Cornus is a genus of trees and shrubs, beloved for their flowers and the color they provide to the autumn landscape. Cornus florida, commonly known as flowering dogwood and Cornus kousa, the kousa dogwood, are among the more commonly planted of all flowering trees, according to horticulturist and woody plant expert Michael Dirr. Dogwood seeds are embedded in the tree’s fruit, which is a drupe. Most dogwood tree fruit ripens in fall, although some, such as Cornus alba, ripen in summer. Most dogwood trees are hardy in U.S. Department of Agriculture plant hardiness zones 5 through 9. Kousa dogwood is hardy in USDA zones 4 through 8.
Harvesting Ripe Seed
As soon as the dogwood’s flowers begin to drop, the tree starts producing seed. When the seeds begin turning red in late summer, keep an eye on them, because they are just about ready to be harvested. The test for ripeness is something the older kids might enjoy helping with -- squeeze the drupe; if the seed pops out, it’s ripe. If you wait until the drupes fall from the tree, you’ll need to move quickly or the squirrels may beat you to them. If a gentle tug doesn’t remove the seed from the tree, allow it to remain for a week or two because it isn’t ripe yet. Be aware that the dogwood fruit is poisonous to humans if consumed, so take precautions if small children are present. Wash your hands after handling dogwood fruit.
Cleaning the Seeds
In nature, the seed’s outer layer of pulp is worn down by the elements, so to germinate them indoors, you’ll need to manually remove it. Soak the drupes in a bucket of water for 24 hours and remove any that float to the top, since they aren’t viable. Use your hands to squeeze the seed from the drupe. You may need to use a small toothbrush or other type of scrubber to remove any pulp that remains clinging to the seed. Lay the seeds on newspaper to dry. Dogwood seeds retain viability for two to four years.
Nature also has a way of dealing with the dogwood seed’s hard outer coat. It may be worn down by the elements or by passing through the digestive tract of a bird that consumed it. To mimic this treatment, store the seed in a handful of moist sand, placed in a sealed container and set in the refrigerator for three months. Both the flowering dogwood and kousa dogwood germinate readily after this period of cold stratification, according to Dr. Dirr.
Choose a planting site that receives at least six hours of sun each day and loosen the soil with a gardening fork, shovel or other tool. Rake the bed smooth. Scatter the dogwood seeds over the soil and cover them no deeper than ¼ inch with soil. Water the bed carefully to avoid disturbing the dogwood seeds and keep the soil moist while the seeds germinate. This should occur by late spring.