Lower Soil pH

Dave289August 15, 2014

I just checked my Soil pH on my organic raised bed garden and found it to be 8! The other NKP levels were reasonable.No wonder my plants didn't do so well this year, probably a lack of Iron & Zinc? Unfortunately, I had been adding Lime for the tomatoes, which only made things worse. The question is, I would like to do my fall planting ASAP. Is there a way to move the soil pH lower, at least 1/2 a point before I replant? The rest of the change can be made over the winter, I would assume.

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Lime, Calcium Carbonate or Dolomitic Lime (Calcium Magnesium Carbonate) is used in soil to raise a soils pH and should only be added to soils if a good reliable soil test indicates the need and only in amounts suggested by the testing lab. Contact your local Virginia Tech Cooperative Extension Service office and have a good reliable soil test done and they will be able to help you with what and how much of the what might be needed.
Tomatoes need Ca and Mg in balance but in a soil with a pH in the 6.2 to 6.8 range. Adding Lime, or anything else, in the hope of preventing Blossom End Rot without a good reliable soil to guide what and how much to add simply creates more problems.

Here is a link that might be useful: Virginia Tech CES

    Bookmark   August 16, 2014 at 6:48AM
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toxcrusadr(Zone 6a - MO)

None of which answers Dave's question. Sulfur will lower pH but it takes some time, weeks to months, as it has to be metabolized by soil bacteria first. But you could certainly add it before planting.

For faster response you might consider aluminum sulfate or iron chloride, dissolved in water.They will rapidly affect pH. The first is used often on hydrangeas to change the color; the iron is usually used for iron deficiency but is also acidic.

If we had a nickel for every gardener who added lime without knowing their pH first, because someone said it was good... :-]

I don't know what your soil is like of course but if it's not already high in organic matter, add some compost too. It helps to bring pH toward neutral, and also a good rich soil will still grow good plants even if the pH is a bit out of the ideal range.

    Bookmark   August 18, 2014 at 2:02PM
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Aluminum sulfate is not as fast acting an amendment as most folks think. It is still recommended to apply 6 months ahead of desired planting time. A pH of 8.0 is not horrendous - I'd go ahead and use whatever you think best to lower pH for next season and try acidifying your irrigation water for any fall crops. That should provide a more immediate impact. Just a couple or tablespoons of regular table vinegar to a gallon of water. (this is typically a recommendation offered to those growing acid-loving plants in areas with alkaline water supplies).

I agree with tox..........if I had a dime for every time someone thinks they need to lime their soil or their lawn without verifying by soil test that such a practice is necessary, I would be a very rich woman :-))

    Bookmark   August 18, 2014 at 2:27PM
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Same concept applies to lowering the soils pH. Never add any substance without a good reliable soil test and a guide to how much of whatever is needed to reach the desired pH level.
Depending in where in the world you are adding two tablespoons of Vinegar to a gallon of water probably will not change the pH of that water much, as I recall from Chemistry class (a long time ago) the litmus paper did not change when that was done. We added closer to 50 percent Vinegar or a half gallon Vinegar to a half gallon of water to lower the waters pH enough to make much difference. The makers of injectors for commercial orchards that need to acidify water suggest using Muriatic or Sulfuric Acid. But that will depend on what the starting pH of your water is.

    Bookmark   August 19, 2014 at 6:43AM
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Even though sulpher is said to take a long time for full effect, I have found that I have measurable results in about 2 weeks. One of the things that happens is that the soil right next to the sulpher that was deposited has the pH of the local solution lowered; plant roots that explore that particular area will then be able to harvest some of the micronutrients that would otherwise not be available. I also highly recommend adding either compost, or even raw organic matter such as wood chips since they do help buffer the soil chemistry, and make nutrients more stablely available.

    Bookmark   August 19, 2014 at 12:39PM
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toxcrusadr(Zone 6a - MO)

Vinegar has a pH of about 2.5 A 50% solution (using distilled water) would still be under 3. It will likely be higher if the water has any hardness at all, but I can't imagine that plants can live in a 50% solution of vinegar. However, since you can apparently measure pH, all you have to do is mix the two up to find out. I'd start with 1/4 cup per gallon and test the pH. The high pH soil will react with it, but still, it's probably not good to go too far below the ideal range for plants so you don't shock or burn them. I'm thinking you want water at about pH 4 or 5. Anyone else have a recommendation? I'm just flying by the seat of my lab coat.

    Bookmark   August 19, 2014 at 6:07PM
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I would say add iron sulfate or sulfur (a combo is best) at the recommended rates to lower the pH by 1 point. You can look this up online - there are charts that give you approximate amounts depending on your soil type. Since your fall crops are likely to be Brassicas and/or in the beets/spinach/chard family, all of which are tolerant of alkalinity, I wouldn't worry about immediately lowering the pH for them.

I started with a pH of 8.3 this spring (thanks to the last owner dumping wood ashes into the soil). I had tilled in sulfur the previous fall but it obviously hadn't done anything yet. The spring crop of beets and turnips grew luxuriantly. By June, the pH had dropped to the high 7s but the subsequent crop of nightshades looked very chlorotic because it was still way too alkaline for them. They gradually got better over the summer as the pH dropped.

This post was edited by Slimy_Okra on Tue, Aug 19, 14 at 20:16

    Bookmark   August 19, 2014 at 8:10PM
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Many times I have seen people add sulfur, or lime, to the soil and then state that it did not do any good. When I ask how much did they apply it is something around 50 pounds over 5,000 square feet which may not be nearly enough if the soil needs 200 pounds per 5,000 square feet.
A good reliable soil test will give that information. By the same token, adding 200 pounds per 5,000 square feet when only 50 pounds is needed is a waste of time, energy, and money.

    Bookmark   August 20, 2014 at 10:27AM
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^Like I said, OP needs to add the amount appropriate to his/her soil type. Assuming that the initial pH measurement was accurate, knowing the soil type is enough to estimate how much sulfur is necessary. These charts are available online.

    Bookmark   August 20, 2014 at 11:42PM
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Phosphoric acid, nitric (muriatic) acid, sulfuric acid or citric acid are used to lower pH of water. Vinegar is too weak because high pH water is buffered by minerals.
Food Grade Phosphoric Acid is used in commercial greenhouse operations.
Although no acid is "safe" and all must be handled with care, nitric and sulphuric acid are dangerous. Citric is expensive.
Food Grade Phosphoric Acid adds phosphorus, ppm, to the water. If the water is very hard or a person is using triple phosphate fertilizers then care must be taken not to exceed the plant limits.
Water hardness and pH are related but not the same. pH is a measure of the acid or base. Hardness is a measure of the buffering ability of the dissolved minerals in the water. The type and quantity of dissolved minerals in some water requires more acid to lower the pH than water that might have a different mineral composition.
The people over at the hydroponic forum can be very helpful for specific questions about water pH, raising and lowering.

This post was edited by lucky123 on Thu, Aug 21, 14 at 0:11

    Bookmark   August 21, 2014 at 12:02AM
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toxcrusadr(Zone 6a - MO)

I agree with everything except that vinegar is too weak to counteract hard alkaline water. Use enough of it and it will. I'm not advocating one way or another on vinegar here, but if I had plants doing poorly that needed an immediate pH drop in their vicinity, I might consider it - again, with pH meter in hand.

Used to have a blueberry farmer here whose bushes were on a slope of heavy limestone based silty clay. Soil pH is about neutral around here. He had a wellhouse at the top, and would bring up water, amend with food and acid, and gravity feed the entire field through drip irrigators. His blueberries were legendary. Unfortunately I don't know what he used for acid. But those concentrated mineral acids you mention - phosphoric, sulfuric, nitric, hydrochloric - are strong stuff, and only takes a smidgeon.

    Bookmark   August 21, 2014 at 12:57PM
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tishtoshnm Zone 6/NM

One thing I learned recently, is that it is important to find out why your pH is high because some higher pH soils will take a very long time to lower the pH. My soil is limestone based, and the aquifer my water comes from has a lot of limestone in it. Knowing this means I need to pay attention to what rootstock my roses are on and not to waste money on other treatments that will not work. The University of Colorado has some good information for my type of soil. Find out your type of soil before spending money that will be wasted.

    Bookmark   August 21, 2014 at 1:21PM
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It is a very small amount. I have 40% concentrate phosphoric acid. I add 2 oz to 1 gallon water. Then I add 10 drops from the diluted gallon to 1 quart water. That is a "Smidgeon."
Someone else might have to add more or less drops depending on hardness. I use the paper pH strips to test the water.
The diluted 1 gallon of water/acid is fairly safe to handle but I am careful with it. The diluted quart is absolutely safe and treated as plain water.
The acids, phosphoric, nitric, sulfuric are all very dangerous in concentration and should be handled with care. Absolute Rule -Always add acid to water. Review all safety precautions every time you handle acids. For amending water, it is a seldom thing and easy to forget all the safety rules. Wear chemical gloves and eye protection. Store and dispose of acids properly.
Vinegar will work, but it will not hold the pH, from what I have heard.

This post was edited by lucky123 on Thu, Aug 21, 14 at 13:46

    Bookmark   August 21, 2014 at 1:42PM
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Citric acid, like vinegar, also fails to hold the pH since bacteria will eventually oxidize it to carbon dioxide. But both are good choices as interim measures to bring the pH down for crops already in the soil.

    Bookmark   August 21, 2014 at 8:30PM
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The U. S, Geological Service has mapped the pH of water throughout the USA. This map may be of some use to some people.

Here is a link that might be useful: pH of water

    Bookmark   August 22, 2014 at 6:18AM
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drew51 SE MI Z5b/6a

I usually don't post in this forum. I grow blueberries. Vinegar and citric acid break down too quick. I would not use them. I use sulfuric acid in my water. You can get a safer and easier to work with solution by using battery acid obtained at any auto supply place. Myths about impurities are not true, else your batteries would explode! It's 30% sulfuric acid, it will burn, but is safer. Use gloves and safety glasses. Easy pour spout too!
Espoma makes a good soil acidifier, and Iron-tone.
Ammonium sulfate, not aluminum will lower your PH quickly! It's cheap. I use 1 teaspoon for 2.5 gallons. A very safe amount.
You could also use an acidic fertilizer for awhile like Holly-Tone. Has sulfur, slow to work. Cottonseed meal is also excellent. I maintain a PH of about 4.5 for my blueberries. Results are in hand

    Bookmark   August 22, 2014 at 6:49AM
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Using Madison(Wisconsin) City water, which has pH = 7.6, it takes 12 fluid ounces of 5% white vinegar, per 4 gallons of water, to lower the pH to 5. Drenching the soil with a solution such as this will immediately lower soil pH, however, vinegar is an organic acid, and it is slowly consumed by soil bacteria, so the pH of the soil will eventually rise. Since vinegar can be used to kill weeds, clearly there is such a thing as "too much acid," and it should be used with care. In the past I have used vinegar solutions to lower soil pH around our blueberry shrubs, but now I am using agricultural sulfur for this purpose. The sulfur requires more time to take effect, and it keeps the pH down for several years. I still have to test soil pH, once a year.

    Bookmark   August 22, 2014 at 10:43AM
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toxcrusadr(Zone 6a - MO)

All good posts, I have little to add except:

Aluminum sulfate *is* sold for ag use but apparently if you use too much, aluminum toxicity can develop. I don't know how much is too much. OTOH ammonium sulfate is also a nitrogen fertilizer (perhaps that goes w/o saying but just so we're clear). You would want to be careful with soluble nitrogen as well so as not to burn plants.

    Bookmark   August 22, 2014 at 4:48PM
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