Onion might keep your plants from getting sicknesses!
Onions are very healty vegetables, with antiviral and antibacterial properties. Normally, you can't get red onion seeds, but you can get shallots, red bunching, white bunching, and yellow/white ones. Red onions are eaten raw more often then yellow ones. Soaked in vinegar in a salad tastes very good.
Scatter some onion seeds on the ground, or bury the seeds ¼'' deep. Or you can start them inside, in moist seed starter in a yogurt container. The seeds should sprout after 7-15 days, depending on the type. And the onions will normally take 90 days to a few years to grow. If you want to have very flavorful onions, try growing one for a few years. THe onion will probably not be very big, but it should be very flavorful.
Onion seeds are small, but not as small as basil seeds. Onion seeds are not round, but some obscure shape, a little like a short and stubby ice cream cone. When collecting seeds, wait until the seeds are almost falling off the flower.