pH paper might be accurate enough for many gardeners if it is used correctly!

Among pH paper options pHhydrion pH test strips perhaps work best. That is if an appropriately representative soil sample is both taken and prepared correctly. You also need to just drip it and remove and not let it sit too long before reading because the dyes can extract and wash or drip off.

Test strips of any kind must be stored correctly so thst they are not sun bleached or contaminated. I forget if they have an expiration date or not to help avoid risk from being effected by airborne acids or bases over time? For instance trace levels of vinegar (acetic acid) or ammonia. In any case store in their container or buy new ones if they are very old or stored with too much humidity.

I have a fish pond and hense always keep pHhydrion strips on hand.

If more accurate or reliable methods are desired, or you neef to verify that an alternate method is working it's hard to beat a pH meter. Local garden clubs likely have member or two with a pH meter. You can perhaps just take your sample and/or test method that you want to test there and.get help.

Quick and dirty calibration standards if you can accept the risk.

Lemon juice - 2.3

Tomato juice - 4.2

Milk - 6.3-6.6

Egg whites - 7.6-8.0

Ammonia cleaner: pH=11

If you can muster up enough, a typical persons saliva has a pH of 6.3-6.6.

More morbid or at least taxing on someone, human blood has a pH of 7.35-7.45.

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Home lab calibration buffer recipes also exist. Some quick survey examples follow below (I've not verifed them in a lab). To make these you need to be able to first weigh things accurately. A Digital Gram scale would likely be accuate enough. Examples can be under $35.

Amazon.com: lab scale https://www.amazon.com/gp/aw/s/ref=is_s?k=lab+scale

Home Calibration Solutions if you don't mind taking a risk

For Base Range (pH > 7)

-Sodium bicarbonate (baking soda) - 8.5g dissolved in 1L of distilled water: pH=8.3-8.4

Sodium borate (Borax)- ~1 wt% solution in distilled water: pH=9.2

For Acid Range (pH < 7)

-Potassium Bitartrate (cream of tartar) - 19g dissolved in 1L of distilled water: pH=3.6
5wt% acetic acid (distilled vinegar): pH=2.4-2.5

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Better solutions can be made by mixing two or three known chemical components by weight and dissolve them in a known amount of water. Then you have to be able to accurately measure liquid volumes.

This link gives more professional lab type methods requiring accurate solid weight and liquid volume measurements.

Preparation of pH buffer solutions http://delloyd.50megs.com/moreinfo/buffers2.html

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Remember however that your pH measurements are only as accurate as your calibration standards. This is why labs buy them from trusted sources!

Note that Amazon lists sets of 2 or 3 professional liquid calibration buffers for around $10-15.

Amazon.com: ph calibration solution https://www.amazon.com/gp/aw/s/ref=is_s_ss_i_014?k=ph+calibration+solution&sprefix=ph+calibration

Here's some examples of powdered calibration buffers in capsules to make smaller lots of liquid calibration buffers. These are nice because they store well if you don't need them awhile.

Amazon.com: ph calibration buffer capsules https://www.amazon.com/gp/aw/s/ref=is_s?k=ph+calibration+buffer+capsules

Examples of economical, perhaps "good enough" for gardening, pH meters

This Vantacool portable pen pH meter is available for $25 to $50 sn can be calibrated with three buffer set points including pH 4, 7 and 9. The only negative feedback I see for it seem from people that feel pH paper is sufficient (i.e., wanting the low cost wins option) and there was a unit that didn't work electronically.

Vantacool Digital PH Meter, PH Tester with ATC,Water Quality Tester 0.01pH High Accuracy, 0.00-14.00 Measurement Range, 0.01 Resolution Measure Household Drinking Water (YELLOW) https://www.amazon.com/gp/aw/d/B01G5BLJ20/ref=psdcmw_13764331_t3_B00HAKAFGC (Share from CM Browser)

In contrast, many of the $15 meters that physically look like this are calibrated to one buffer only. With these you need to use a buffer near the pH of the samples that you are meauring! The further away you measure, the more it may be off. I'd try to calibrate it will a butter within 1, max 2 pHs away. For interest to measure samples in the pH 6.5 range it is best to use a 6.5, 6 or 7 buffer. Next best is 5.5 7.5. If you use pH 4.5 or 8.5 buffer, good luck. You might be ok but I'd worry about being off 0.5+ pH units in your measurements.

Knowing the soils pH is one part of the equation. You also need to know the ratio of Calcium to Magnesium.

Most all nutrients are most readily available with a soil pH in the 6.0 to 7.0 range, but then there is a wide range of plants that have evolved growing in soils with much different soil pH.

kimmq is kimmsr

Yeah ... lots of critical things to consider

such as initial and changing pH effects*, buffering, multivalent cations, anionic and cationic micronutrients, and zeolite like ion exchange surfaces on soil particles, which make it a play day for chemistry discussions.

Then the attack and breakdown of plant and animal litter to slow release nutrients brings up neat microbiology and biochemistry aspects.

Material science then decides to manipulate the situation with osmotic release and diffusion of encapsulated nutrients. And hydroponic principles try to partially play nature taking over the hydrology and lighting it up.

Physics kicks ideas in there on this last aspect. For instance did you know that fluorescent light indeed glow when struck by energy (as you know), but much of the light intensity flashes through a series of distinct colors at 60 times a second?

* Plants cheat neatly by manipulating ion exchange release of cationic nutrients. They knock off ammonium, potassium, magnesium, calcium and other positively charged ions by producing acid(s) to knock it off. H+ alone can cause the exchange but if the acid is on a small organic base (anion) like oxalate this organic can diffuse around and pull at the cations on soil that the plant wants and help knock it off, helping in the "weathering" breakdown of soil too.

Chelators made by plants and microbes make it really interesting too. They diffuse around and hold certain critical nutrients so tightly that the plant has the choice of finding more, having a deficiency (specific nutrient starving), making a stronger chelator to take it back, and/or breaking the chelator down to free the nutrient.

Now the fun parts ... the plant one might be considering is not be alone. A group of similar or different roots might be working together AND competing in that patch of soil, with different players at different depths Trees cheat and certain non woody plants cheat and go low.

Moles, gophers and field mice run through this soil zone toox playing their games. No soil contact then no nutrient uptake, no root then no nutrient collection there for the plant, loss of stored nutrients and need to spend energy replacing the root.

And there are smaller life forms co-inhabating the soil with the roots that are also directly or indirectly effected by soil pH. Let's put them into three classes as those that (1) don't generally effect a plant much, (2) can hurt the plant, or (3) can help the plant. Let's see ... hurting a plant is bad, unless it hurts a seriously competitive plant more. Helping a plant is good, unless it's again that serious competitor.

Plants are not stand alone organisms in naturem. They live in community with microorganisms. So what if the soil pH helps support the growth of a microbe that can grow all over your plants roots?

Sounds bad I know, but there are those three classes mentioned above. If your microbe is a pathogen that is bad. If it doesn't attack the plant but runs out and breaks down nearby leaf litter, great free food. It it doesn't hurt your plant but by being on root surfaces can compete with and stop pathogenic microbes from getting a foothold, great a free natural inoculation for immunity.

There was a company called Eden Bioscience a couple decades ago here in the PNW that made an interesting observation. In large scale evergreen seedling production for forestry sometimes there were large scale fungal blights. Sadly alot of the seedlings all died at once in mass. However, sometimes there were a few seedlings near each other that did not succumb! In fact they looked totally healthy!

When isolating bacteria, yeast and filamentous fungi from the surfaces of these plants they found that certain kinds could be grown in the lab that protected seedlings from attack, when sprayed onto them. These microbes grew best in their optimal pH range. They indeed colonized the plants, in this case leaf surfaces. And their presence did protect the leaves from pathogen attack. Obviously similar things must be happening in nature in the leaf canopy and also soil root zone of plants.

So when a plant likes acidic pH 5 - 6 soil, is this just because nutrients are more available it? When I went to school, in what now seems like the dark ages, most plant physiology books focused almost solely on this. Or is it because beneficial microbes helping feed or protect the plant need that pH?

My firm assumption is that both chemical and microbial pH dependent effects interact to make an optimum environment for that plant. And that some plants in the natural environment survive best, rather than grow best, at their optimal pH range.

Why do many fungi sour (strongly acidify) what they are busy rotting? Niether competive microbes nor does the dieing plant tissue like it. The fungus gets more.

This is exactly why you want to check the pH in the soil that you might be soon preparing for your new vegetable or herb garden this spring. Too basic, your plants starve. Too acidic, the pathogenic fungi don't starve. Then like the heirloom story of The Three Bears ... there's one pH that's just right.

Thanks for the recipes Gary...if only they could be converted to teaspoons per quart for the average kitchen owner, it would save having to buy a scale. Most people can't weigh out 8.5g of baking soda or calculate and weigh out borax for a 1% solution. But aside from the units, these recipes are exactly what we need.

At the moment I am actually in possession of a digital scale so I might play around with this. Granted a teaspoon won't be precisely accurate compared to weight, but if the material is a weak acid or base (as are things like baking soda and borax) the curve is pretty flat at its characteristic pH so a few percent either way shouldn't matter much.

I've been investigating what to use for a pH 7-ish buffer that is commonly available around the house. Obviously distilled water should be 7 but it has zero buffering capacity so it will drift if you look at it funny.

Baking powders might be a possibility. They are usually a mixture of sodium bicarbonate and an acidic salt like sodium aluminum sulfate or monocalcium phosphate. When water is added the acid and base react to make CO2. This would leave a buffered salt solution. Unfortunately they vary by brand but the popular brands have been around for a long time and their formulations are pretty constant. Anyone with a pH meter care to check the pH of baking powder? I'd suggest Clabber Girl or Calumet. Half a teaspoon in a pint of distilled water.

Yes there are Baking Power, Cream of Tartar, Vinegar (white 5% distilled) and Vitamin C based pH standards easily found on line. Someone could play around and come with a mixture table for getting standards a specific pH levels too.

In the lab, people making pH buffer standards often use standard mixes of acetate, phosphate, OR citrate in the sodium salt or acid forms dissolved in distilled water to make Buffers of desired pH.. Two or three of each related form is needed to make the final standard mix desired in any one of these series. Final mixture standards are generally checked against known standards to make sure they are right. However, for "gardening purposes", they are likely good enough? These methods require you to buy 2-3 simple chemicals for each series you may need. I'd want a pH 4,0 & 7,0, pH 7.0 & 9.0, OR pH 4.0, 7.0 & 9.0, depending on if I was measuring below 7, above 7, or both ranges.

Example Lab Buffer Mixing Tables http://microscopy.berkeley.edu/Resources/instruction/buffers.html

For those that feel that they only need a general standard and it can be off a bit for accuracy there are abundant ideas. Understand that one might be off as much as 0.20, 0.5 even 1.0? pH unit based on the sample used alone, and the measuring method used (if not checked separately) adds to the uncertainty.

ph of common household items - Google Search https://www.google.com/search?q=ph+of+household+items&source=lnms&prmd=ivsn&tbm=isch&sa=X&ved=0ahUKEwj6iuuxmPzRAhWLerwKHYDzC6cQ_AUIBygB&biw=360&bih=640

Many those feeling pH paper is good enough for them. Awesome, enjoy it. But note that with formerly "accurate" pH paper at times I've had poor results at times. It might have been due to with interferring chemicals or the pH paper's dye buffering capacity when measuring dilute samples.

So at least when you start measuring samples you make in your yard, it is prudent to also compare with another method to ensure accuracy. It is useful to know that a local a soil lab or standard buffer gives you the same pH result. If it doesn't, you'd sure want to know!

Note that as pointed out by others, pH is only one important soil chemical factor.

Independent labs and home indicator dye tests can also measure for specific classes of nutrients (e.g., Rapitest kits is in most gardening and home hardware stores in our area). If you use these, I'd reccomend that the test method chamber has a color guide with sample well built into it to correct for color or turbidity extracted into the test sample. The color guide comparison chamber also puts the color guide into the same viewing materials, light, and angle as the test chamber. This interests me because sample color can shift perceived test color and I've found hard at times to accurately compare a paper / air based color guide against a plastic (or glass) / water based test chamber.

There are also simple "dip strip" nutrient test kits that have bern more recently developed, which are sold online now (e.g., AquaChek in Amazon). Very tempting! If the chemistry and color comparison guide is done right it could work. Anyone have good results using these?

Finally, comparied to an electronic needle pointer or digital readout, almost any colorimetric eye judged test is less accurate. This is especially true unless the color guide has distinct color changes over a narrow value range or if it has a multiple color [e.g., tri-spot) series to compare for each value.

One might not be able to see better than plus or minus 0.2 to 0.35 pH units with many pH strips I've used. And good luck if you are even partially color blind in that color range (this most commonly happens in the blue/green range). Consider looking into the color guides for the kits that you are thinking of purchasing. If you can't sufficiently distinguish between adjacent pairs of colors in the color guide, then don't get the kit unless you can either accept that uncertainty range, or you have a friend that can see those differences well.

I did quite a bit of searching this morning on the pH of household products after reading your previous post. I like baking soda for >7, tartaric acid for <7, just looking for a good neutral standard. Milk (6.3-6.6) is a good idea, you would think it's pretty buffered from all the 'stuff' dissolved in there.

Of course, when you calibrate most meters, you do one solution and then the other (as described earlier). If you are measuring an alkaline pH, it's good to calibrate at neutral + high end; for low pH samples, neutral + low end. Or, low and and high end, and use the neutral one just as a check. Whatever you do, it's a good idea to do it the same way every time. That way, even if your system is off by a couple tenths of a unit, at least you are comparing apples to apples from one test to the next.

No one seems to list the pH of baking powder solutions, probably because the formulations vary by brand. I will see if one of my lab friends can check it out.

Yes, one would expect fresh milk to have a pretty stable pH. If spoiling however it will drop rapidly. Agree baking powder risky. Baking soda however is more uniform.

List for pH values at room temperature*

2.0 Lemon Juice

2.2 Vinegar

3.0 Apples

3.0 Vitamin C. Pure, at 5%

3.6 Cream of Tartar saturated solution

4.0 Wine and Beer

4.5 Monosodium Phosphate at 1%

4.5 Tomatoes

6.6 Milk

8.4 Baking Soda (bicarbonate), 1g 400 mL

9.1 Disodium Phosphate at 1%

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*Room temperature considered 77°F = 25°C.

Funny there is a big hole right around 7. You'd think there would be more choices there.

To get pH 7, one generally needs to mix more than one component. And things need to be done right. The solid chemicals must be stored desiccated and one must weigh solids and measure liquids quite accurately.

Typical quart, pint, cup, tablespoon and teaspoon measuring devises and pound or ounce weight measurements are not accurate enough. Use beaker, graduated cylinder, and pipettes for liquid measurements and weight scales calibrated in grams.

Thus, reconsider just buying standard pH buffers from Amazon or other lab supply sources. Besides being easier to just purchase the standards have also been verified to be accurate and are correctly preserved to store well refrigerated.

For those who still want to make their own.

pH 7 buffer is often made with Phosphate salts. They actually work well anywhere within the pH 5.8 to 8 range. Below is a link to a great little calculator to show you what to mix. The documentation there also how such calcuations can be made with Phosphate or any other acids and bases.

Phosphate Buffer Calculation (using Javascript) http://clymer.altervista.org/buffers/phos2.html

Depending on your scale's weight measuring range, I'd recommend making 100 or 1,000 (1 liter) of 200 milli-molar buffer. The calculator link above will show you need 1.06g Monosodium Phosphate and 3.30g Disodium Phosphate dissolved into 100 ml final volume.

pH 4 or 9 buffers are often made with Phthalate or Tetraborate (Borate) salts, respectively. The link below gives examples of these and for pH 7 phosphate..

Example with pH 7 phosphate buffer.

Add 6.81g potassium dihydrogen phosphate to 291ml of 0.10M NaOH solution, then adjust total volume to 1 Liter. Make 0.1 M NaOH solution by putting 4.0 g NaOH soild into 1 Liter water..

Source: http://www.google.com/url?sa=t&source=web&cd=4&ved=0ahUKEwiY-K7__YDSAhUJKGMKHVJ1BU8QFggkMAM&url=http%3A%2F%2Fdelloyd.50megs.com%2Fmoreinfo%2Fbuffers2.html&usg=AFQjCNH3lLDXWRtKbtLjlV6ZBtYO9uNIqA&sig2=d4vX6ZJ943ARCevuAXsL7Q

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For those wanting more information

How to Make a Phosphate Buffer https://www.thebalance.com/how-to-make-a-phosphate-buffer-in-8-steps-375497

Reagents Buffers and Indicators

http://www.google.com/url?sa=t&source=web&cd=2&ved=0ahUKEwiK_vq9-4DSAhVH2mMKHSdiDtgQFggdMAE&url=http%3A%2F%2Fpubs.acs.org%2Freagents%2Fdemo%2Fpart3%2F02-ReagentsBuffersIndicators.pdf%3Fsessid%3D6450&usg=AFQjCNGGwFjz2rfkI9fT9AU5rBHxan0XWg&sig2=vAWhTaWIvbR19EJJqyL2LA

Table of 600 Acids and Bases

http://www.google.com/url?sa=t&source=web&cd=2&ved=0ahUKEwjAkKOe-YDSAhVS4WMKHQKfAj8QFggcMAE&url=https%3A%2F%2Flabs.chem.ucsb.edu%2Fzhang%2Fliming%2Fpdf%2FpKas_of_Organic_Acids_and_Bases.pdf&usg=AFQjCNG8SpTbrj3FTIF7UgD8_5yMRNsftg&sig2=HCr0NafT77l7mYIJcVxIJQ

Hey I found a great resource for pH calibration: commercial soft drinks.

https://www.ada.org/en/~/media/ADA/Public%20Programs/Files/JADA_The%20pH%20of%20beverages%20in%20the%20United%20States

Here's a study from 2016 of hundreds of commercial drinks. I bet they are carefully controlled at the factory so you can depend on these numbers. Most of the colas and such are very low - 3 or even less! - but A&W Root Beer for example is 4.27 which is just below even peat moss so it's perfect for the acid side of the scale. Or select anything you can get your hands on.

Milk as we said earlier in this thread is about 6.3-6.6. I like that for a neutral one (if you're not into buying and weighing the phosphate salts mentioned above). Baking soda or borax are good for the alkaline end.

Just thought I'd post the soft drink thing because I hadn't thought about it before.