How To Tell The pH Of My Fert?

[ShadyStump]

I splurged on a gardenia last payday (I'm broke, but totally worth it ) and everything I've been reading on them says to only use an acid based high nitrogen fertilizer.

Now I know my high school science and about pH and all that, but I don't know how to tell from reading the bag if my fertilizer is more acidic, basic or neutral. I know most are salt based, and it's often on the label, "for acid loving plants," but I know that's not always the case.

What can I look for on the, "ingredients," list that will tell me?
Potash is a salt I know, but what about amonium compounds, etc?

 

[Tums]

I believe the type of nitrogen helps determine how acidifying the fertilizer is. Ammonium has the most effect followed by urea, and nitrate source nitrogen has the least. Here's an extension article on it https://hort.extension.wisc.edu/articles/reducing-soil-ph/

 

[Wires_Guy_wires]

Best way to determine it is to get a bunch of cheap lackmuss or litmuss strips from a aquarium store or a pool shop or something. They're about 50 cents for a 100 strips. The quality is almost always the same, so cheap or expensive doesn't matter much. You need a millimeter of testing strip, so you can cut them to size, giving you a couple hundred of them, maybe a thousand.
Grab a cup of water, test it, add fertilizer, mix, test again with a new strip. If it lowers, it's acidifying. If it rises, it's alkaline.

Sulfur usually isn't mentioned on the label, as are many compounds, especially in organic fertilizer.
Things get difficult when there are water-bound salts and buffering molecules like ammonia, or EDTA-bound metals in chemical fertilizers. So if you're not up for filling in an entire excel sheet and running calculations with 5 or more vague parameters (not everything is required to be on the label) it's easier and faster to just use a test strip.

Sulfuric acid drain cleaner is pretty cheap and if there aren't any soaps added to it, it's a great way to lower the water pH in a single drop.

 

[penumbra]

Sulfuric acid drain cleaner is pretty cheap and if there aren't any soaps added to it, it's a great way to lower the water pH in a single drop.

I have recently been using citric acid powder (small dissolving granules actually). I am still experimenting but 1/4 teaspoon in a 5 gallon bucket lowered my pH from 7.8 to about 6.
I figure I take vitamin C so why shouldn't my tropical plants. I am planning to use it with a Hose On, siphon feeder for my satsuki azaleas this year.

 

[Glaucus]

Only aqueous solutions have a pH. So unless your fertilizer is liquid, it does not have a pH.
That said, Ammonium and urea are basic, because they strip water molecules from their H+ ions, creating a OH- and changing the autoionization balance of water, increasing H+ concentrations.

BTW, vitamin C is ascorbic acid, not citric acid. But no worries, you probably consume more citric acid than ascorbic acid. Even though the 'if it is good for me, it is good enough for my plants' is a really bad standard. Us humans don't like to choke on CO2.

Usually, organic fertilizer is acidic, because the way organic molecules break down often results in acids.

 

[Wires_Guy_wires]

I have recently been using citric acid powder (small dissolving granules actually). I am still experimenting but 1/4 teaspoon in a 5 gallon bucket lowered my pH from 7.8 to about 6.
I figure I take vitamin C so why shouldn't my tropical plants. I am planning to use it with a Hose On, siphon feeder for my satsuki azaleas this year.

Citric acid and ascorbic acid are two different things ;-) but they're usually mixed in vitamin C tablets to give them a citrus taste.

Citric acid is a weak acid, like acetic acid. This means that it can serve a buffering function: release a H+ or take up a H+.
Make sure you measure again after a while or keep stirring, because the pH can rise again - due to that buffering - once the molecules are homogenously mixed.
You might measure 6.00 but 20 minutes later 6.80. Not that big of a deal, but it could make a difference.

 

[ShadyStump]

This is what I have on hand, purely for the sake of example. Osmocote knock off.

I like this brand because, if nothing else, they provide lots of detailed information about all their products right on the package.
Seems to be fairly well balanced nutrient wise, and from what I'm gathering from your responses formulated for an end result of pH neutral or close to.

What could I do to take this or something similar down a notch? Add a bit of white vinegar as a mildly acidic buffering agent like @Wires_Guy_wires explained?
Or does the actual chemical make up of the nutrients make the difference? Like, must it be acidic compounds delivering the N, P, and K, not just whatever but in an acidic environment?

 

[Tums]

Lowering the ph of irrigation water has worked for me. Over time your soil media ph will drift towards your irrigation water ph barring any strong buffers in the soil.

 

[Wires_Guy_wires]

This is what I have on hand, purely for the sake of example. Osmocote knock off.
View attachment 421958View attachment 421959
I like this brand because, if nothing else, they provide lots of detailed information about all their products right on the package.
Seems to be fairly well balanced nutrient wise, and from what I'm gathering from your responses formulated for an end result of pH neutral or close to.

What could I do to take this or something similar down a notch? Add a bit of white vinegar as a mildly acidic buffering agent like @Wires_Guy_wires explained?
Or does the actual chemical make up of the nutrients make the difference? Like, must it be acidic compounds delivering the N, P, and K, not just whatever but in an acidic environment?

I too would lower the water pH to your required level. These slow release things release their things slow, so even if they lower the pH, the effect is dependent on a couple factors you kind of want to exclude because they are difficult to control.
Rainwater over here has a pH of around 5.5-6.5 so I give some plants only rainwater.

In soluble nutrients, the compounds matter more. But most soluble or liquid nutrient mixtures lower the pH by themselves a good two or three points.

 

[ShadyStump]

That still leaves me wondering what the difference might be between basic nutrient compounds added to an acidic environment, vs acidic compound nutrients to begin with.

Example, is adding potassium salts to an acidic soil the same as finding and acidic potassium source?

Edit: I'm looking for very general understanding more than just advice specifically for my gardenias.