This is the same confusion that comes up over the use of coffee grounds. Both the needles and the grounds are acidic but once you apply them to the ground the PH of them will come up to almost neutral in time. It still though is adding organics and tilth to the soil and the plants will love it BUT you can't use those items as the sole acidifier in soil that has an unsuitable PH. But using the grounds and needles as a mulch on top of acidic soil is great. In PA on the farm we grew in just about pure pine needles and the resulting soil the needles created. We added sulfur to the plants yearly and they were huge gorgeous bushes and never once did we test the PH.

Sounds like free mulch to me! Thats the best kind. You could always take a bag of it and compost it to see what you get for ph when it breaks down? If anything it would be a good soil amendment.

I once tested the soil under some huge white pine trees where the needles had been allowed to rot for decades. It had the same slightly acidic pH as the soil in the field well beyond the range of the needles.

I've never read a credible source claiming they are acidifying but have often read their affect is neutral.

It's a great mulch for blueberries though. You can spread them thick and they almost completely stop weeds. You don't have to worry much about spreading them right up to the plant because they repel water and won't cause wood to rot.

Yes,there are long and short needle Pine where I work and when the leaves turn brown,fall to the ground and accumulate enough,I rake, collect and put them around my plants.Not much grass grows through.Brady

Marvelous mulch - use 'em as such. I wouldn't squander them or waste the time and effort entailed in 'composting' them.
Like hman, I've never seen evidence that they lower soil pH, but rather, that pines tend to prefer an acidic soil, so soil pH underlying a natural blanket of pine needles is usually acidic.

Well, I don't know about pine needles, but I can vouch for the acidifying effect of oak leaves. I have been putting them on everything for the past few years. My soil here is naturally close to neutral, in the upper 6's. My 'Nikko Blue' hydrangeas which always bloomed pink have just in the past season turned back to the blue they can be in acidic soil. Soil pH needs to be below about 5.6 in order to allow aluminum to be soluble and available to the hydrangea. Gotta be the oak leaves, can't think of any other reason they would turn blue after close to 2 decades of blooming pink.

Den, I believe that is no proof of an overall change in the pH, only the availability of iron. The acids released during the decomposition process free up the iron near the soils surface where the feeder roots pick it up. I've often seen this same result for blueberries where they've thrived under a mulch even though the pH is much too high to provide the necessary iron otherwise.

I'm glad you brought it up because I didn't remember this when discussing the advantage of using a pine needle mulch. The info is still up there but access is getting slower.

The coffee grounds & the pine straw become neutral when they are composted(rot).
The coffee grounds will change the pH a little, more so if you make a UCG tea for the plants.
I know I have a few tons of Used Coffee Grounds/chaff.
Remember your mother's Hydrangea turning from pink to blue based on the coffee & tea grounds.

Here is a link that might be useful: Coffee chaff

dont miss the great FREE mulch ...

but i remember it this way ...

pH is an exponential function ... the tonnage of material you would need.. to change the pH by 1/10 ... would probably cover your garden in hundreds of feet .. for hundreds of years ... as harvestman suggests ...

if you want to change pH ... do it the right way ... otherwise.. these type of claims are basically based on the 'hope and prayer' system of soil management ...

ken

Actually, Den's post made me realize(remember, acutally) that you don't need to permanently change the pH of the over all soil to maintain healthy blueberries. I have on several occasions found thriving BB's in soil almost neutral where the plants were annually mulched. Others have posted here of similar experience- even in soils with the pH in the 7's.

Carl Whitcomb did experiments sometime ago that showed that acid loving pin oaks lost their chlorosis within a couple of months of a surface application of sulfur even though the only part of the soil with a pH out of the high 7's was the soil surface and the pH change could not be measured. Acids released by composting mulch seem to do the same thing.