For gardeners who are willing to wait for the results, rooting a black walnut cutting is an economical way to propagate trees for the landscape. Hardwood cuttings, including black walnut, take longer than softwood cuttings, but rooting them is possible. Because rooting hardwood is difficult, don't give up if your black walnut cutting does not root the first time around. Try rooting more than one cutting at a time to strengthen your chances of propagation. Patience and special care of your cutting while you wait for it to root will eventually pay off with results.
Take your cutting in the autumn before the first freeze. The cutting should be no bigger in diameter than a pencil and can be up to 30 cm (1 foot) in length. Choose a cutting that has several buds, and snip at an angle with sharp pruning sheers.
Fill a large bin or bucket with coarse sand. Bury the black walnut cuttings deeply in the sand. Keep the bin in a cool, dry location throughout the winter and do not water.
Remove cuttings in the spring. Be careful when locating the buried cuttings. It is best to use your hands to locate the cuttings rather than risk damaging them with a spade.
Insert black walnut cuttings in large pots filled with rooting medium, not garden soil. For drainage, add pot shards or pea gravel to the bottom of the pot before adding rooting medium. Use coarse sand or commercial rooting medium purchased from a garden centre.
Water the cuttings evenly nearly every day. Never let the rooting medium dry out. A successful rooting may take up to two months, after which it may be transplanted.