Fill a low pan or tray with an inch or two of sterile potting soil. Choose a small tray that fits inside a plastic bag to retain humidity.
Place the golden barrel cactus seeds on the surface of the potting soil and cover with a half-inch of sand. Place the tray in a clear plastic bag to retain humidity around the seeds.
Keep the seed tray in a sunny spot where temperatures stay about 75 degrees Fahrenheit throughout the day and night. Wipe any condensed moisture from the inside of the bag. If this moisture drips into the sand, it makes the seeds too wet and causes decay.
Dig small holes in the sand. Add water to the tray through the holes in the sand to keep the potting soil evenly moist. Keep the potting soil moist and the sand dry for best results.