The black walnut is prized for its timber, its use as an ornamental tree and for its nuts. Heavy cutting has reduced the population of the large black walnut trees that grew for over 200 years with massive 6-foot wide trunks. You can propagate any tree from the nuts it produces so long as you take the time to fulfill its requirements for breaking dormancy. The black walnut tree grows in areas that have at least 140 days of frost-free weather, but needs at least 90 days of cold. It tolerates most soil as long as it is well drained and moist.
Collect the largest black walnuts from under a healthy black walnut tree and place them in a 5-gallon bucket. They will fall in September and October, depending on your location. Pick at least twice as many as you plan to grow since germination is not always successful.
Fill the bucket with enough water so that the walnuts can float, but throw away the ones that float because they are not good and won't sprout. Do not throw any parts of the black walnut into your compost pile since they contain a substance that inhibits growth in plants.
Let the nuts soak for several hours before you try to husk them. Use a pair of heavy-duty rubber gloves and peel off the outer husk. The sap in the black walnut is used as a stain and will not come off your hands or anything else it gets on without a great deal of work.
Place the cleaned nuts into a coffee can filled with damp sand. Close it up and place it in the back of your refrigerator where it can sit for the next three to four months. This will break the cold dormancy of the seed.
Remove the can from the refrigerator and inspect the walnuts for spouts. Sometimes they start early, but not consistently. Plant them in regular potting soil about 3 inches deep in single containers, or at least 4 inches apart from other walnuts in larger containers. Place in a sunny and mild (50 to 60 degrees F.) place to grow.
Expect to see growth from half the planted walnuts in about 4 to 5 weeks. You can move them outside to a permanent position in the late spring. They need full sun and should be several hundred feet away from a forested area, or squirrels may dig them up.