pH

[Rick]

Barring what happens in semi hydro systems (I have no experience). If you send buffered water into the pot at about pH 7.5 and it comes out of the bottom at 4-5 then I'd say your mix is breaking down, and should be changed (for most of our plants).

If you are working with poorly buffered waters (RO and even RO/MSU with pH raised with KOH) it won't take much acid in the mix to drop the pH as it passes through the pot, and should not neccesarily be a signal to repot. But if your mix has a calcerous buffer added and the pH of the irrigation water is around neutral, then you should expect the run off water to be close to neutral.

I did monitor these conditions for my rothchilidianums to maintain pH in the root region in the 7-8 range. Wild roths are found over serpentine which has been known to have a pH as high as 11 (but probably less than 8 around plants with humus deposition. The magox realy helped for this.

 

[Rick]

There's lots of sources of pH meters. You might look up Cole Palmer as a distributor. I think they carry Oakton equipment too.

 

[Eric Muehlbauer]

As I recall, the pH of MSU without Pro-Tekt was closer to 6...MSU is the least acidic fertilizer I have used, I assume because it has the least P....usually, the P is from phosphoric acid. I read somewhere, I think on this list, and it was attributed to the Wellensteins (but it was not a post from Bob...), that phrags get less browning of leaf tips when the fertilizer is more acidic. (Bob, is this your experience?) Take care, Eric

 

[Ray]

I didn't think the phosphorus in most fertilizers is H2PO3...don't they tend to be phosphate minerals?

 

[Rick]

I didn't think the phosphorus in most fertilizers is H2PO3...don't they tend to be phosphate minerals?

In my MSU from Robert's its form is monopotasium phosphate.

The buffering capacity of RO water is 0. You can just about sneeze on it and drop the pH from CO2 turning into carbonic acid.

The phosphates, nitrates, and iron can easily push the pH down to below 5 in RO water (which is what I normally see), but it raises quickly with KOH adjustment. You might also get the mixture pH to raise just by aeration, but I haven't tried that one yet.

I often add ST at a 1/4 TSP/gal. That definitely forces the pH into the 3-4 range, and it will require about 2X the amount of KOH to raise the pH back to around 6.5

 

[Bob Wellenstein]

I would strongly suggest that people investigate using potassium bicarbonate for buffering acid. I used pro-teckt for years with some reservations, but it worked, while trying to track down a (non USP - costly at our volume) source of potassium bicarbonate. I knew it was used in the baking industry and available. Then, two years ago Griffen Greenhouse supply started carrying it in 25 pound buckets. Maybe this is another product for Ray to repackage into quantities useful for hobby growers. Plants like bicarbonate, they've told me so! Griffen is on the web, so 15 of you write Ray and ask him for a 1 lb package so he can justify getting a pail.

Eric, I did a lot of playing around with several hundred Phrags on water tables in inert medium. Varying fertilizer concentrations first and then varying pH. I ended up concluding that under those circumstances, inert medium never drying out, that the fertilizer concentrations did not seem to correlate with leaf tip browning, but pH around 5.5 to 5.8 minimized it while it became worse as the pH approached neutral. (All you folks with Kovachii seedlings please be aware that this is a very different Phrag, growing in quite alkaline soil so this will not apply to it) Higher ambient temperature and lower humidity were other conditions that exacerbated the problem. Having no serious interest in Phrags outside of some of the species I took this no further, someone should repeat it but you need some serious space as you'll want a couple hundred plants.