I have never had experience with this, never had to do it. A search returned this piece: Perhaps someone who has personal experience can chime in
https://www.grow-it-organically.com/changing-soil-ph.html
Lowering Soil pH
Why would you want to lower soil pH?
If soil pH testing indicates your soil is greater than 7.0, you have an alkaline soil, and changing soil pH may be called for, depending on what you’re growing.
As soil acidity increases, minerals like phosphorous, iron, and zinc become more available.
In alkaline soils, these minerals—especially iron and zinc—are bound up and less available. Fruiting plants like tomatoes, peppers, squash, and melons need these minerals to flower and set fruit.
Soil acidification also makes life more difficult for many weeds. Weeds are early successional plants that evolved in thin, alkaline soils. In acidic soils, many weeds are weaker competitors.
Ways to Lower Soil pH (Make Soil Acidic)
Soil pH can be lowered by half a point—from 7.0 to 6.5, for example—by increasing soil nitrogen. Adding compost, manure, or organic soil amendments like alfalfa meal to the soil can help drop pH over time by increasing bacterial populations. Click
Here for a list of concentrated organic nitrogen fertilizers that can be used to lower soil pH by small amounts.
There's a myth that coffee grounds (2-0-0) are a quick fix for lowering soil pH. Most of the organic acids in coffee are water-soluble, and flush out into the brew. Coffee grounds have a pH around 6.8, close to neutral, so they won't do much to lower pH. They do add a little nitrogen, so they can help reduce pH over time, just like manure or compost.
If you need to drop soil pH more quickly, try watering your plants with leftover (cold) coffee, diluted 50-50 with water. This works especially well for houseplants and container vegetables.
To lower soil pH by larger amounts (more than half a point), use
Elemental Sulfur, sometimes called “Flowers of Sulfur”.
Order Elemental Sulfur
When using sulfur for changing soil pH, be aware that the acidifying effect depends on soil bacteria (
thiobacillius), which oxidize the sulfur and release dilute sulfuric acid into the soil
over a period of weeks to months.
Because the acidifying effect of sulfur depends on soil bacteria:
The sulfur must be dispersed through the soil to be in contact with these bacteria. Make sure you mix the sulfur thoroughly into the soil. Otherwise, there will be strongly acidic areas around blobs of sulfur, and no effect elsewhere in the soil.
Sulfur only works during the summer, when the soil is warm and bacterial activity is at its highest.
Sulfur is not a quick-fix for changing soil pH. After application there is a delay of several weeks to several months before soil bacteria break down the sulfur to acidify the soil.
Elemental sulfur is acceptable as an organic soil amendment for changing soil pH under National Organic Program (NOP) guidelines.
When using elemental sulphur for changing soil pH, it's best to divide the amount to be applied to achieve the desired drop into
2 or 3 applications over the entire season, instead of a single application. Applications should be 6-8 weeks apart.
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