Walnut leaves produce juglone, a chemical that can be toxic to other plants, according to horticulturalists from Virginia Tech University. Black walnuts contain high quantities of juglone and must be composted separately from other organic matter. But the juglone levels in English walnut leaves is low enough that it should be sufficiently neutralized by regular composting, according to Tom Rood, with Cornell University.
Chop the leaves into small pieces by running over them with a mower equipped with a mulching blade or by raking them into piles and chopping them with a hoe. The leaves will compost more quickly if broken into small pieces.
Layer the leaves in the compost pile with other organic matter, such as kitchen scraps or grass clippings. Leaves are naturally high in carbon, which composts slowly. Layering in high-nitrogen matter such as grass and vegetable peelings will speed composition and increase the temperature of the compost pile, which will break down the juglone more quickly.
Water the compost pile to keep it moist but not soggy. Moisture encourages the growth of organisms that speed decomposition and hasten the transformation of the leaves to healthy compost.
Turn the compost pile regularly to aerate the contents. This also hastens decomposition.