The onion and related members of the onion family have been around for a long, long time. The pyramid builders ate them, and Alexander the Great fed his troops with them. Soil Onions are best adapted to loose, friable soils. Compacted and poorly drained soils are not suitable for onions. Hard or compact soils restrict bulb size and uniform shape.
Onions also require high fertility because they are heavy feeders.
Broadcast and incorporate fertilizer or manure before planting. Base the amount and kind of fertilizer on soil test results. Start them early regardless of the method. Frost will not hurt them, so put them out as soon as you can work the soil. The nature of onions is to grow tops in cool weather and form bulbs in warm weather.