Demystifying Soil pH

The pH (and you can find various arguments about exactly what pH stands for) is the measure of your soil’s acidity, and it’s often a huge area of debate among gardeners. I try to keep this discussion simple so I don’t make your head spin, especially if you have little or no acquaintance with chemistry. Too low of a soil pH means the soil’s too acidic, and too high of a pH means the soil is alkaline. Generally speaking, you want your soil pH to be on the slightly acidic side for the vast majority of garden plants. Extremes are rarely good.

The pH scale ranges from acidic to alkaline — 0 to 14, with 7.0 as neutral. The really good news is that many soils are fairly close to neutral. Acidic or alkaline soil isn’t bad soil or bad for plant growth per se. But the minerals in the soil that are important to plant growth and health have a tough time getting to the plants when the pH isn’t right for the particular plant. Scientists have discovered that beneficial soil bacteria don’t function well unless the soil pH is relatively close to neutral. These bacteria are important because they break down organic matter and make sure nutrients are in forms that plants can use.

Of course, some plants prefer or are well-adapted to pH levels that are a little more acidic or a little more alkaline. And some soils are naturally so; when in doubt, you can take your cue from the native plants. Examples of plants that like acidic soil include blueberries, azaleas, rhododendrons, most other broadleaf evergreens, and heather. So in the New England states, where many soils are acidic, you see native blueberry plants. And if gardeners in that region want to grow blueberry bushes (albeit improved, bigger-sized fruit varieties), they should have good luck.

Examples of plants that like alkaline soil include penstemon, dianthus, baby’s breath, and beets. So in the Southwest, where many soils are more alkaline, you see native penstemons. And if gardeners in that region want to grow these flowers (native species or improved selections), they should have good luck.