Question
I live in a cool climate (3200 ft ele, zip-96057)
my lawn is under large pine trees, partial shade. The lawn gets very bumpy, almost like it wants to buckle. The grass is mostly ryegrass/red fescue. I am thinking that a aereator would help but am not sure. the soil here is volcanic, very rich black dirt. Any suggestions on what makes the lawn get so bumpy?  thanks

Answer
tree roots can compact the soil making it settle and bumpy. Same can happen if above average amount of organic matter (partially decomposed wooden material) which settles unevenly as it decomposes in the soil. Finally, in some cases earthworm activity can create mounds of dirt and compact the soil.

Aerating the soil annually, or even using a dethatcher set at lowest setting will help.

Otherwise, mow the lawn tall (2.5-3.5") and recycle clippings to the lawn. This will help keep a soft balanced feel and any uneven surface will be less noticable.