Onions grow best
  in sandy loam or peat soil. The root system is weak, so fertilize
  and water close to the plant. The size of the bulb will be proportional
  to the size of the plant. Water and fertilize well in early stages
  Hints: 
  Start indoors. Transplant 5- to 8 cm [2-3"] apart
  in rows 30 to 45 cm [12-18"] apart. In the fall, bend
  tops to hasten ripening.