We plant our carrots in a raised wide row of about three feet wide. Then we put the carrot seeds in an old spice bottle with a shaker top. Put a teaspoon or so of sand in with the seeds, mix, and then just shake over the row. Cover them up by just pulling a light cover of soil up from the side of the row with a rake. Never tried onions like this (we start ours indoors in Feb.) but I bet it would work in the right growing zone.