pH Level for Bacterial Growth in Soil

pH in Soil

• pH levels in the soil range from about 3.4 to 8 and usually lean more toward the acidic side of things. Many factors, imposed both by nature and humans, can affect the pH of the soil, including temperature, the addition of pine needles or limestone, and yes, even the bacteria and fungi that live in the soil beneath. How bacteria are affected by pH levels can be a hard thing to pin down for scientists, as oftentimes bacteria affect the pH just as much as pH affects them.

Varieties of Bacteria

• A handful of even relatively healthy soil will contain billions of bacteria in it and hundreds of species. The conditions in which these bacteria thrive are as numerous as the varieties of bacteria that live in the soil. Beyond the life of soil are extreme bacteria known as acidophiles and alkaphiles, which live in extremely acidic or alkaline conditions. These are not generally found in soil populations but everything else in between is. pH does not directly affect overall bacteria growth in the soil, however, it does affect the growth of one of the most effective bacteria for most gardener's needs: actinomycetes.

Actinomycetes

• Actinomycetes are the bacteria that do much of the legwork in breaking down organic matter in soil and freeing up nitrogen into the soil, making it available to plants. These beneficial bacteria are the backbone of any healthy compost pile and a healthy soil thereafter. Actinomycetes thrive at relatively high pH levels, from 6.5 to 8. A standard healthy garden soil will have a pH of 6.5, so actinomycetes prefer a pH that is higher than that of many soils, but you can still have a healthy actinomycetes population if your soil has a pH of 6.5.

pH Adjustment

• In most places around the country and depending on what kind of plants are being grown, if soil needs adjusting, it usually is too acidic and needs a higher pH. A typical method for doing this is adding limestone to the soil. However, if you are trying to optimize bacterial growth and change your pH, compost is the best answer. By adding compost to the soil, the soil is inoculated with the beneficial bacteria that are desirable for any good garden, and the pH is adjusted at the same time, helping to create an environment that the newly introduced bacteria will stay and grow in.