lowering my soil pH organically, will citrus work?

cabrita(9b SoCal)March 17, 2009

This is my first question to this forum. I found out I am a little higher than ideal pH wise (about 7.4, it varies a little from area to area, but alkaline) to grow my beloved solenaceas (mostly tomatoes). Also, my soil is deficient in potassium. Nitrogen is really high and Phosphorus is adequate. My soil texture is great, got worms, and a lot of naturally occurring granite and other minerals.

I also have a lot of citrus peels that I try to compost (it is hard though, isn't it? they do take a very long time to compost) as well as citrus branches, and juice from immature fruit from pruning.

For adding potassium, I have a lot of hardwood branches that I was going to burn. I know the pH from the ashes will be high (like 8 maybe??) and not a good thing for me to try to lower my pH, but I need the potassium for my soil. What if I burn the wood, soak the ashes, measure the pH, and add enough citrus juice to render it neutral? or slightly acidic? I mean, lemon juice has a pH of 2, right? so this should work? Then add that to my soil. Anything wrong with this strategy?

Also, would there be any harm in introducing some of my excess citrus juice (the green ones mostly) diluted with water to lower my soil pH around the plants that need it? I know it would be temporary, but isn't any pH changing method temporary anyway?

I used a bag of sulfur but that went away really fast, it was expensive, and did not change the pH that much.

What about ground up citrus peels added to the soil? would that have better long term effects on pH? I know oak leaves and pine leaves are supposed to help, so i will try to get those into the compost bin when I can find some. The citrus is easy though, all around me, free, and more than we can eat/drink.

Thanks for any advice or information you folks might have on this.

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I dunno whether citrus peels will acidify soil or not, but if sulfur was used and it didn't reduce pH there is something going on.

In terms of short term reductions, it is more common/tested to use sulfuric acid in irrigation water (very dilute). A much safer approach for a home gardener is to add an ounce or 3 to a gallon of water. Safe effect. This simply acidifies the water around the plant roots very temporarily, but allows for better nutrient uptake when used regularly.

I wonder how you are determining your pH and nutrient levels? Did an actual lab do the test or are you using home test kits? If home test kits, get a lab test done please to confirm your results before adding another bag of sulfur or anything else.

I don't know how much 'a bag of sulfur' means in your case, but odds are it was more than enough to do what you needed it to, over time. No, the effect isn't permanent, but certainly lasts awhile.

    Bookmark   March 17, 2009 at 4:29PM
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Dan Staley

I don't know how much 'a bag of sulfur' means in your case, but odds are it was more than enough to do what you needed it to, over time. No, the effect isn't permanent, but certainly lasts awhile.

I agree with jag.

The "bag", provided directions were followed, should have done it. Citrus will not. Keep the peels out of the garden soil and put in your compost, so they can break down next year or so.

There is no reason that sulfur cannot be used in an organic garden, and if you want to feel better, buy one with 'natural' or 'organic' on the package; I also can't see why an iron sulfate couldn't be used as well. I can't picture in my mind why the HAc from citrus juice wouldn't free up H+, but the pH is generally around 4-something, and personally I wouldn't put something that low near my roots.

You can add potash by using greensand, which will do the job a lot faster than the method proposed above, not adversely affect your pH or solum, and persist in the soil for a reasonable time.

I also agree that a $2.00 soil test likely isn't an accurate indicator of soil chemistry, and hopefully a representative sample was sent to a lab, and they gave recommendations with the analysis.

Good luck.


    Bookmark   March 17, 2009 at 4:49PM
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Burning any organic matter cause a loss of more valuable nutrients than it creates and produces very large quantities of pollutants, it is never a good idea to burn organic matter except to produce needed heat.
Citrus will not significantly change your soils pH any more than Oak leaves, Pine needles, or peat moss will. A soil pH of 7.4, not that much higher than the optimal 6.2 to 6.8, would be of less concern than that very high Nitrogen that will produce a lot of lush green gowth that would be very attractive to insect pests and limit the plants ability to produce fruits. I would add some high carbon material to the soil which can reduce the N, as the soil bacteria work at digesting it, and probably add some
Potassium as well.

    Bookmark   March 17, 2009 at 7:23PM
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I used a bag of sulfur but that went away really fast, it was expensive, and did not change the pH that much.

Was it a 5 lb. bag or a 50 lb. bag. How large was the area?
Did you just broadcast it or till it in. If you just spread it on top, the effect will be virtually nothing below a centimeter or two, even in a sandy soil.
How long after you applied it did you measure your pH? That change can take a very long time (months or even years). The amount of change you get and the time it takes depends on, among other things, your soil's ability to resist that change, aka "buffering capacity". The higher the clay content and lime content and organic percentage the higher the buffering capacity. Temperature is also a big factor. The change is largely due to the activity of microbes that are more active when temperatures are warm.
And finally, Sure, tomatoes (like just about everything else) would prefer a slightly acid soil reaction, but they should be just dandy at a pH of 7.4. (I too share the concerns about what type of test was used)

    Bookmark   March 18, 2009 at 9:27AM
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cabrita(9b SoCal)

Thanks for all the input!

The soil test was done by us but it confirms what we observed: lush green growth on the cole crops, not so good for fruit size, mint does great (mint need alkaline soil to grow). Also we got a little garden pH meter and we get the same readings we did with the color coded tests. I will not bother with a professional soil test. I inquired about getting one but it is too expensive! I would need to send samples from different portions of the garden, our university extension does not provide this service, and the cost to us would be $120 per sample from the lab they recommend. Do you know how many seedlings and seeds I can buy with $120? also, I am trying to keep my tomatoes under $50 a piece....LOL. Besides, we like to be able to add some amendments and re-test, so we see if we are the getting the changes in the right direction at least.

I do not see what is the difference between using sulfuric acid, which concentrated has a super low pH, than citrus juice, which I can dilute as well.

I think the bag of sulfur was about 10 lbs, it did drop the pH some, but did not go under 7. I did not know there was a delayed effect though, thanks for this information. I read that 6.8 is maximum for tomatoes. The tomatoes were really bad last year, so this is my main concern. Most other crops did very well though.

I was not sure how to solve the 'too much nitrogen' problem, so I used mulch type compost rather than my regular kitchen waste compost. I think that would have added some carbon instead of nitrogen, I hope it did anyway. Also, my partner added some peat moss, so I guess this also adds carbon (and lowers the pH), and adds organic matter to the soil. We are not quite done adding all amendments so we will do another test after everything is in the new beds soil.

    Bookmark   March 18, 2009 at 6:14PM
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cabrita: have you had a disapointing soil test or disapointing produce? If the answer is yes/no I would stop worrying and concentrate on adding compost and biological activity to your soil. Regards, Peter.

    Bookmark   March 18, 2009 at 6:38PM
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Dan Staley

I am in Colorado, home of alkaline soil. Sulfur is what we use out here. Iron sulfate too. Citrus? No. If you want to pour some acid on your soil, feel free, but I won't condone it. I started at the bottom of the beds with 7.8, which I thought made me lucky. Then 7.4. Then 7.2. Now at 6.8. Things don't happen overnight.

Good luck.


    Bookmark   March 18, 2009 at 8:27PM
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While home testing kits to measure pH can be moderately accurate (be sure you use distilled water!), the home test kits for nutrient levels are notoriously inaccurate. If you are going by the results of one of those, you are really just guessing as to the nutrient content of your soil and what may be lacking or present in too high a concentration. Forget anything they may reveal about nitrogen levels for one - even professional labs have difficulty in accurately assessing this nutrient as it is highly mobile in the soil and can change from day to day with changes in temperatures and moisture levels.

I am assuming you are located in California (Sunset zone 21?). A good many California soils tend towards the slightly alkaline side of the scale. And your your irrigation source is likely going to be alkaline as well. Given these conditions, I am thinking that 10# of sulfur was just not adequate to effect a significant change. To lower the pH of a standard loamy soil (not too sandy, not too clayish) from 7.5 to 6.5 you need at least 15# per 1000sf worked into a depth of 6-8 inches. And it does take time - the reaction is slow and I wouldn't expect to see much of change before 4-6 months.

I would also encourage you to have a professional soil test done at least once. This will give you an accurate baseline from which to measure nutrient requirements and possible amendments going forward. I agree $120 is a bit excessive but I've attached a link to a lab with offices in both Portland and Seattle that provides a comprehensive soil test for $50. And you don't need to do multiple samples - you just need to combine soils from representaive areas (where you plan to concentrate your plantings) into a single sample. It is truly worth the investment and will save you a lot of time, frustration and other needless expense second guessing those useless home tests.

btw, since the pH scale is logarithmic, there IS a significant difference between a pH of 7.4 and one that is mildly acidic, say 6.3-6.5......like 10 times more alkaline. No wonder your tomatoes were not happy.

Here is a link that might be useful: Soil and Plant Laboratory

    Bookmark   March 18, 2009 at 9:17PM
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You're in SoCal, right Cabrita? I agree you might get more acidity out of oak and pine litter than the citrus.

I've used diluted vinegar in situations were I quickly want a pH drop. Household vinegar as a spray is a pretty effective herbicide as well, and for exactly that reason you have to be careful with it around plants and dilute it sufficently around sensitive roots. But nothing wrong with dumping a bucket of vinegar water into an empty bed before planting the tomatoes.

    Bookmark   March 18, 2009 at 10:26PM
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You say that you have tested the soil with a "little garden pH meter". There is a trick to using these to ensure a correct reading. Lightly rub the prongs of the meter with a very fine sandpaper before every use. Makes a difference.

I do not know what it takes to get nurseries to stock Back to Nature organic cotton burr mulch. This is by far the best acidifier on the market. It comes out of Texas and can be found there, but is mostly unknown in the rest of the country. It also is helpful in breaking down clay soils.

    Bookmark   March 18, 2009 at 11:03PM
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Dan Staley

Gardengal, your comments are cogent but the paucity of information given by the OP makes this all guesswork. We might as well assume that 10# was spread over 4000 sf, as there is no acknowledgment of directions followed for anything.

I strongly suggest, from the content of the comments made by the OP, that a basic hort class be taken at the nearby community college, or at the very least the reading list be obtained and everything on the list get read. Please. Do your plants a favor.

Good luck.


    Bookmark   March 19, 2009 at 12:04AM
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There are many Soil Testing Labs that will give you what you need to know for between $9.00 and $15.00 dollars per sample, plus shipping. Some are Universities, like UMass, while others are private labs, but there is no reason to spend $120.00 to have a soil test done unless you need a lot of stuff tested and are a commercial grower.

    Bookmark   March 19, 2009 at 6:55AM
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cabrita(9b SoCal)

Well Dan, I am not sure so much condescension was necessary. It turns out that I have been growing ALL my fruits and vegetables, and ALL my herbs, for the last 3 years. No winter breaks. I have been getting production for 4 seasons, in just 1/4 of an acre. I do not have to buy vegetables/fruits at the store, period. I doubt everybody in this forum can say the same. My plants are doing very well thank you, and they have also been feeding me (and a few other people) abundantly.

The exception were the tomatoes, they still produced some, (and are still producing, there is one still alive and fruiting) but not nearly as well as the ones grown in a much poorer and clayish acidic soil in our former garden.

Thanks to all of you who offered helpful suggestions. I have enough information to proceed, but feel free to continue the discussion.

    Bookmark   March 19, 2009 at 3:40PM
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Dan Staley

Cabrita, my comments were meant as blunt constructive criticism, I'm sorry you took them otherwise. There are enough clues in your comments that were you to understand soil and plants, your production would be much higher, feeding more people with less effort. Good luck in your effort.


    Bookmark   March 19, 2009 at 8:53PM
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Everyone should take advantage of the types of classes recommed by Dan every 5-10 years. Things change in gardening and most want to keep up with the latest information.

This said not all instructors are current with information or know of variations of plants. Too many times I have been advised to pull up green beans and replant by instuctors. Apparently many are not aware that if the plants are healthy, leave them and they will keep baring until frost. Also listen to the crackpots that showup even if you don't learn something you have after dinner conversation material for a while. Many times they have more usable stuff than the rest of the group.

    Bookmark   March 20, 2009 at 11:44PM
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I'm posting on this OLD post because it still comes up at the top of google search for "citrus peels lower soil ph" ...

I have been doing tests with Citrus Peels....
I have found that about 30 good size grapefruit peels blended up in a blender (lots of batches of blending) with half water/half citrus in the end, produces a good acid base.

I did enough to fill 30% of a 5 gallon bucket, which I then diluted to a full 5 gallons of liquid.

This was then diluted 5 fold to register a drop in pH of 1 for the water...

This diluted citric acid can be used similarly to sulfuric acid dilute. There is a company here that sells Moon Juice which is a combination of sulfuric acid + iron and other trace minerals... It's used for temporarily lowering the ph so trees and shrubs and such can uptake iron and other minerals that lock out at alkaline pH Levels...

Given that we're in the southwest we have an ABUNDAND supply of citrus and over time, this is the same effect the trees fruit would give to the soil if there were no humans to tend to and pick the fruit... the fruit would rot on the ground, the citric acid would leach out into the ground as it decomposes and maintain a more acidic soil balance for the trees long term support...

So can you use citric acid to dilute, yes you can, though, just like with a sulfuric acid dilute, you're going to need to apply it regularly (monthly or so depending on ph plant/etc) until the bacteria that feed on the sulfur have had enough time to lower the soils actual ph levels ...

Something that seems to be long forgotten as I read some of these posts is... all living things have a pH, you can burn things by dropping ph too fast, or by raising too fast, so obviously some of the responses regarding putting acid next to the roots are appropriate, they are also inappropriate because your obviously not going to dump straight acid on anything unless your intention is to utilize the full strength of the acid :P

Good Luck! Would love to hear about what you've done and how it's developed since your original questions!

    Bookmark   January 21, 2015 at 2:10PM
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Cabrita: I wish you the best with your tomatoes and other crops, my tomatoes always do fine in pH 7.2 soil but, that's my soil. I urge you to learn as much as you can from a laboratory soil test in order to understand and alter and/or amend your soil to achieve your goals. A simple example on changing pH in my soil - if I didn't know from a lab test that my soil was pH 7.2 and very calcareous, I wouldn't have a clue how much, if any sulfur to add to drop the pH a point. I also wouldn't know that adding sulfur would lead to soil dissolution, essentially, dissolving my soil, a bad thing.

Many soil labs can guide you on how to change your pH both with given materials and their rates. Contact the lab you want to use and request a soil sample submission and sampling and handling instructions form. A lousy sample will give you erroneous results at best. Usually, a lab's standard test will give you plenty of information, you can always add more analyses for more money.

    Bookmark   January 21, 2015 at 10:50PM
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The general answer for reducing alkalinity is sulfur or sulfates. So, if your soil test indicates a mineral deficiency, let's say calcium, then apply calcium sulfate, i.e. agricultural gypsum, or, if it's magnesium, then magnesium sulfate, i.e. Epsom salts. Use the amount of the mineral deficiency to determine how much to apply. Regards, Peter.

    Bookmark   January 22, 2015 at 12:05PM
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little_minnie(zone 4a)

I get 40# of sulfur from the local farm chemical store for $20. They generally just deal with farmers. I feel like a whore going in there for it with all the pesticides! It does lower ph but it creeps back up in a dry year when I irrigate a lot vs. get rain.

    Bookmark   January 22, 2015 at 3:45PM
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Well put Peter, I agree!

    Bookmark   January 23, 2015 at 9:09PM
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