An earlier post discussed the importance of soil testing, which tells you, among other things, about the pH value of your soil. The more rain your soil gets, the more likely it is to be acid. Dryer climates (such as the Western U.S.) have more alkaline soil, while here in New England, we generally have more acidic soil. Most plants (including veggies) grow better in slightly acidic soil. On a scale of 1 to 14, with being the most acidic and 14 being most alkaline, the optimum pH level is between 6.5 – 7.0.
But why does soil pH matter to plants? Because extremes in pH (whether acid or alkaline) can create toxic levels of certain minerals, and can also cause beneficial minerals to be less available to plants.
To amend acidic soil (increase the pH), add material containing lime, such as agricultural limestone, dolomitic limestone, or even wood ash. But as always, don’t overdo it–extreme swings in soil pH cause stress to friendly organisms and bacterial that live in your soil.
Amending overly alkaline soil (decrease the pH) is more complicated. The best thing you could do is add lot of organic matter / compost. What you end up with is humus, which creates humic acid. You can add artifically produced acidifiers to your soil–but you probably don’t want your kids running around in ammonium sulfate or other such garbage. A better idea might be to select garden plants that like alkaline soil.
Try to get professional recommendations on soil amendments–it’s my understanding that UMass provides recommendations with your soil test results.