pH

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gonewild

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I bought a small inexpensive pH meter and did some tests today and the results surprised me. Comments and discussion welcome.

Source water....
Tap water: pH 7.5
R.O. water: pH 6.8

(Result water samples are from s/h reservoirs in 3 inch pots)

Fertilizer solution.....
MSU fertilizer at 100 ppm N: pH 4.4
results=
Small Phrags in leca(PA): pH 5.7
Large Phrags in leca(PA): pH 4.3
Paphs in leca(PA): pH 5.3
Paphs in Sphag: pH 4.3

Fertilizer solution.....
MSU fertilizer at 50 ppm N: pH 5.6
results=
Small Phrags in leca(PA) top dressed with oyster shell: pH 6.5
 

suss16

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What is the PH of the water that you ferilize with?
 

gonewild

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suss16 said:
What is the PH of the water that you ferilize with?
Two different concentrations. Both have a little added Epsom salt with the MSU.

Fertilizer solution.....
MSU fertilizer at 100 ppm N: pH 4.4

Fertilizer solution.....
MSU fertilizer at 50 ppm N: pH 5.6
 

gonewild

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The mixture of new and old primeagra tests about the same as the straight old PA. If anything it might be slightly lower. I'll soak a couple cups of each overnight in RO water and see what the difference is.
 

suss16

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I typically correct the PH (to 6.5) of my fert prior to applying. I use pro tekt with MSU or Dyna Gro 795 & Cal/Mg to adjust the PH up. I use R/O water and have similar readings (Tap = 7.2 and 70 ppm TDS after R/0 = 7.0 and 15 ppm. Since I have great tap water I use it to flush and then apply the fert made with R/O after. I have not top dressed with oyster shell yet... But do test the ph of the "flow through" on occasion to see how my media is effecting the PH.
 

gonewild

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suss16 said:
I typically correct the PH (to 6.5) of my fert prior to applying. I use pro tekt with MSU or Dyna Gro 795 & Cal/Mg to adjust the PH up. I use R/O water and have similar readings (Tap = 7.2 and 70 ppm TDS after R/0 = 7.0 and 15 ppm. Since I have great tap water I use it to flush and then apply the fert made with R/O after. I have not top dressed with oyster shell yet... But do test the ph of the "flow through" on occasion to see how my media is effecting the PH.
What does your flow through test at?
What I would like to see is what your reading is for the small amount of water that will drain out of the pot when you tip it.
 

suss16

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I figured you would ask... I have a couple of plants in S/H so I tested one. both the PH and TDS was similar to what I fertilized with. I use Hydroton as a media, so I am not surprised they are close - I believe it has a neutral affect to the Ph? When I do a pour throug test (most of my plants are in a chc/hydroton/charcol mix) I follow the instructions in the article by Bill Argo Phd. Between that article and the ones written by Yin-Tung Wang, Bob at Antec's there is still a whole for me to figure out and apply to my growing conditions.
 

gonewild

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suss16 said:
I figured you would ask... I have a couple of plants in S/H so I tested one. both the PH and TDS was similar to what I fertilized with. I use Hydroton as a media, so I am not surprised they are close - I believe it has a neutral affect to the Ph? When I do a pour throug test (most of my plants are in a chc/hydroton/charcol mix) I follow the instructions in the article by Bill Argo Phd. Between that article and the ones written by Yin-Tung Wang, Bob at Antec's there is still a whole for me to figure out and apply to my growing conditions.
What are the results of the pour through test from your chc/hydroton/charcol mix? Or is that the result you stated above?
 
E

Eric Muehlbauer

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I always adjust my fertilizer solution with Pro-Tekt when I fertilize paphs. I use 1/4 tsp Pro-Tekt to 1 tsp MSU pure water formula....at that concentration for strap-leafed paphs, half the concentration for other paphs. I use MSU without Pro-tekt for phrags and other orchids. I used to use a pH monitor, but I don't bother anymore. I aim for a pH slightly below 7 for paphs. I have not tested runoff water, but I use CHC, which should not acidify the media. I don't use sphagnum on paphs, except for delanatii (which also gets bark, and sometimes the same fertilizer solution as the phrags, without Pro-tekt). Take care, Eric
 

Candace

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Can anyone recommend a decent, cheap ph meter? I've never checked or monitored my ph. Ever. Should probably see where I'm at.
 

gonewild

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Eric, I think it is important to also know the run off pH. That is what the roots are actually growing in. But your right it is not something that needs to be monitored once you get your growing methods how you like them.

The test I did showed that larger faster growing plants have a much lower pH than smaller ones. This indicates that the plants are drastically lowering the pH based on their consumption of nutrients. I think?

I'm not seeing any growth problems and I am very pleased with my plant growth. However a pH of 4.3 on the plants seems dangerously low, does it not? Now I wonder if they would be doing even better if I add the pro-tekt.
 

suss16

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The results I provided before are ones I just took from a S/H. When I did my other pour throug tests in my chc/hyd/char mix it was newly repotted plants and there was little change. I wanted to create a baseline to compare to tests taken 6 months later - I will tell you in 4 months what the result is.

Eric - what is the Ph of your fert with no pro-tekt that you feed your phrags?
 

Ray

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Candace,

I asked several local and an online (orchid growing) water specialists a couple of years back, the the consensus was that the "Oakton pH Tester2" was the best "field" unit. It was about $100, and I got a box of single-use pH standards to calibrate it.

A comment about the "runoff" testing: It's not necessarily that good of an indicator of what the root zone sees. It may very well be a good indicator of the immediate influence the medium has on the pH, but there's a lot more going on than simply instantaneous solution-medium interaction. To name a few:
  • Slower, time-related interaction between the medium and the nutrient solution. For example, pouring water through pure bark doesn't extract as much tannin as is ultimately released when it is kept moist.
  • The influence of photosynthesis and plant respiration through the roots. Those emitted gases are going to be absorbed by the moisture in the medium. We have seen some pretty surprising changes in S/H reservoirs.
  • The absorption of nutrient ions at different rates by different plants. The "ideal" nutrient solution would have the ions present in the concentrations needed to maintain the same fractions, relative to each other, that the plant is absorbing. I speculate that individual plants have individual nutritional needs, hence formulas, so how can you do that?
 

Rick

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I also shift the pH of my fertilizer water up to 6-6.5 for non calcereous species, and around 7.2 for the calcerous lovers. I also use oyster shell in the mix for calcerous species and for more acid loving plants I may use combinations of sphagnum and bark instead of CHC.

The buffering capacity of RO water is 0 so its real easy to have the pH influenced by the substrate without additional buffers. So thats were the oyster shell in the potting mix, and a dash of mag hydroxide in the fertilizer water will help hold the soil pH up.

There was an article in Orchid magazine that showed that growth was impared (to maude type paph hybrids) at the low pH range (4-5). This may actually be a prime pH for some oddballs like Cyp acule, and Phrag vitatum. I suspect that there are some acid loving paphs in the barbata group that will do good at low pH too, but I think the majority of slippers will apreciate soil pH in the 6-7 range over the long term.

This disertation may start to cause some confusion since I am not defining values for soil pH, irrigation/fert water pH, and run off water pH very well.
 

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