Q. In the last 10 days we have experienced a major worm exodus out of our yard onto the sidewalk. I recently applied a lawn fertilizer with no pesticides in it. One of these die-offs was after a heavy watering and one was after no water for 2 days. Is this normal this time of year?
A. It is hard to pinpoint the reason why worms did a death march out of your lawn but the usual reasons are because they can't get enough air or some irritant is applied to the lawn.
A lack of air usually occurs because the soil is kept too wet, like right after a heavy rain, or is compacted from traffic or heavy equipment. This can be corrected by aerating the lawn once a year.
It is possible that a heavy application of fertilizer might irritate them enough so they would leave. Most fertilizers are salts. If the soil becomes salinized this could be enough of an irritant for earthworms to try an evacuation.
Quick release fertilizers (these are the most inexpensive types) easily dissolves in water so fertilizer salts are released into the earthworm environment very quickly. Next time apply a fertilizer that has half of its nitrogen in a “slow release” form. This releases the nitrogen more slowly, as well as the salt content, and is easier on your worms.
It is also a better fertilizer for your lawn. Slow release fertilizers encourages moderate growth and is applied less often. Quick release fertilizers tend to “jolt” the grass into rapid growth and then disappears quickly.