Sulfur is probably your best choice. It works slowly but will lower your pH. Ferrous sulfate and/or aluminum sulfate also work well, and very quickly. Vinegar, citrus juices and peels, etc., and other sources of organic acids are not good soil acidifiers except in the very short-term (days). As they biodegrade, their effect is lost.

What you've done may be ok. You'd get a more uniform result by spreading the sulfur over the entire area under the drip line (and out a foot or two beyond it) and raking it in, or dissolving the FeSO4 or Al2(SO4)3 in water and sprinkling it over that entire same area.

I do wonder why your pH remains that high -- are there chunks of old construction concrete in your soil, or is your soil fill dirt containing a lot of shell? Or are you in an area where the limestone bedrock is near the surface? Or has the tree been heavily limed in the past? Most Florida soils are naturally quite acidic until or unless you bring the pH up.

Actually the pH is over 7 in some areas around the dripline. I spent an hour searching pH on the Citrus forum here and there was a thread Bencelest said ideal pH for him was 5.4, and I think you yourself in that thread mentioned that typical Florida soil can be as high as pH 8.0 and not very fertile at all and it doesn;t affect fruit production very much. Nothing has been done as far as new soil filled with the exception of me adding compost and most of that is pH neutral. I know you advocate not to mulch or to add compost, but I know what works for me and plain Florida soil isn't it.

I also wanted advice on whether it is wise to use mineral acids like muriatic; hydrochloric or sulfuric for citrus to lower the pH more long term than the quick fix method of diluted iron sulfate.

Posted by malcolm_manners 9b C. Fla. (My Page) on Mon, Jul 16, 07 at 22:12

It's your soil pH that counts, and irrigation water can slowly change the soil pH, but it is likely to be a slow thing. Most irrigation water on commercial citrus in Florida, California, and Texas, is up in the 7.1 or higher range, often 8.0 or higher. Not a problem at all, as along as the soil pH is monitored and adjusted as necessary. The more clay and/or organic matter there is in your soil, the better buffered (able to resist rapid changes in pH) it will be.

MM there are some bits of shell in the sand, but not an overly amount. As far as concrete or limestone beds I have no idea but I have heard that limestone is prevelent deep in the ground making some well very alkaline even though the water is sulphur (quite an oxymoron, huh, alkaline sulphur water. Similar to acidic lime haha)

Notice that that was irrigation water that I said was often pH 8.0, not soil. The only places we have that high a soil pH would be where the bedrock comes to the surface, such as in Homestead, or Naples, or other southern coastal areas. And yes, most "sulphur water" in Florida is alkaline.

Mineral acids -- yes they'd work, but no, they are not recommended -- too nasty to work with, and with no advantage over the other stuff I've mentioned, at all. They cost more, they're harder to use, they're more likely to injure you and/or your tree, and they don't lower the pH any better or faster than the two sulfates you're using.