I'm not sure if any of this may help a short term problem or a quick fix but the coffee trick sounds easy enough to try out.
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.
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”.
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:
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.
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”.
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.
