Remove the pit from a ripe plum and clean off all fruit flesh
Dry the pit for a few days
Crack the hard outer shell carefully to extract the seed inside, if possible
Place the seed in a damp paper towel or moist peat moss
Put it in a sealed plastic bag or container
Refrigerate it at 34–40°F for 8–12 weeks
Check periodically to keep the medium moist, not wet
Plant the seed in a pot with well-draining soil after it sprouts
Cover it lightly with soil
Keep the soil moist and place the pot in bright light
Transplant outdoors after the seedling is strong and frost risk has passed