I happen to like Black Walnut trees. The nuts can be messy, but squirrels love them and will remove them from your lawn. I grew up on a farm with a grove that had several rows of giant walnut trees. Stories of my youth aside, walnut trees and gardens don’t go together. Don’t plant a garden near these trees (see my garden under my tree) and if this is already your situation do not use the leaves as a compost for next year. I like to rake the leaves. Pile them on top of my raised beds. Cover the leaves with some dead branches and then dig what remains of the leaves into the soil in the Spring. Not a good idea if you plan to grow certain plants in these beds (e.g., tomatoes).
According to Iowa State University (my school), walnut trees produce juglone – a substance secreted by the roots and present in the leaves that can cause severe damage and even kill solanaceous crops (tomatoes, potatoes, peppers and eggplant). I have no idea what a solanaceous crop is, but juglone is going to be my new vocabulary word for today. Say it with me – juglone.
Whoops – always read articles to the end. Walnut leaves can be composted because the juglone toxin breaks down when exposed to air, water, and bacteria. Now I am going to have to rake and pile.