Which type of soil is best for planting onions?

Onions grow well in well drained soil with pH levels between 6.0 and 7.0. Soils organic matter can be increased by adding well rotted manure or compost in the spring or fall season. Onions grow well in slightly acidic, fertile and well drained soils. Heavy soils can be improved by incorporating organic matter like compost in to the soil. Onions need higher fertility levels.