Black walnut trees are a majestic addition to the home landscape, providing shade on hot days. Although black walnuts are slow-growing, they eventually grow into a massive tree reaching up to 100 feet high. Although most home gardeners don't want to cut them down, black walnuts often are planted as an investment because their hardwood is extremely valuable. Black walnut trees take a bit of tender-loving care during the first couple of years, but after that, they'll grow with very little attention.
Decide where you want to plant the black walnut tree. Black walnut does best in rich, well-drained soil. Make sure the soil is deep and workable, at least 3 feet down so the roots have plenty of room to spread without hitting hard clay or bedrock. It helps to enrich the soil by adding a few shovels of compost. Keep in mind that black walnut trees emit a chemical that is toxic to many other plants, so choose the planting site accordingly. Plants that are compatible with black walnut include dogwood, sugar maple, begonias, crocuses, bluebells, ferns, daffodils, Kentucky bluegrass, iris and Shasta daisies.
Purchase a bare-root black walnut sapling from a nursery or greenhouse and plant the tree as soon as possible. Dig a hole that is large enough to accommodate the tree's root system, but not too much larger. Put a bit of loose soil in the bottom of the hole. Ask somebody to hold the sapling over the hole. The crown, which is the point where the roots meet the sapling's trunk, should be just below ground level. Shovel soil under and around the roots until the tree is supported, then pour a bucket of water in the hole. Finish filling the hole with soil, tamping it down lightly as you go.
Spread a layer of mulch around the tree immediately, but don't allow the material to touch the tree. Mulch can consist of dead leaves, peat moss, straw or newspapers.
Water the sapling regularly, especially during the first growing season. Feed the sapling a good all-purpose, slow-release fertilizer, but be careful not to over-fertilize; doing so will cause the tree to grow too quickly, making it more susceptible to freezing during the first winter.