Earthworms play an important role in the overall health of the topsoil. Lumbricus terrestris is the scientific name for earthworms. While these subterrestrial creatures may seem slimy and crawly, they perform an important role in gardening by enhancing the health and porosity of the soil. Their presence can help encourage optimal growth in plants.
Most plants require medium- to fine-textured soil composition for healthy root growth. Heavy soils, such as those with a high concentration of clay, tend to smother the roots and limit the amount of water and air below the soil. Heavy compaction can also stunt the roots, restricting their ability to grow. Earthworms perform the task of aerating the soil. Their constant tunneling creates a network of corridors that loosens the soil and helps it absorb moisture. Loose soil allows maturing roots to grow without impediment.
Earthworms add nutrients to the soil in a couple of ways. They feed on decomposing vegetative materials in the soil, helping to release the trapped nutrients in leaves, bark, stems and roots. Their tunneling habits help to incorporate the vegetative materials below the surface of the soil. The worms also increase the level of nutrients with their castings, which is the digested matter they leave behind. Castings contain plant matter and digestive microbes that help feed plants, making them grow better. An increase in nitrogen helps provide strong stem and root growth and helps develop green foliage.
Not all types of worms are beneficial for plants. In fact, some can damage plants and restrict their growth. Pest worms can affect the exposed portions of plants as well as the underground roots. Cutworms, ear worms, hornworms, wireworms and fruit worms feed on the stems, leaves and roots of plants rather than the decaying matter in the soil. Depending on the extent of infestation, these worms can damage the fruits and kill the plants.
Pesticides, especially soil drenches, can kill the beneficial earthworms as well as the harmful worms. Removing the pest worms by hand can minimize damage to the plants and the earthworms. In situations where soil drenches are necessary, introduce earthworms a few weeks after the final soil treatment to help enhance the soil and the growth of the plants.