Make Soil Microbes Your Friends

By Marsha Goldberg, Fairfax Master Gardener
carrots in soilMost gardeners know the aphorism, “Take care of your soil and the soil will take care of the plants.” By providing needed nutrients, healthy soil results in plants that are more likely to thrive and fight off disease and pests without the use of chemical fertilizers, insecticides and fungicides. But what exactly is a healthy soil, and how can the home gardener achieve it?

In the past, scientists and gardeners thought of soil in terms of the presence or absence of macronutrients — nitrogen, phosphorus and potassium — as well as micronutrients such as magnesium and iron. Correcting the balance of the soil involved adding fertilizers and other chemicals, whether organic or synthetic. Now, however, soil scientists are turning their attention to the living matter, especially the microbes, that live in the soil – microbes that include bacteria, fungi, nematodes, protozoa, and earthworms. Ninety percent of soil functions are due to the activity of microbes. These microbes affect the texture of the soil but also have an impact on its chemical balance. Their activity creates tunnels and pores that help the soil absorb and retain water as well as hold oxygen, making it available to plants. Just as important, microbes have a symbiotic relationship with plants, especially the roots. Microbes eat and digest waste products emitted by plants. The microbes, in turn, produce their own waste, which contains nitrogen compounds. Plants take this up when the microbes digest, die and eventually decompose.