Earthworms and Your Lawn

Not long ago, a reader wrote to us about a problem he is having with worms and his lawn. More specifically, he thinks that the worms in his lawn are causing it be uneven and rough, and as a result he is wondering what kind of worms he is dealing with and how he can get rid of them. One’s lawn is a precious thing, so we understand his dilemma.

The first question – what type of worms are in our reader’s lawn? – has a simple answer: earthworms, or in any event this is likely the case, as earthworms and lawns go to together like deer and the forest. Anyone who has a lawn has probably seen plenty of earthworms, but we’ll provide some quick background anyway. Earthworms are a part of the subclass Oligochaeta, which belongs to the annelid phylum. There are around 10,000 species of terrestrial and marine worms in the Oligochaeta subclass, some of which are the various kinds of earthworms. Okay, enough taxonomy.

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How can earthworms make a lawn uneven? First, earthworms aerate soil, or at least the top two feet of it, by digging tunnels through it. As any gardener will tell you, this is a good thing because aerated soil is conducive to plant growth. So, worms in your lawn indicate that healthy soil is beneath it. However, tunnels dug by worms can collapse, and this might cause the surface of your lawn to become slightly uneven. This isn’t a major an issue, though.

The bigger problem is this: because worms consume organic matter as they tunnel around your lawn, they will inevitably leave behind worm castings (vermicast, worm humus, or worm manure, to list a few other names). Again, this is largely a good thing, as worm waste is nothing more than nutrient rich fertilizer. Worm castings become problematic in excessive amounts because as they accumulate over time, your lawn can become bumpy, which in turn can cause you to cut too many green shoots while mowing, a problem called “scalping.” Scalping can give rise to brown spots on your lawn and can also encourage weed growth. Apart from producing too many castings, an excessive number of worms on your lawn can also attract animals like moles (because moles eat worms), which can lead to additional yard troubles. (When moles dig around your yard, it can obviously be a problem.)

What can you do about the worms in your yard? It should be stated up front that you don’t want to remove worms from your lawn because they are so helpful in keeping your soil healthy. That said, you should avoid over-watering your yard because this will encourage worms to stay near the surface (worms love moisture), causing them to leave more castings on the surface and potentially attract additional pests like moles. Also, when worms castings are found, wait for them to dry and then rake them into your lawn. (Note: It will be fairly hard to “find” worm castings, as they basically just look soil. So, if you notice that worms are living in your yard, as they likely will be, you should rake periodically.) This will prevent the castings from building up. Following these two bits of advice should keep your lawn fairly level. However, if your lawn is already severely bumpy from years of worm-casting accumulation, some form of lawn restoration may be necessary.

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