The most aggressive way to lower soil pH is to apply pure sulfur or flowers of sulfur. You should follow your soil test's recommendations, but in general, if you are applying sulfur to an area that does not currently have any plants growing in it, such as a new garden bed, you can apply it at a higher rate than in areas with growing plants. You can also add organic matter, such as compost or composted manure, to your soil annually and mulch with acidic organic mulches, such as pine needles. Adding organic matter slowly lowers your pH over time, while increasing microbial life and improving the structure of your soil.
Regardless of how, or if, you decide to amend your soil, Davis recommends growing plants that do well in alkaline soils, such as linden trees (Tilia spp.). "Gardeners who have their heart set on growing an acid-loving plant like a blueberry should grow it an container," Davis says. "That way, you only have to change the pH of a small amount of soil."
Jessica Davis is coordinating a new, interdisciplinary program devoted to organic agriculture at Colorado State University.