Dawn - I wouldn't go the vinegar route - a little too imprecise. I would recommend a couple of things. You can use a fertilizer for acid-loving plants. Espoma makes a good one. I wouldn't fertilize it at this point as any new growth might not have a chance to harden off. We're really only about 2 months away from our first frost. But for sure use some in the spring. One thing that you can do now is pull back the wood mulch and mulch with 1" to 2" of milled sphagnum peat moss. It's the stuff that comes in different sized bales. Don't put the wood mulch back on top of the peat moss. The peat moss will help acidify the soil gently.
