@toxcrusadr Assuming I stick with elemental sulfur, how often should I be re-applying? I guess technically I should be redoing a soil test each time before re-applying, to see how close to the target I am?

I've heard it can take 3-6 months to work, so rather than applying it once during the season you could do spring summer and fall or something like that. Smaller applications each time of course. I'm just spitballing.

If you are going to test frequently I'd consider a home test, but get a good set of test strips and avoid the cheapie kits.

@toxcrusadr I have a digital pH meter that I use for sensitive measurement of dairy ferments. They claim the same probe can be used for soil measurement, but up to now, I had been trying to avoid contamination of the probe. I will work through those issues and probably start using my probe for soil.

Just something I wonder about.

In California, the number of users on well water or untreated surface water is going to be rather small. So I assume most California posters here at GW/Houzz will be watering with municipal tap water, and that in a low rainfall climate, most of their plants water will come from that. Tap water is usually treated with something like Sodium hydroxide to raise the pH. Isn't it going to be a constant battle to keep the soil acidic?

Not trying to be a doomsayer, just wondering. Many years ago there was a wonderfully acerbic garden writer in the Bay Area, he unfortunately died at a relatively young age. I remember him saying that various plants were failing in his garden due to "insufficient hydrogen ions!"

@UpperBayGardener (zone 7) Our tap water is around pH 7.7, so only slightly basic. Correct me if I am wrong, but the plant is not drinking water like an animal would out of the tap. Water permeates the soil, and then it quickly has its pH altered by soil ingredients. If you do not believe me, put some peat moss in a dish and then add tap water with a pH of 8. Wait 30 minutes. pH will measure around 4.5. The plant did not drink most of that alkaline water during the 30-minute exposure at higher pH. The plant is absorbing water slowly over the next three to four days, therefore the plant gets the benefit of the rapid pH shift. I m sure someone like @tapla (mid-Michigan, USDA z5b-6a) could give better insight.

I'd say that's most likely true, but keep in mind that adding different pHs together essentially causes a little bit of cancellation every time. How long it takes to actually change the pH of a soil from its natural number is highly dependent upon the exact composition of soil and the water. In any case in a dry climate there is less rainfall (unmineralized water) to flush things out and let them return to the natural state.

This is purely from a chemist's perspective. I don't actually know whether it's an issue in practice. It's encouraging that the water is pH 7.7. In some places it's as high as 9, which is like 1500 times more basic.

Oh, as for the pH meter, you'll be testing water solutions rather than soil itself - 50/50 distilled water/soil, shake and settle a few minutes, then test the water. After a good rinse you can soak the probe in alcohol, shouldn't hurt it and will kill anything eventually.

@toxcrusadr I will show by some examples why the dosing of sulfur for a container is a frustrating problem.

EB Stone's elemental sulfur product says on the box to apply around 0.007 pounds per square foot. In conversation with EB Stone's internal soil expert, he suggested going from 6.5 to 5.5 is easier than their instructions, so I should use 0.073 pounds per square foot. But that number is 10 times higher than their box instructions for the more difficult conversion. :)

The website you referred me to gives 0,0213 pounds per square foot.

The Espoma elemental sulfur product suggests using 0.12 pounds per square foot.

So four different contexts give me ranges of 0.007 to 0.12 pounds per square foot. That's a difference of a factor of 17, for the same application.

But then to make it even more fun, NONE of these sources give you a volumetric estimate. It's all surface applications for in-ground plantings. As container gardeners, we want to deal with volumes of soil, so cubic feet, not square feet. And none of these estimates suggest a conversion to cubic feet.

So if someone here is mixing up 25 gallons (~= 3.34 cubic feet) of potting soil with a pH of 6.5 and wants to lower that to 5.5, I calculate about one cup of elemental sulfur would do that work. Does that sound even close to anyone who has done this before? One cup seems like a lot of sulfur for 3.3 cubic feet of soil, to me.

Looking at this in terms of a percentage, one cup ~= 0.0625 gallons, so the elemental sulfur would be added as about 1/4 of 1% - or 0.25% - to to any given volume of container soil. Does 0.25% of the container as elemental sulfur sound reasonable?

I don't think 1 cup in a cubic yard sounds all that high. It's not instantly changing the pH (stating the obvious here), it happens over time, and it's constantly either being washed out plus the soil is trying to return to its base (natural) pH, so it's consuming that acid as it's produced.

You can always adjust it with lime if it overshoots.

Edit:

Here's one about pH when growing in pots: https://rootmaker.com/sites/default/files/pdf/pHFactorContainersE.pdf

And here's one about pH when growing in the ground: pHFactorFieldSoils.indd (rootmaker.com)

To find the source site search "lacebark inc.". The now elderly author is an "inc." operating his own research farm these days but was previously a university professor. And decorative plant production methods innovator who for instance had discovered by 1969 that amending of individual planting hole backfill for woody plants with soil texture altering materials such as bark, peat and sand does not improve plant response.