Flowering dogwood trees can successfully be grown by a home gardener from seed, which is the chief means of propagating the trees. While you may not get the exact varietal or tree you intended, you will get a flowering dogwood tree. When collected fresh and properly cleaned, dogwood seeds can be planted directly into the garden soil in the fall. Flowering dogwoods are fast-growing trees, but it will still likely take four to five years before a dogwood grown from seed bears bloom.
Collect fresh dogwood seeds in the late summer or fall as the blooms drop and the berries or seeds turn bright, shiny red. Pick the seeds when they are at their peak maturity and come loose from the tree when barely touched or pulled. Lay them out on a stack of old newspaper or some other slightly absorbent surface and let them soften up a bit over four to seven days.
Soak the red seeds in plain water for 24 to 48 hours to loosen the red coating. Rub off the softened red pulp by holding the seed between your fingers, and drop the clean seed into a fresh glass of water, where healthy seed will sink to the bottom and unhealthy seed will float. Scoop off the flotsam and lay out your healthy seed on a new layer of newsprint to dry.
Scarify the dogwood seeds to increase the odds of germination by using your garden knife to nick the coating of the seeds in one or two spots on each clean, dry seed.
Plant the clean and scarified seeds immediately in a well-tilled, moist soil bed, approximately 1/2 inch deep and at 2-inch intervals. Plant at least three times the number of seeds as you would like in saplings to allow for seed failure. Mulch with compost or fine shredded bark to hold in moisture. Mark the planting spot clearly to remind you and give a heads up to others of what's growing.
Water the soil around the seeds to keep it evenly moist without disturbing the seeds. If there is winter drought in your area, occasional watering may be helpful. In the spring, when pale shoots of the seedlings appear, water very carefully by hand from a tiny pitcher or glass to prevent their tender roots from being disturbed. Water the seedlings once or twice each week, and compensate for excessive or no rainfall as necessary. Irrigate throughout the summer and fall so that the soil remains moist and the seedlings are never under drought stress.