Onion bulbs (sets) should be planted shallowly to ensure proper bulb development. The recommended planting depth is generally between 1 to 2 inches (about 2 to 5 cm) deep, with the pointed tip just barely covered or slightly showing above the soil surface. Planting deeper than 2 inches can negatively affect bulb growth. Specific guidelines include:
- Bury onion sets 1 to 2 inches deep, spacing them 2 to 6 inches apart depending on whether you want mature bulbs or scallions
- Another approach is to push the set into loose soil just up to the neck, barely covering the bulb
- Some sources suggest planting about 1/4 to 1/2 inch deep, with spacing of 3-4 inches apart
- The Royal Horticultural Society recommends planting sets 2 cm (¾ inch) deep so the tip just shows at the surface
- It is important not to bury the bulbs too deeply; a light covering of soil or compost about an inch thick is sufficient
In summary, plant onion bulbs shallowly, about 1 to 2 inches deep, with the pointed tip just under or slightly above the soil surface, to promote healthy bulb formation and growth.
