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Marin IJ Articles

How to care for those tiny, often forgotten, creatures in your soil

  • Marty Nelson
  • Is your garden habitat-friendly? The goal of a habitat-friendly garden is to provide a natural environment that attracts and sustains desirable living creatures.

    We often measure our success based on the number of bees, birds and butterflies we observe in our garden. However, your garden could not welcome wildlife without the help of creatures we can’t see, those hardworking organisms that live beneath the soil surface. The soil is teaming with life in much greater numbers and diversity than what is visible above ground, yet it is a habitat we often overlook.

    The main groups of soil inhabitants are bacteria, protozoa, fungi, nematodes, arthropods and earthworms. Each group has a particular role to perform in the overall task of cycling nutrients through the environment. In healthy soil they form a dynamic community and engage in a microscopic “circle of life,” which ultimately produces materials for plant growth, improves soil structure, and degrades pollutants. There are some bad actors in these groups and they can cause plant damage, but in healthy soil the good guys are much more numerous and maintain a positive balance.

    The smallest members of the soil community are the single-celled bacteria. They work as decomposers to break down organic matter. Some bacteria help in the conversion of nitrogen into compounds that plants can absorb through their roots. The larger single-celled protozoa feed on the bacteria, controlling their population and helping with the release of nitrogen. Like bacteria, fungi decompose organic and inorganic materials in the soil and can form beneficial associations (mycorrhizae) with plant roots to aid absorption of not only nitrogen, but also other nutrients and water. Evidence of fungi can be seen as the white hair-like threads (hyphae) on the underside of leaf litter. Mushrooms are the spore-containing fruiting bodies of fungi.

    Fungi and bacteria are eaten by nematodes, tiny non-segmented roundworms that likewise aid in the release of nitrogen and other nutrients. Nematodes also prey on each other and the beneficial ones help to control the pests.

    Soil-dwelling arthropods range from microscopic to several inches in size. This group includes springtails, sow bugs, mites, and millipedes. Arthropods can feed on fungi and bacteria, shred dead plant material, and eat other arthropods, thus doing their part to transfer energy through the soil and into plants.

    Finally, there are the earthworms, considered to be the generalists because they consume many of the smaller soil organisms. They enhance soil by burrowing into it and excreting nutrient packed wastes (castings) that contribute to plant growth when decomposed by bacteria and fungi (remember that “circle of life”).

    You can create a friendly habitat for a vast community of soil dwelling wildlife by providing them with the basic necessities — food, water and shelter. Organic matter, supplied by composting and mulching, is the food that keeps the organisms alive and improves soil structure. Moisture is essential to all the vital life processes constantly occurring in the soil and the more improved the soil structure, the better the soil is able to retain water regularly delivered by rain and irrigation. Shelter means protection from soil exposure, disruption and injury. Tilling the soil disturbs the network formed by the soil inhabitants and disrupts their communal work. It’s best to minimize soil cultivation when it can be avoided.

    When soil becomes compacted by foot traffic or construction, the spaces that hold the air and water needed by the underground organisms collapse. Overuse of quick-release fertilizers and the application of insecticides and herbicides can also injure the little creatures you want in your garden. More information about preserving this vital living ecosystem can be found by following the link to “soil health” on the Natural Resources Conservation Service website at nrcs.usda.gov.

    As you enjoy your friendly habitat garden, remember the billions of soil microbes under your feet. Your attention to their needs can increase the complexity of their community and improve their ability to do their important jobs.