Pack potting soil into the bottom two-thirds of 2-inch starter pots. Fill a pot for each purple millet plant you want to grow.
Spritz the potting soil in each starter pot with a spray bottle. Keep spraying the soil until the top half is moderately moist.
Sow four purple millet seeds in each starter pot. Place the seeds on the soil in the pots. Cover the seeds with a 1/2-inch-thick layer of potting soil. Mist the top layer of soil with the spray bottle to settle it.
Set the starter pots on a warming mat with the temperature set to 68 degrees F. Lower the temperature to 59 F at night to mimic outdoor conditions.
Mist the potting soil in the starter pots whenever the surface dries out. Mist the soil just enough to moisten it to a depth of 3/4 inch.
Watch for sprouting in two to five days. Remove all but two of the purple millet seedlings from each starter pot. Leave the largest and healthiest seedlings in the pots.
Move the starter pots to a bright, sunny windowsill once they germinate. Keep them moist and warm until one week after the last frost in spring, then plant them 12 inches apart in a sunny bed, once soil and air temperatures warm to 65 degrees F.