let me rephrase that. I tried the soil acidifier from Epsoma, but I was a big ol wuss and I know that I didn't put nearly enough.

UCG's - used coffee grounds - are nearly neutral in pH and will not change soil pH. Virtually all the acidity is extracted with the coffee itself. If you want organic or natural soil acidifiers, try cottonseed meal, peat moss or agricultural sulfur. And if you retry the Espoma product, apply according to label directions :-)

None of these are immediate fixes.....it takes time for soil acidifiers to work.

I can suggest not adding any used coffee grounds unless you put them in a compost pile or bin and fully compost them first. You may see some plant death with smaller plants if you add them straight on. It would be better to buy a bagged soil compost type product if you want a quick fix without composting. UCG are also used as a weed killer when applied directly to the weeds.

tropical, do you have any cites or references that support this notion? I've done a lot of research on UCG's and I've never encountered anything that indicated they had any allelopathic or herbicidal characteristics. They are generally considered a low nutrient fertilizer (NPK 3-1-2), in much the same way most other seed meals are. They can be hydrophobic if allowed to dry or crust over, but I've never heard them responsible for plant death.

I added plenty of coffee grounds around the base of two Nikko blue hydrangeas and encountered no problems. They were a lovely blue, but I can't say they wouldn't have been the same color without the coffee grounds.

Anyway, now the grounds go in compost but I certainly didn't harm the hydrangeas with direct application.