Cornus kousa is a form of dogwood also called the Japanese or kousa dogwood and is a small deciduous tree growing in areas where winter gets cold. The primary use is as an ornamental tree with flowers in spring and is propagated by seed, softwood or hardwood cuttings and air layering methods.
Collect seed from a mature tree during autumn. Seeds form in clusters inside fleshy berries that birds love making it a challenge to collect. Harvest when the stone pops out of the fleshy encasement when squeezed, and avoid seeds from trees where there is only one tree in the vicinity since there must be other trees to pollinate the seeds and make them viable. Wash the seeds of all pulp and then put them through a stratification process exposing it to cold temperatures at 4.44 degrees Celsius or lower for three to four months. Either plant the seeds in fall to stratify during winter outside or place them in a plastic bag with damp sphagnum moss and store in the refrigerator until spring. Seeds germinate in two to three weeks when placed in potting medium in pots and in indirect sunlight. Transplant in spring to a permanent area. It takes about seven years before the tree actually flowers.
Take softwood cuttings in early spring from an established tree. Softwood is what starts to grow first in spring and is still green and pliable. Cut 4 to 6 inches on a slant right below a node or where a leaf grows and remove the lower leaves. Dip the end in rooting hormone and insert into a 3- to 4-inch pot filled with coarse sand one inch apart. Cover with plastic to create humidity, and keep the sand moist and place in shade for seven to 10 days, then move gradually to an area with indirect sunlight. When roots reach 1 inch long, the cutting is planted in soil.
Cut 6-inch sections of a branch after the host tree goes dormant in autumn. Cut right above the bumps on the branch indicating a node. Scrape the bottom of the cutting, dip in rooting hormone and insert into a 10-inch hole in the ground with other cuttings upside down. Cover so that they sit 3 inches below the surface and the cutting will callous and might develop roots over the winter. Dig up after there is no danger of frost and insert the bottom halfway into the planting medium. Leaves should grow in two to three weeks and the plant is transplanted in fall or the next spring.
Layering commences in spring by cutting a branch and peeling back the bark to expose the inner core of the plant. Apply rooting compound and wrap the whole area with sphagnum moss then plastic. Roots form in the wound and the branch is cut and planted in shade the first year, then moved to a permanent location the next.