I have a slightly high pH, 7.2. Nothing bad but I would like to bring it down a little. I was looking at two elements/products whatever you want to call them. One was Aluminum Sulfate and the other was Sulfur.

The things I know is it does not take near as much S to bring down pH, were it does take a lot of AlS.

But I do not know if there is anything wrong with AlS or S. I would really like to know the negative effects of either, if any. Thanks!

AlS - Aluminum Sulfate S - Sulfur

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    What are you trying to grow? Mar 14, 2018 at 18:12
  • I just remembered that you should test your pH when your soil is warm. Somewhere in the cobwebs of my brain is that pH reads more alkaline when it is cold, more acid when warm. I'll go look this up...so you might just be fine doing nothing.
    – stormy
    Mar 14, 2018 at 22:26
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    You are so close to neutral that when your soil warms up the pH goes down. Adding decomposed organic matter will also cause the pH to stay neutral. Your soil will be just fine for planting this spring. I would dump decomposed organic matter all over your soil now. Sprinkle with nitrogen, moisten and wait until spring to retest. In spring, you should make your beds with a shovel. Too wet now to make your beds even with a shovel because of clay. Have you put a cup of soil in a mason jar, shake, let settle to see the composition/percentages of soil particles in your soil?
    – stormy
    Mar 14, 2018 at 23:07
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    I've found pH to make a huge difference. Pacific NW instance get lots of water, clay soils, longer cooler springs all reducing the pH of the soil which makes Rhododendrons, Vaccinium (huckleberries, blue berries), azaleas very very happy. Unless they are planted by concrete foundations or walkways. Just the lime leaching from the concrete raises the pH in that location and otherwise happy Rhododendrons become anemic. Unable to uptake Iron without an acid pH.
    – stormy
    Mar 15, 2018 at 21:32
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    ...lawns need much more alkalinity than do most of the ericaceous plants of the PNW. Adding lime to raise that pH makes a spectacular difference. People tended to lime without testing first and were making concrete out of their lawn soil beds. Slight changes make huge differences in plant health. Plants in pots have no fungi, bacteria because their soil should have been sterilized. I plant potatoes in big pots using potting soil but the pH is 6.5 and potatoes like 5.5. I add sulfur, mix and plant potatoes two weeks later with cages and straw...what a difference in production and health!
    – stormy
    Mar 15, 2018 at 21:39

4 Answers 4


Lowering soil ph isn't a one off treatment - it needs to be ongoing, with frequent soil tests to check its not getting too low. Sulphur is the safest from a planting point of view, but takes longer to work in cold weather. Aluminium sulphate works more quickly, but its easy to overdose - it can build up in the soil to toxic levels, and reduces phosphorus levels, which can cause significant problems for plants. Sulphate of iron is sometimes used, and can create similar issues with phosphorus availability. Another factor is whether there is free lime or chalk in your soil - if there is, then attempts at lowering the ph are not likely to be successful. Information here https://www.rhs.org.uk/advice/profile?PID=82

Aluminium sulphate and sulphate of iron are usually applied around specific plants rather than applied to a whole area, the former often to produce bluer flowers in Hydrangea, and the latter for similar reasons and to correct leaf chlorosis in acid loving shrubs. You might want to consider finding plants that suit the soil you've got rather than trying to keep the ph lower ongoing if you were thinking to change soil ph in a large area.


The classic old method: manure, especially on your case, where you have a nearly neutral soil. But in general fertilizers acidify the soil, so often this is enough for vegetable garden (one fertilize near seedling). Not doing lawn scarifier helps (also this remove acidity, which is bad for lawn in a acid soil, but not so bad on normal soils). On flower garden: some plants/tree help to acidify soil, so with a good placement of element, you can have a acid corner. Peat-like substances are (should be) also acidifier.

Normally plants usually tolerate acid soil (but not extreme), but only plants evolved to tolerate Calcium can live in a non-acid soil: roots absorb nutrients, but if there is much calcium, acid plants absorb calcium and not the other needed substances.

About your product: "Sulphur" usually (and unfortunately) is just a nametag. Also that should be a sulphur salt/component.

The possible problem: the soil is huge, so nutrients moves, and basic soil will neutralize your acidifier, but the real problem is the watering. Usually water is also not neutral if your soil is not neutral. So you need to acidify periodically. Microorganism could not like many changes on acidity, so soil could become poorer. But this is often a problem on the inverse step: there is already acid parts on soil (see decomposition of leaves), so also acidophile organism. Soil pollution is also a problem, because acidifier could go into groundwater. But this is usually a problem with huge fields (and fertilizing at the same instant such large area).

So: check acidity of your water, and the structure of your soil. If water is not so basic, it is ok, else consider to collect rain water (before soil will increase the pH). If soil is light and sandy, your acidification will fail, and basic ions will enter so easily (so you need a waterproof "wall" inside the soil). On the other cases (more common): if you are building new gardening (in deep), you can uses several (and slow) acidifier on the base of soil. In any case, try with more natural methods and limited near root of the vegetables you need to acidify. Sulphur is not so bad (it is a common natural element), just it could wash away and cause some problem on other places, and drastic pH changes kill the soil, but nature will recover quickly.


As noted , you need a large amount of material to change soil pH. I have used calcium sulfate aka, gypsum / dry wall. I could get broken wall dry wall for free in pick-up truck quantities ( for a 1500 sq ft garden) . There is a little nuisance with the paper surfaces. It is not as satisfying as the pouring conc. sulfuric on the garden , but that is not for everyone.

  • I didn't know you could use dry wall. But how much does it take to lower pH? It would be great if you could update your answer with a graph. Thanks :)
    – Ljk2000
    Mar 18, 2018 at 20:46
  • I put roughly one pound per sq ft for each of 2 years. I did not measure the pH but vegetables grew fine. Mar 20, 2018 at 3:14

Applying elemental sulfur, or brimstone, to acidify alkaline soil with a high lime content is not cost effective. Bacteria act on the sulfur to turn it into sulfuric acid which acidifies the soil temporarily but then the carbonates present in the soil will return the pH back to what it was before.

acidification using sulfur

You are better off to apply composted manure and other organic materials. The humic acid present in the compost will free up phosphorus to the plants. You need to maintain a high level of organic material in the ground.


  • Thanks for this bit of information, it is nice to have learned of this now, but looking at the graph it looks like it takes a while for this to happen
    – Ljk2000
    Mar 19, 2018 at 12:55

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