Q.Is A Black Walnut Tree (stump, Roots) Toxic To Garlic?
Have planted garlic adjacent to a black walnut stump for several years. It has always come in perfectly. This year nothing. We did have an open December (NO SNOW COVER) and then some severe cold. Was it the walnut leaching into the soil or lack of mulch protecting my garlic?

Certified GKH Gardening Expert
Garlic is supposed to be tolerant of juglone in black walnut trees, so it must be something else. Perhaps the severe cold without protection did the garlic in. These articles should help:
https://www.canr.msu.edu/news/growing_vegetable_gardens_near_black_walnut_trees
https://www.gardeningknowhow.com/edible/herbs/garlic/growing-garlic.htm
Your particular type of garlic may be here: