pH Meter Calibration

[CodeSection]

Hopefully, I will be receiving some hop plants soon that will be planted in 10 gallon grow bags using Kellogg Raised Bedding Soil that has a pH range of 5.8-7.5. I want to measure the pH using my Milwaukee MW102 but I want to make sure if that is advisable.

I plan on taking eight tablespoons of dirt and put it in a beaker. Then I was going to add eight tablespoons of irrigation water and mix it with the soil for a couple of minutes and then let it rest for 15 minutes, then stir again and let the soil settle. Once the soil settles, I was then going take a measurement reading of the liquid only so as not to scratch or damage the probe.

Is my process correct? Will that process damage the probe?

 

[mabrungard]

I believe the method requires distilled water.

 

[day_trippr]

For best results, distilled - or at least low TDS RO water - will produce the highest fidelity results.

fwiw, I check the pH of our veggie garden three times each year to keep up with the tendency to go acidic. I scoop up tablespoon samples from five spots (corners and middle), mix them together, then pull two tablespoons of the mix, add it to two tablespoons of RO water (tds under 10) in a small screw top container, shake it up, let it sit for five minutes, then dip the meter in...

Cheers!

 

[CodeSection]

According to Wards Lab, my RO has a pH of 6.9. I guess distilled water as @mabrungard suggested would be more accurate?

 

[day_trippr]

Not at all. If the TDS is very low there's so little behind that pH reading it will be easily shifted.
Indeed, if you leave your RO water sitting out its pH it will gradually drop as it absorbs CO2. I often find my RO water reading in the low 6s.

It's the ionic content you're trying to avoid, not the intrinsic pH...

Cheers!

 

[mabrungard]

Yes, that intrinsic pH value of the RO water has little effect when its mixed with the soil matrix. The TDS of RO water should be low enough to substitute for distilled water.

 

[MadCowTX]

I don't brew beer (sounds like great fun but I can't start a new hobby). I just read this whole thread to get a better understanding of how to choose and use a pH meter for potted plants.

If it's not too late, I would very strongly recommend that you do NOT use any type of "bedding" soil, top soil, or garden soil in a pot or grow bag. You want to use a soilless medium (although it might be labled as potting "soil" and it will look like what most people think of as soil). Bedding soil, top soil, etc. have absolutely the wrong drainage and water retention characteristics for a potted (or bagged) plant of any sort. They will drown the roots with too much water and too little oxygen, taking too long to dry out between waterings. Even pre-packaged potting "soil" is virtually always far too water retentive and slow draining and, thus, does not allow enough oxygen to the roots for ideal plant growth, but it will do much better than bedding soil.

To keep things simple, I would suggest high quality potting soil such as Pro Mix or Fox Farm. If you want to go a step further, add around 20-40% perlite by volume (depending on how hot and dry your climate is). Even that "recipe" leaves much to be desired, but it will be vastly better in a grow bag than bedding soil.

To answer your question, for plants in containers (pots, bags, etc.) with soilless media, it's typically more useful to pay attention to the pH of your irrigation water/ fertigation solution than the media itself (assuming you start out with a reasonable pH, which the above suggestions will). Controlling the pH of container media can be very difficult, and unnecessary when you irrigate/ fertigate within the correct range. However, if you want to get an idea of the media pH, the best approximation you can get at home is probably with the pour-through method, not by shaking up a sample of the soil/media in water: www.css.cornell.edu/courses/260/Media%20testing.pdf

Keep in mind that most plants will want to be around a full pH unit lower when grown in containers with soil-less media vs. soil. So, hops like soil at pH 6-7 but in soilless media, they'll do better in the range of 5-6 (FYI, growing in containers is equivalent to hydroponics if you're using soilless media, which includes peat-based "potting soil", so any recommendation for pH in hydroponics would be applicable). On the other hand, if you're planning to grow organically with a living soil, ignore everything I just wrote. However, successfully growing with a living soil in a pot is a far bigger challenge than most people realize. I suggest you stick with "synthetic" fertilizers if you don't have any expertise in organic container gardening.

Finally, keep in mind that the range of pH at which plants take up each essential nutrient varies, so there's no single ideal pH. For example, a plant may take up Mn at pH 5-5.75 but the same plant may take up Ca at 6-7.5, so there's no pH at which it readily takes up both Mn and Ca. The ideal is to let your pH vary throughout the preferred range to ensure the plant will be able to uptake everything it needs.

Hopefully, I will be receiving some hop plants soon that will be planted in 10 gallon grow bags using Kellogg Raised Bedding Soil that has a pH range of 5.8-7.5. I want to measure the pH using my Milwaukee MW102 but I want to make sure if that is advisable.

I plan on taking eight tablespoons of dirt and put it in a beaker. Then I was going to add eight tablespoons of irrigation water and mix it with the soil for a couple of minutes and then let it rest for 15 minutes, then stir again and let the soil settle. Once the soil settles, I was then going take a measurement reading of the liquid only so as not to scratch or damage the probe.

Is my process correct? Will that process damage the probe?

 

[CodeSection]

I appreciate your post, thank you. I ended up using roughly 80% of this Kellogg Garden Organics 3 cu. ft. Raised Bed and Potting Mix Premium Outdoor Container Mix-649 - The Home Depot along with roughly 15% of desert dirt and 2" of my compost soil on top. Supposedly, the raised bedding mix contained sand.

I transplanted the four hop plants into 15 gallon grow bags almost two weeks ago and they have been really taking off. Even the one worse looking plant is now looking a lot better.

Since we are experience 100F+ weather here, my watering schedule has changed to about every 18-20 hours. You make a good point about my water's pH which is 6.9.

Thanks again!

 

[Mikey B]

I jus hope no one is trying to measure the pH of their tap water and think that the measurement is accurate.

 

[VikeMan]

I jus hope no one is trying to measure the pH of their tap water and think that the measurement is accurate.

Although tap water pH is basically irrelevant in regard to mash pH, I'll bite. Why?

 

[Silver_Is_Money]

Although tap water pH is basically irrelevant in regard to mash pH, I'll bite. Why?

I'm not the one who asked of it, and my answer may indeed differ, but pH meters are at their least accurate and most sluggish when measuring near or right at waters neutral pH point. And particularly more so if the water is deionized or distilled or good RO.

 

[VikeMan]

I'm not the one who asked of it, and my answer may indeed differ, but pH meters are at their least accurate and most sluggish when measuring near or right at waters neutral pH point. And particularly more so if the water is deionized or distilled or good RO.

I have noted this with distilled water. But with (my) tap water, I have not. It agrees very well with water reports. I would assume the phenomenon varies with TDS/conductivity.

 

[Silver_Is_Money]

I would assume the phenomenon varies with TDS/conductivity.

That matches my assumption. pH meters have little trouble with pH 7.01 buffers for example. I've never ran a conductivity test on such a buffer, but it is likely well up there in TDS.