I have a large-ish unnamed Kousa dogwood that was relatively inexpensive because it’s simply a seedling from an unknown strain, not a known cultivar. So yes, they can grow from seed. But it is not instant, or easy. All I know is that you have to clean off the red pulpy fruit to locate the seeds inside it as soon as the fruit ripens, and then sow them outdoors in a nursery bed or cold frame that’s well-marked so you don’t lose track. Nothing will happen anytime soon. They can take a year or longer to grow, and starting numerous is recommended to allow for losses. The most detailed accounts of this I could find for you are these (one more technically written but extremely thorough, the second more conversational): http://www.pfaf.org/database/plants.php?Cornus+kousa
Welcome! I’m Margaret Roach, a leading garden writer for 25 years—at ‘Martha Stewart Living,’ ‘Newsday,’ and in three books. I host a public-radio podcast; I also lecture, plus hold tours at my 2.3-acre Hudson Valley (NY) Zone 5B garden, and always say no to chemicals and yes to great plants.