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Mixing acid with wood ashes for fertilizer...

Posted by fabaceae_native z6 NM (My Page) on
Sun, Dec 11, 11 at 13:35

I would love to use the ashes from my wood stove. I have held off using them because the soil here tends toward being alkaline.

What about neutralizing the ashes with acid, either vinegar (acetic acid) or hydrochloric? I have had enough chemistry classes to understand that the acid will react with the ash to produce potassium and calcium salts which are both extensively used as fertilizer.

I've scoured the internet for evidence that this can be done without raising the soil pH the way raw ashes would, but have found nothing. Anybody have an idea about this?

Thanks for any thoughts...


Follow-Up Postings:

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RE: Mixing acid with wood ashes for fertilizer...

Vinegar would make calcium and potassium acetate, of course. I have no idea how sensitive plants are to acetates. Muriatic (pool acid and concrete cleaning acid) is easy to find relatively inexpensively, but the chlorides it makes will have to be highy dilute on the plants. Sulfuric acid would be best, as it makes gypsum and potassium sulfate, both used as fertilizers.

Why not thinnly layer or intermix it with ag sulfur and organic debris in a special compost pile and use it in a year? It would take a little figuring as to proportions ash:sulfur but that would not be too hard. The approximate ash chemistry is easy to look up.


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RE: Mixing acid with wood ashes for fertilizer...

While I have been known to tell people that adding wood ashes to soils, or compost, is not a good idea I also know that the soils around San Diego, Ca. benefit from adding Calcitic lime. Every university article about using wood ashes always says to have your soil tested before adding those wood ashes. Whether adding your ashes would be more harmful or possibly beneficial will depend on why your soil tends to be alkaline.
It is less about what is in the ash then what is in your soil. Simply knowing that your soils pH is 7.8 is not enough. You need to know why it is 7.8.


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RE: Mixing acid with wood ashes for fertilizer...

I am going to hazard a guess, but zone 6, New Mexico (which is what I am), the soil is likely alkaline due to limestone, likely further aggravated by hardwater. DH is more acquainted with the rocks of this area but I think limestone runs throughout this area.


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RE: Mixing acid with wood ashes for fertilizer...

I'm not sure what it will do to your PH. But 2 years ago last spring I burned a huge pile of hardwood tree limbs that I had piled up in the old pasture, about 20' in diameter and 10' high.

Since it killed all of the grass and weeds I decided to stick some extra watermelon seeds that I had on hand in the bare spot. No tilling or fertilizer.

I had bigger, sweeter, and earlier watermelons than the ones in my garden.


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RE: Mixing acid with wood ashes for fertilizer...

Wood ash is high in potassium, pH above 10. NPK ratio is 0-1-5 ...compared this to acidic oak leaves, pH 3-4, NPK of 0.8, 0.35, 0.15.

Mix the above two, wood-ash and leaves, would make a harmless neutral combo. That's what my Mom did in Michigan for 35+ years, but she kept wood ash away from plant roots - she threw wood ash on top of leaves. I tested both wood ash and oak leaves in red cabbage juice: wood ash turned the juice 100% green immediately. It's MUCH more alkaline than baking soda. Oak leaves turned the cabbage juice from purple to pink (like vinegar). After many days, the solution changed from pink to brown (I suspect leaves act as a buffer).

Kimmsr wrote about wood ash screwing up the composting process. I found some info. on raising pH and compost : Myth #5: Adding lime can benefit your compost. "There is never a need to add lime to a compost pile. It can actually make things worse. Compost goes through natural pH changes, including an acidic stage while the pile is active. A sudden rise in pH from adding lime can actually kill a whole generation of beneficial organisms. Lime also has the disadvantage of releasing and losing valuable nitrogen, which can actually create a foul ammonia smell. Lime may be added to acidic soils, but it serves no beneficial purpose in the compost pile."

Here is a link that might be useful: 13 Common Composting Myths


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I think it's a great idea,, fabaceae !

I like your idea of mixing wood ash with vinegar to add potassium and calcium to the soil. The soil testing company EarthCo. that tested my soil stated "1/3 of the soils we tested are deficient in potassium". I thought my soil is high in calcium - I'm next to a limestone quarry, but my soil tested barely adequate in calcium, but super-high in magnesium.

I checked the blueberry forum for info. on making my pH 7.7 soil less alkaline and found: ammonium sulphate in soluble fertilizer acts quickly, but applying sulphur to the soil takes at least 6 months. Most tap water are alkaline: I have well water, mine tested at 8 using fish tank litmus paper (it gave distilled water a 7, and bottled water a 7.5). City water is also MADE alkaline so it doesn't corrode pipes.

It was OK for my Mom to throw wood-ash in her garden since there's lots of rain and snow in Michigan, and she NEVER water her garden. Could it be that the more acidic rain water neutralize the ash overtime? But for someone in a dry area using wood ash and tap water for their garden, it's a different story.


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RE: Mixing acid with wood ashes for fertilizer...

Keep in mind that wood ash is primarily Calcium Carbonate, lime. While wood ash does contain other mineral nutrients the amounts are really quite small.

Here is a link that might be useful: Nutrients in wood ash


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RE: Mixing acid with wood ashes for fertilizer...

New Mexico is probably a bad place to add anything alkaline, I would agree with that.

The original question was how to neutralize it. The only way you will know when you reach the proper spot on the pH scale is doing it quantitatively, by titration. If you have a pH meter you can do it. Take a standard amount of ash - 1/2 cup, for example - and mix with a quart of water to make a solution. Then add acid slowly, measuring as you go, and watch the pH. You can then calculate (if you remember your algebra) how much acid it will take to neutralize 10 lb or 5 gallons (or whatever) of ash.

If you end up using a concentrated acid like hydrochloric, 1) be VERY careful with that stuff and 2) it may be easier to handle/measure if you dilute it somewhat with water. Like 50/50. This way you might not have to try to measure 1/16 of a teaspoon for your experiment. Always acid to water, never the other way around, and wear protective gear.

It would actually be best to do it in a water slurry anyway, in a big bucket, to ensure you get complete mixing, and apply it to the ground that way. It will cover more evenly that way.

Not saying this is a good idea, because of some of the issues raised above about the effects of the various salts, but this is how you can do it.


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RE: Mixing acid with wood ashes for fertilizer...

Check out Titration - Wikipedia, the free encyclopedia. It looks quite informative.


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RE: Mixing acid with wood ashes for fertilizer...

Thanks for all the feedback. The soils in Santa Fe are from granite, no limestone in the area, but the higher pH tendency (mine is about neutral) is I believe still caused by calcium carbonate that is not readily leached out because of the aridity.

I realize that lime is the major constituent of wood ashes, which is precisely why I have not been using it on the soil, but I guess my question is if the form of calcium produced by the acid reaction will be any better? Calcium sulfate (gypsum) is an important fertilizer, as gonebananas points out, and sulfur is used to lower pH after all. Gypsum is used to improve hard packed saline soils (which are probably alkaline as well?).

I guess I just have my work cut out for me: getting my soil tested, then experimenting with the wood ash mixture in a small area and re-testing.


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Calcium Citrate tested neutral in red cabbage juice

Someone in this soil forum pointed out that magnesium in sticky clay soil is what raises the pH, and NOT calcium. Calcium citrate supplement does NOT require acid to dissolve like calcium carbonate - so I tested calcium citrate in red cabbage juice. There was absolutely no change in color. But when I dissolved magnesium oxide and stearate (from magnesium supplement) in red cabbage juice - it turned bright GREEN (very alkaline).

That explains why my soil is loaded with limestones, but my soil test revealed barely adequate calcium level, and super-high in magnesium. That gypsum stuff is expensive, $5 for a tiny bag from Menards - so if you can get calcium out of wood ash, that's great.

For $20 - EarthCo. at www.drgoodearth.com gives you a basic soil test (pH, organic matter, phosphorus, potassium, calcium, and magnesium) and for $30 they give you the whole package plus analysis of trace minerals. You send it 1 cup of soil, and they e-mail you the result within 2 weeks. The best part is the booklet that they give you, which explains the basics of soil. They also show what's high or low, and how to fix it.

Thank you kimmsr and albert for those links - I learn so much from you guys - much appreciated.


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RE: Mixing acid with wood ashes for fertilizer...

I have a couple of comments here.

"Someone in this soil forum pointed out that magnesium in sticky clay soil is what raises the pH, and NOT calcium."

This I am not sure about, not having the actual text in front of me. I would think MgC03 would raise pH just as well as CaC03 - because it's the carbonate that raises the pH, not the metal.

"Calcium citrate supplement does NOT require acid to dissolve like calcium carbonate - so I tested calcium citrate in red cabbage juice. There was absolutely no change in color. But when I dissolved magnesium oxide and stearate (from magnesium supplement) in red cabbage juice - it turned bright GREEN (very alkaline). "

Well, yes, calcium citrate is a salt, so there is little to no change in pH when you add it to water. Whereas mag. oxide is a strong base - MgO reacts with water to produce Mg++ and lots of OH--, raising the pH. Calcium oxide would do exactly the same thing, and similarly, magnesium citrate would show no pH change just like the calcium citrate. Mg and Ca act very similarly, it's what they're combined with that is giving you those results.

"That explains why my soil is loaded with limestones, but my soil test revealed barely adequate calcium level, and super-high in magnesium."

This one I'll leave for the soil scientists here to comment on.

"That gypsum stuff is expensive, $5 for a tiny bag from Menards - so if you can get calcium out of wood ash, that's great."

I'm surprised it would be that expensive, it should be about as cheap as lime. The calcium from ash would only become gypsum if combined with sulfuric acid to make calcium sulfate. So vinegar or muriatic (hydrochloric) acid added to ash will not make gypsum. Just FYI.

"For $20 - EarthCo. at www.drgoodearth.com gives you a basic soil test (pH, organic matter, phosphorus, potassium, calcium, and magnesium) and for $30 they give you the whole package plus analysis of trace minerals."

I would recommend always looking at your local County Ag Extension office (here in the US), which do the same tests for a comparable or lower price, no shipping cost, and are more familiar with local soils. If you don't have a local resource I'm sure EarthCo is fine, I'm just all about using local resources that your tax dollars pay for.


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RE: Mixing acid with wood ashes for fertilizer...

"That explains why my soil is loaded with limestones, but my soil test revealed barely adequate calcium level, and super-high in magnesium."

I've been trying for a while now and I still can't quite figure out what the claim is here.

(nice job on the rest, Tox)


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RE: Mixing acid with wood ashes for fertilizer...

Well, here in New Mexico I can get a large bag of gypsum for about $5 at Wal-Mart.

One thing I would consider is whether or not it is worth it. If you like to experiment, have fun, but, if I were evaluating this, I would consider the fact of spending money to make the wood ash usable where as I could spend my money on other things for the garden. This year I am dumping my wood stove cleanings in the drainage along my driveway. For fun, I may experiment with planting some seeds in it but that will be my experiment zone. If you experiment, please tell us how it goes. Good luck!


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RE: Mixing acid with wood ashes for fertilizer...

Thank you, tishtoshnm for info. about cheaper gypsum from Walmart. Thank you, toxcrusadr, for clarifying and reminding me of what I forgot in chemistry classes. My county extension soil test is more expensive and does not test for calcium nor magnesium.

I begin to question the much-more magnesium than calcium result from EarthCo. soil test ... I'm next to a limestone quarry. My roses don't have rust, nor ball in the rain - symptoms that exist in a calcium-deficient soil. I don't have fruit rot at the bottom of my tomatoes either. It may not be necessary for me to add gypsum to roses' planting holes as instructed.

Tishtoshnm: Let me know how your experiment goes planting seeds on wood ash. In the Orchards Forum, it mentioned epsom salt as NOT effective for bigger plant nor bigger blooms, but it's effective in seed germination. Epsom salt is magnesium sulfate. In my high magnesium soil, I spend most of my gardening time pulling baby perennials that sprout all over the lawn: summer phlox, black-eyed susan, tons of dandelions, Rose of Sharon, baby unwanted trees. I give up on perennials and plant roses, since they don't seed and sprout on my lawn.


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Is wood ash caustic like lime sulfur?

In the old days, agriculture used lime sulfur to control mildew and rust. Info. on lime sulfur gave: "Safety goggles and gloves should be worn while handling lime sulfur. Lime sulfur solutions are strongly alkaline (typical commercial concentrates have a pH over 11.5), and so it is corrosive to living things and can cause blindness if splashed in the eyes." Would wood-ash burn the skin and eyes too?


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RE: Mixing acid with wood ashes for fertilizer...

I agree, tishtoshnm, gypsum is cheap, and it doesn't make much sense to spend a bunch of money on making the wood ash useable (although I think using sulfuric acid would be quite inexpensive). It's just something I've always wondered about.

I never knew it could be something other than calcium carbonate raising the soil pH, but I definitely have a sticky clay soil -- maybe it is the magnesium.

Well, thanks for the input. I will post again if I get any interesting results on this subject.


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RE: Mixing acid with wood ashes for fertilizer...

Wood ash would definitely be an irritant if the dust were inhaled or if a liquid suspension was splashed in the eyes. I've gotten a sinus headache from fussing with dry ash and inhaling to much. A dust mask is in order for that, and a very slight breeze can help carry it away.

As far as skin, it would be an irritant similar to lye. If you've ever gotten a strongly alkaline solution like that on your hands, it feels slippery as you try to rinse it off. Fresh cement is that way also. They say that's the hydroxide saponifying fats in your skin - in other words turning you into soap just a little bit. :-o

Reasonable protection is all you need, maybe some rubber gloves, goggles or at least glasses, and old work clothes. No different from handling strong cleaning products, bleach, etc.


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RE: Mixing acid with wood ashes for fertilizer...

Wood ashes are an excellent source of potassium, calcium and minors. See: Best Management Practices for Wood Ash Used as an Agricultural ... They report a much higher crop yield using ashes over lime. And yes, you will get calcium acetate and potassium acetate if you neutralize ashes with vinegar. Calcium acetate is sold as Foli-Cal to treat blossom end rot in tomatoes. Potassium acetate can be applied as a spray.
Wood ash was the principle currency during the colonial period. The first US patent by Samuel Hopkins detailed converting potassium hydroxide (potash) in to potassium carbonate (pearl ash).

Here is a link that might be useful: Best Practices for Wood Ash


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RE: Mixing acid with wood ashes for fertilizer...

Look at the potash link in Wikipedia.

Here is a link that might be useful: Potash


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