Mowing over black walnuts in yard?
Thank you for allowing us to assist you in some way. Plants do not grow well under Black Walnut trees as you attest to you grass condition as the tree releases juglone which is toxic to plants. Grasses will grow under these trees but not exceptionally well. If you mow over the walnut nuts it will allow the juglone to release more readily but the grass will usually survive but not exceptionally well. If your mower is set low below 3” the blades will hit the nuts and possibly damage the blades as walnut shells are used as a blasting abrasive. It would be best to set your mower height to 3” and leave the nuts for the squirrels. I have listed below your County Extension Service which may offer additional advice. Again thank you for your question.
Butler County OSU Extension Office
1802 Princeton Road
Hamilton, OH 45011