From a huge (English) Walnut tree, we have a huge pile of leaves which have been breaking down since last fall. Any advice on adding them to our compost pile would be appreciated.
My advice would be not to do it. Walnut leaves contain chemicals that suppress plant growth, so adding them to your compost would be counterproductive.
When plants are planted near or under walnut trees, they tend to yellow, wilt, and die. This decline occurs because walnut trees produce a chemical called juglone. Juglone is found in leaves, stems, fruit hulls, inner bark and roots of walnuts. English walnuts, hickories and pecan produce juglone, but in smaller amounts compared to the black walnut. Juglone is one of many plant-produced chemicals that can harm other plants in a process known as allelopathy. English walnuts are not as toxic to other plants as is its cousin the black walnut, however, I would still refrain from adding english walnut leaves to a compost pile. - Millet (1,449-)
That is really only Black Walnut. English Walnut should be just fine for compost or mulching (as shredded leaves). My neighbours have English Walnuts and they don't affect anything nearby (birch trees, grass, roses, etc).
Black Walnut is the only one that I have heard is a no-no, I do not know about the English Walnut. Millet seems to feel that neither is good. Leaves from the Southern Magnolia are not recommended as candidates for your compost. Not sure if they are toxic or that they take forever to decompose, they are like iron plate.
