pH and Nutrient availability chart

[VerdantGreen]

Hi all, i thought this chart might be useful and it ably illustrates why the Burn1's recommended addition of powdered dolomite lime is a good idea, because around pH7 is a good basis for having most nutrients available to your plants. Its also a good insurance policy against pH problems messing up your grow.

probably not essential I actually go one step further and reduce the pH of my waterings to around 6 or just below. Then you get a sweep of pH between 6 down to 7 (as the dolomite in your soil buffers pH back up to 7) over a few hours and you get optimum availibility for nearly all of the nutrients that the plant requires

hope this helps someone
stay safe
V.

p.s. if a mod can make it so the chart appears full size in this post them please make it so

managed to work it out!

 

[Blue Dot]

I agree, this is the best chart to use because the other charts out there are not truly representative, but IF you draw a line straight down from pH 7.0 you will see that your metal micro-nutes will not only be at bare minimum limit but that iron will be limited.

BTW, notice the ammonium. A lot of people never look at that and continue on feeding with their crap miracle-grow.

This is why miracle grow, with a higher % of ammonium to N, is bad whereas FloraNova with like 90% Nitrate N is the way to go when dialing in at a pH of 5.9-6.5.

If you use 1 TBS dolomite lime/gal soil your pH WILL always come in at 7.0 on the nose (this is bad).

If you use 1 tsp/gal dolomite lime you will hit 6.0-6.5 pH (this is good).

PS, just remove the thumbnail html in your pic and it will show full size.

 

[VerdantGreen]

hey blue dot - im sure that works for you but what happens if the dolomite runs out and stops buffering before the end of your grow??

thats why i prefer to use the prescribed amount of dolomite and then adjust the pH to get that sweep between 6ish and 7. you will find also that most liquid nutes will lower pH of your water anyway - and this helps them work. (always adjust pH AFTER you have added your liquid nutes)

i would be interested what others think about this.

 

[Blue Dot]

powdered dolo lasts 2 years to peak (pH 7.0) then fades for another 2 years back to baseline (where you started before you added the dolo).

I'm way too tired to search for the graph depicting this right now (google it).

 

[VerdantGreen]

that sounds right mate, but doesnt a buffer has to be available in sufficient quantities in order to do it's job? and doing its job of buffering will use it up, being a buffer using more than you need will not (within reason) do any harm, but using not enough may mean that it is not buffering towards the end of your grow.

i mean if there was another organically acceptable buffer that buffered to pH 6.5 or so then that may be preferable to dolomite, but i have never heard of one so i would prefer my pH to be buffered to 7 where it is close to ideal reather than leave it to chance.

and watering at 6 will, imo, give the best of all possible worlds.

V.

 

[Clackamas Coot]

Organics & PH

 

[VerdantGreen]

i did an experiment with powdered dolomite lime the other day and thought the results were relevent here because they showed that, once the dolomite has bought the pH down to around 6, the buffering effect slows down and you get a lovely sweep between 6 and 7 that lasts a 8hrs or so, which gives plenty of time for nutrients to be absorbed at their optimum pH.

I took a glass of water and put a tiny shot of my citric acid solution into it .
I measured the pH with my pen and it read 5.1.

(YES, I am an organic grower with a pH pen, part of a rebel alliance of heads that like to know the acidity of their water, the pHorce is strong within us – deal with it! )

I then took a half teaspoon of powdered dolomite lime and stirred it into the acidic water. Here is what happened to the pH :-
Original pH before addition of Dolomite = 5.1
1minute - pH had risen to 5.3
5 minutes – pH had risen to 5.8 – so within minutes we have a much more desirable pH plant-wise!
15 minutes – pH was 6.0 – doing its job nicely.
1 hr – pH was 6.3
2 hrs – pH is 6.4

ETA: 3 hrs - pH is 6.5
4hrs - pH is 6.6
5hrs - pH is 6.7
8hrs - pH is 6.9 - job pretty much done!

now I don’t claim that this experiment is mimicking the conditions in a pot perfectly, but I am very confident to conclude that powdered dolomite lime, well mixed into the soil, will do the job of buffering the pH of the soil possibly within minutes, certainly within hours of watering.

And bear in mind that the pH scale is logarithmic so a pH of 5 is many times more acidic than a pH of 6, and thus will react faster with the dolomite as can be seen in the experiment. As the pH gets nearer to 7 the buffering effect will slow down, but the pH is nearer what we desire anyway, and considering that the optimum availability pH for most macro and micro nutrients it between 6 and 7, the job that the dolomite is doing is, imo, exactly what we want from it.