC is dependent upon the pH of the soil. This is due mostly to the Hofmeister series (lyotrophic series), which describes the relative strength of various cations' adsorption to colloids, and is generally as follows:

Al3+ > H+ > Ca2+ > Mg2+ > K+ = NH4+ > Na+

As soil acidity increases (pH decreases), more H+ ions are attached to the colloids. They have pushed the other cations from the colloids and into the soil water solution. Inversely, when soils become more basic (pH increases), the available cations in solution decreases because there are fewer H+ ions to push cations into the soil solution from the colloids (CEC increases). (from wiki)

That's related to how we used to 'control' the pH outdoors in dutch soil, add lime/marl to make the soil "sweeter". Raise it to 7-ish from the 6-ish it's usually is, and let it decrease slightly throughout the cycle.

Another example of how nutrient availability influences pH:

Closely related to cation-exchange capacity is the base saturation, which is the fraction of exchangeable cations that are base cations (Ca, Mg, K and Na). It can be expressed as a percentage, and called percent base saturation. The higher the amount of exchangeable base cations, the more acidity can be neutralised in the short time perspective. Thus, a soil with high cation-exchange capacity takes longer time to acidify (as well as to recover from an acidified status) than a soil with a low cation-exchange capacity (assuming similar base saturations). A rain, with its load of acidic hydrogen ions, upon a soil that has a high CEC will be quickly returned (buffered) to its original pH in a very short time. A rain on a low CEC soil, such as in the Amazon Basin with its acid soils, will not be restored and the pH will drop sharply and remain there for a relatively long time.

undercovergrow · Feb 17, 2015

Sativied said:
Google Mulder's chart and nutrient antagonism.

Controlling PPM doesn't really apply to soil, but as someone pointed out it can still be useful to give an indication. If you don't overfertilize there's usually no need to even measure ppm though.

Whether pH matters in soil is not an opinion, it either does or it doesn't. And it sure does, but it's a wide range which in combination with normal fluctuations and variation of ph level throughout the soil makes it unnecessary to control. It often leads to more problems. If you want pH control grow hydro. At most controlling it matters if the tap water is too high by itself, or after miss-fertilizing (giving too much of everything or too much of one or more elements) but if the tap is high and the ph drops from over-fertilizing one can simply give water only for a while. The uptake of some elements increases pH, others cause it to drop.

View attachment 3353450 <-not a dick pic mods.
Note the H+ and the OH- the plant releases to exchange with a useful element. The pH is a measure of the molar concentration of hydrogen ions.

A typical example is high P nutrients. P is an anion (negative charged) so to take it up the plant releases a positive hydrogen ions (H+). The concentration of H+ is what the pH level determines, the more H+, the lower the pH.

The nutrient elements, the ions (cations and anions) move throughout the pot, partly by a process called diffusion, partly by water uptake/movement. This results in different concentrations of nutrients throughout a soil container. That in turn (because certain ph values are better for take up of certain elements, which influence pH) leads to different pH values throughout the pot. Which in turn, as I mentioned earlier, is actually an advantage, there's always a spot in the pot where the plant can take up zinc, and a spot where it can take up N easily etc.etc.

By trying to steer the pH you take over the job from the plant and that doesn't always lead to a better situation (often not...). Also once you start controlling you generally have to continue doing so.

The pH value, in soil too, is important because certain elements are easier to take up within a certain pH range. It differs per element, there's not 1 specific optimal pH value, it's a range that includes all elements. A common mistake hydrogrowers make is keeping the ph strict on 5.8 while it's good when it fluctuates a little between low (good for micro uptake) and high (good for macro uptake).

i'm sorry for the confusing post--i meant that measuring for PH in soil is not necessary, not that the PH doesn't matter. thank you very much for the additional information.

sunny747 said:
That could explain why I still get lockout even when PH'ing. I don't own a TDS, but I know my tap water is SUPER hard, high TDS.. My Hydro guy was telling me that the water just gets too congested for the nutes and cal/mag to work correctly.. Kind of like a traffic jam..

someone stated earlier in the thread something about not having to worry about the PPM if one isn't overfeeding--i've noticed a major improvement in how often i feed. water here is hard too and it helped backing off of the camg+

Sativied · Feb 17, 2015

This resource is a little tricky cause if I remember correctly the soil on Maui is special, but I rarely bookmark anything but did with this one so should be good

http://www.ctahr.hawaii.edu/mauisoil/manage.aspx

If you grab 5 of such charts you get 5 different ones (especially when including hydro), don't put too much value in the values in this specific chart, but, they usually do all point out the same thing. Too high locks out micros, too low locks out macros. Low end is usually worse than high end especially for longer periods. A very common problem with hydro growers is lowering the pH too far, it's partly why Calmag can exist, not because there's not enough (any complete nutrient line contains plenty of both, and especially plenty of Ca if you also use high ph/ppm tap water with nitric acid) but because it's locked out.

I normally grow on hydro, just finished an organic water only run, going to do a Cana Terra Vega+Flores run next. They recommend 5.8-6.2 on the bottle. I won't be doing that. Well, 6.2 maybe, but definitely not 5.8. Besides that it's not necessary, it takes one or two days of miss-fertilizing to end up with 5.2 or so and premature yellowing (which people then try to "fix" with calmag).

undercovergrow said:
water here is hard too

Which means it has a high amount of Ca in a form the plant cannot directly take up. Adding nitric acid as ph down results in a chemical process that converts the Ca to a useable form. (Credit to @churchhaze ). If you have high ppm and high pH water and high Ca (usually go together) that alone can be a good reason to use ph down (nitric acid specifically, not phosphor aka pk down "bloom/flower") on your tap water. The problems usually start when someone tries to lower the pH of the soil by lowering the tap water too far, and not by lowering the tap water that would otherwise increase pH level too far.

undercovergrow · Feb 17, 2015

Sativied said:
This resource is a little tricky cause if I remember correctly the soil on Maui is special, but I rarely bookmark anything but did with this one so should be good

http://www.ctahr.hawaii.edu/mauisoil/manage.aspx

View attachment 3353532

If you grab 5 of such charts you get 5 different ones (especially when including hydro), don't put too much value in the values in this specific chart, but, they usually do all point out the same thing. Too high locks out micros, too low locks out macros. Low end is usually worse than high end especially for longer periods. A very common problem with hydro growers is lowering the pH too far, it's partly why Calmag can exist, not because there's not enough (any complete nutrient line contains plenty of both, and especially plenty of Ca if you also use high ph/ppm tap water with nitric acid) but because it's locked out.

I normally grow on hydro, just finished an organic water only run, going to do a Cana Terra Vega+Flores run next. They recommend 5.8-6.2 on the bottle. I won't be doing that. Well, 6.2 maybe, but definitely not 5.8. Besides that it's not necessary, it takes one or two days of miss-fertilizing to end up with 5.2 or so and premature yellowing (which people then try to "fix" with calmag).

Which means it has a high amount of Ca in a form the plant cannot directly take up. Adding nitric acid as ph down results in a chemical process that converts the Ca to a useable form. (Credit to @churchhaze ). If you have high ppm and high pH water and high Ca (usually go together) that alone can be a good reason to use ph down (nitric acid specifically, not phosphor aka pk down "bloom/flower") on your tap water. The problems usually start when someone tries to lower the pH of the soil by lowering the tap water too far, and not by lowering the tap water that would otherwise increase pH level too far.

thank you. i'll try lowering the pH of the water for the one plant that is having a hard time and see how things go from there.

a senile fungus · Feb 17, 2015

@Sativied

I really wanna smoke a joint with you.

Hit me up if you're ever in the states, I'll pick you up from the airport.

I thoroughly enjoy reading your posts and I nearly always learn something from you.

Thanks again.

Is ph up and down needed for soil grows?

a senile fungus

Well-Known Member

Sativied

Well-Known Member

undercovergrow

Well-Known Member

Sativied

Well-Known Member

undercovergrow

Well-Known Member

a senile fungus

Well-Known Member