A perpetual question Master Gardeners hear is “How do I kill the worms in my lawn?” Before I share the answer we give, let’s talk about worms.

The majority of the worms we find in our yards are the red wigglers who eat decaying vegetable matter and night crawlers who live in the soil and carry organic material into the soil. It is the night crawlers that make the lawn lumps!

Thousands and thousands — perhaps as many as 50,000 worms — live in your yard if your soil has a source of organic material for the worms to eat. Earthworms turn dirt into soil.

Each night the worms deposit worm castings — their droppings — by the surface opening and take down more leaves and organic material to digest during the day where they also leave castings. It appears that worms do not sleep. These castings release the nutrients that were stored in the leaves so that plants can reabsorb them.

Their burrows, which are the size of the diameter of a pencil, spread down about 8-10 feet into the earth. These burrows not only are the homes for the worms, but the cavity contains organic material brought down from the surface. These long tunnels provide air and water tracks for plant roots, and that is very important for your garden.

The night crawler’s lifestyle helps to create what is known as soil structure. This is the network of insects, microorganisms, various-sized rock particles, air and water passages. The strength of the soil structure helps create a healthy environment for all plants. Tilling the garden breaks up the soil’s structure, and this is one of the reasons that this annual regimen has lost favor with knowledgeable gardeners.

If your garden soil is fertile and has enough organic material incorporated into it, you can preserve the worms’ work by merely weeding the garden plot in the spring — and then digging small trenches for seeds or individual holes for plants.

The most amazing fact about night crawlers and red wigglers is they are not native to America but were introduced from Europe beginning with the first settlers on the East Coast. According to Amy Stewart in “The Earth Moved: On The Remarkable Achievements of Earthworms,” ballast material from England was dumped at Jamestown and other sites when the ships were filled with barrels of tobacco and other American products. That ballast was rocks and soil. The worms and their egg cocoons were still alive and ready to take on American dirt.

The last ice age had killed off most of the worms on the East Coast, so the soil was not very fertile since it did not have worms to incorporate organic material in it.

The earthworm, that “pesky” night crawler, changed the dirt all across the U.S. in about 200 years because settlers carried plants with them as they migrated from Europe and all across the American continent. The worms increased the water-holding capacity of the soil, increased the nutrients and introduced micro-organisms that plants require.

Charles Darwin’s last book, “The Formation of Vegetable Mould, Through the Action of Worms with Observations on Their Habitat,” published in 1881, was the compilation of 40 years of observation of worms on a section of untilled land on his estate. This book made people aware of how worms process leaf litter. If we did not have worms, dead leaves to the height of many feet would cover the world was one of his conclusions, and the soil would be far less fertile.

So what is the advice about killing worms? Have you ever noticed after a heavy rain that worms come out onto the driveway? This is because the burrows have filled with water and forced out the air the worms need. The same thing happens when a homeowner over-waters the lawn. The worms are pushed to the surface. Another reason that the lawn mounds appear is that the lawn is not watered consistently or enough, and the ground is damp only a few inches deep. Consequently, the worms stay at the surface of the soil.

So the answer is — if you kill the worms, you will kill the soil’s fertility. Proper lawn irrigation will keep the worms happy, deep in the soil, and all will be well!

A WSU Master Gardeners of Chelan County column appears regularly in the At Home section. Bonnie Orr is one of five columnists featured.