Lower the pH of my garden soil
Question: I had my raised-bed garden soil tested last year, and the pH was around 7. Most of the plants I want to grow (tomatoes, lettuce, cucumbers, broccoli) like the soil a little acidic, so I was wondering what's the best way to reduce the soil pH. I suspect that the neutral pH affected the flavor of my tomatoes, as the ones I grew in pots tasted quite a bit better than those in the garden beds. Of course, that's anecdotal evidence, but...
I've heard of adding sulfur to the soil to acidify--are there any ill effects of doing so? I've also heard of adding coffee grounds, but I don't drink coffee. (I've also also heard that pine needles--which are abundant here--are acidic; if I used them as a mulch, would that effectively lower the pH, or is that not a good idea?)