Not sure if this has been discussed before.
Walnut trees (and related trees butternut, hickory,....) produce a compound that is toxic to other plants and some animals, jugalone.
You should be aware of this if you have them growing near where you garden or plan on planting other things. Also if using the leaves as mulch.
I think this explain the loss of one of my apple trees.
The links have lists of tolerant and intolerant plants.
https://extension.psu.edu/landscapin...oducing-plants
https://gardenerspath.com/plants/lan...lone-toxicity/
https://www.ontario.ca/page/walnut-toxicity