Here is a list of ideal growing conditions for onions:
- Full sun
- Fertile, thoroughly dug, well-prepared soil
- Ideally apply manure several months before planting as growth is too lush if the soil is freshly manured
- Wood ash is good for onions, but not ash from coal fires
- Good drainage is essential
- Check pH – ideally 6.5 or above for mineral soils, 5.8 for peaty soil
- Don’t grow in the same bed more than one year in four
- If you are bringing/buying-in soil check that it doesn’t come from a place where onions have been grown in the past, or you might get white rot or other diseases and pests. Commercially, onions are grown on silty, sandy loam or peaty soil; you should definitely avoid heavy soil (high clay content) and stones