Where is the "acid" in Miracid?

Today I bought some Miracid to feed my citrus. Just as an experiment, I tested the pH of the water in the watering can after adding the Miracid, and there was no change, 8.0 just as before. I then tested another sample from a watering can just using white vinegar, 2 tablespoons per watering can, and it knocked the down to 6.0. So where is the acid supposed to come from? Looks like kinda of a scam to me. I like N-P-K of the Miracid along with the macros and micros, so it looks like a little vinegar will complete the picture. Not looking to get into a debate of Miracle Gro vs other fertilizers, just wondering what makes Miracid any better for acid loving plants. Probably going to use Citrustone in the future.


Acidic soil is a condition for life for blueberries and acid loving plants. Fertilizer for acid loving plants requires a different formulation. Blueberries cant process many of the forms of nitrogen in fertilizers and need ammonium forms of nitrogen. to acidify your soil you need sulfur, bacteria and time.

Here’s what I think is going on. That fertilizer has mostly the ammonium form of nitrogen which isn’t acidic when it’s dissolved as you did. The acid is produced in the soil either when bacteria convert the ammonia to nitrate nitrogen or when the ammonia is taken up directly by the plant. So it would be net acidic in the soil after a few weeks even thou it isn’t an acid yet. It gets converted to an acid in the soil.

Elemental sulfur isn’t acidic either. The soil bacteria convert it into sulfuric acid over many months.

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Which Miracid did you buy? Scott’s makes several formulas.

Although blueberries (and Vacciniums in general) react with toxicity to Nitrates, they uptake other forms of nitrogen and minerals without incident.

A tried and true method for keeping blueberry beds acidic is to use plenty of sphagnum peat moss in the soil mix and prilled sulfur to control the pH. Follow the directions on the latter and test for a two-three month period before reapplication. It is slow acting but persistent. Once your soil is too acidic it will be a fight to raise the pH.

All is well, but the part that gets me is that the label for Miracle Gro all Purpose, and the label for Miracid is exactly the same, and I mean exactly. Bottom line for me, is that if I need to acidify my soil, I’m using another method. MG might be ok for fertilizer, but for acidification, am going another route,

Well just to let you know vinegar won’t do it either. Sure it will be acidic for a couple weeks till bacteria break down the acetic acid. It works well with containers because you can flush out the carbonates with vinegar. But for in ground plantings, vinegar in the long run will not change the pH one bit.

Ammonium Sulfate will acidify the soil over time. It is not recommended in areas that have acidic soil because it will make them even more acidic. If the soil is alkaline, it can be hard to get the pH to change even with sulfur. Clay is harder to change pH than sandy soils.

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according to this, it’s got boric acid in it.

not sure if it’s there to supply boron, or to acidify, but nothing else in the ingredients will make the soil acidic.

But regular miracle gro has boric acid too.

I can’t really see any difference in ingredients, other than differences in the NPK levels.

It’s only there for Borate. Check out the concentration.

I missed the fact there is a higher percentage urea nitrogen in Miracid. Still not sure how much it helps acid loving plants…more of a marketing gimmick if you ask me. Drew, yes, you are correct about the vinegar. That’s where I learned about it, using it on my container blueberries. I’m not really trying to acidify the soil. My native sand/soil is pretty acidic, but the planting hole for my citrus has some garden soil in it, and I was just trying to help out the roots a bit until they reach the “good” soil.

in the case of blueberries nitrate nitrogen sources can be toxic. Urea is preferred. May not be true of all acid loving plants but honestly blueberries azaleas etc are the only plants Miracle grow cares about.

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They like Urea, but it is not acidifying. I was thinking of using it because in containers I have a problem with them being too acidic. They are in peat and pine, and if you add sulfur every time you fertilize, your going to kill your plant. I know, I have done it. So urea is a good alternative to feed them when pH is low enough. I have some right now that are below 4.0. I have been using tap water on them to knock the pH up.
Some acid loving plants just prefer acid, but can grow in basic soils, they are all different.

Been using some cheesy sulfuric acid I got at Ace Hardware to acidify my water, “Liquid Fire” brand. Paradoxically, I wouldn’t think of using something like that for its intended purpose of unclogging pipes.

Three capfuls to a 1.75 liter glass bottle (put water in bottle first, of course,) yields a solution five capfuls of which will take a five gallon bucket of my tapwater down to 5.5 or 5.0. Basically, acid rain. That way it’s not life-threatening.

The form of N and the fate of N in the soil-plant system is probably the major driver of changes in soil pH in agricultural systems. Nitrogen can be added to soils in many forms, but the predominant forms of fertilizer N used are urea (CO(NH2)2), monoammonium phosphate (NH4H2PO4), diammonium phosphate ((NH4)2HPO4), ammonium nitrate (NH4NO3), calcium ammonium nitrate (CaCO3+NH4(NO3)) ammonium sulfate ((NH4)2SO4), urea ammonium nitrate (a mixture of urea and ammonium nitrate) and ammonium polyphosphate ([NH4PO3]n).

The key molecules of N in terms of changes in soil pH are the uncharged urea molecule ([CO(NH2)2]0), the cation ammonium (NH4+) and the anion nitrate (NO3-). The conversion of N from one form to the other involves the generation or consumption of acidity, , and the uptake of urea, ammonium or nitrate by plants will also affect acidity of soil. Ammonium-based fertilizers will acidify soil as they generate two H+ions for each ammonium molecule nitrified to nitrate. The extent of acidification depends on whether the nitrate produced from ammonium is leached or is taken up by plants. If nitrate is taken up by plants the net acidification per molecule of ammonium is halved compared to the scenario when nitrate is leached. Bottom line, there is a whole lot of chemistry going on that isn’t obvious on the label.


I clipped the previous comment from a crop nutrition post just to make a point. There is an interaction going on between plants and soils that is a specific chemistry. While it is certainly possible to acidify soils directly with any kind of acid, this will not accomplish the mission of growing healthy plants… sort of like putting vinegar in an acid battery. Soil acidification will occur naturally if plants are receiving proper nutrients for their chemistry. This is why you don’t see an acid specifically listed in the ingredients of fertilizers for acid loving plants. The fertilizer contains ingredients which will acidify the soil as the plants absorb ions from the ingredients, leaving behind hydrogen ions to form those acids.

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Acid is often used in commercial settings, and it has it’s uses in agriculture and horticultural. True it’s an acid not a fertilizer. Most pesticides not all have a much longer half life if mixed in an acidic solution of water. As much as 30 times more effective. So yeah we have a lot of chemistry going on in horticulture. I use acids in breeding Rubus species ie brambles.
Often plant seeds require digestion or burning to germinate. Having a specialized seed coating that needs to be breeched. Acid works well! Acids are often used in hydroponic settings to control nutrient feed pH.
I keep sulfuric acid around for breeding, I used to use it for pH adjustments, but found safer ways to accomplish what I needed there. I like to use plain vinegar for pesticides to keep the water acidic. When possible I use rain water to mix with pesticides. My rainwater is at 5.0, which is about perfect.