Coniferous needles are no more acidic than other leaves. pH A pH between 5.5 and 8.5 is optimal for compost microorganisms. As bacteria and fungi digest organic matter, they release organic acids. In the early stages of composting, these acids often accumulate. The resulting drop in pH encourages the growth of fungi and the breakdown of lignin and cellulose. Usually the organic acids become further broken down during the composting process. If the system becomes anaerobic, however, acid accumulation can lower the pH to 4.5, severely limiting microbial activity. In such cases, aeration usually is sufficient to return the compost pH to acceptable ranges. Here is a link that might be useful: Compost Chemistry

no... you have two solutions for MATURE pines ... one.. get rid of them .. and solve the needle issue ... two ... remove the rock.. AND LEAVE THE NEEDLES UNDER THE TREES.. where they have naturally accumulated for millions of years ... let me ask you ... why are you forcing a preconceived notion of landscape rock under a pine tree ... pines are conifers .... ALL conifers shed their needles.. generally within 1 to 3 years ... increased by a good drought some years .. the thought that the situation .. on a 40 foot tree.. is going to get better.. or lessened in the future is problematic ... landscape fabric is a snakeoil salesman's joke on the gardening world.. a useless waste of money better spent ... as most weed seed is airborne .. so minutes after putting it down.. you have already been defeated ... roll this around.. if you left the pine needles to build naturally ... they would become a mulch.. a highly acidic mulch ... and reduce your weed problem exponentially ... you are actually defeating the trees attempt to suffocate weed production.. by removing the needles ... bob.. WAG here ... you are trapped in suburbia ... on a small lot.. with sidewalks and neighbors way to close.. and you are getting frustrated with a pine tree.. that in all reality.. is now becoming the FOREST MONSTER it is meant to be.. if there is any budget.. think long and hard about removal .. you are not going to change its inherent properties.. of growing and shedding needles ... in ITS lifetime ... otherwise.. its all good exercise ... good luck ken ps: you are stuck in a box .. i am trying make you look outside the box you have created .... Here is a link that might be useful: check out some of these pix.. you are fighting mother nature.. she ALWAYS wins ....

Well I want to use it as a mulch over the top of the composted leaf and manure mulch I usually use. Just a way to keep from splashing anything on the graft unions when I water. I also want to use it as a soil amendment for the blueberries I will be planting in a few weeks. Others would say watering more than 1'-2' away from the base of the tree would prevent this problem but with containerized trees it would also mean there would be no water in the pots.lol

I have been composting 95% + pine needles for about half a year now and there are a few tricks to make them decompose very fast. The first step is to shred the needles VERY fine. The mulched needle should contain only very short pieces of needles and a flour like consistency. Note:By breaking it down fine you can fit 3-4 times dry mass as appose to un-mulched needles. It also drastically reduces decompostion time too. The next step is to make the compost pile. Start by layering 2-3inches of pine needle mulch. Then pour 3-4 cups of chicken manure or what ever is the cheapest organic nitrogen source at your disposal. Wet down and mix that layer thoroughly.(Should feel like a wet sponge) Repeat til pile is built. Temp 150+ Turn in more nitrogen when pile starts to drop in temperature and wet when needed.(40-50Lbs of chicken manure)I dont add all my nitrogen a first because I dont want the pile to lose nitrogen by off gasing ammonia. Decomposition time can be further sped up by running it over again with a lawnmower toward the end of the compost cycle Total time is about 4-6 weeks from start to finish. pH of finished product is not known, but I will be following up on this thread with pictures and more info.