How Far Apart to Plant Onions

Spacing onions correctly is vital to yielding a decent harvest. Plants compete for resources in their given area and if not spaced correctly, the plants will suffer with insufficient water, light, and nutrients. The spacing of onions varies depending on how you initiate the growth process. Spacing for onion seeds differs from that of sets or more developed onion plants.


Spacing Onion Seeds

When beginning with onion seeds, the objective is germination and just enough growth so they are hardy enough to transplant. When your seedlings have reached approximately three-inches tall, you can relocate them to a more spacious container or a garden.

If you are using a large container for the seeds, follow these procedures:

  • Select an area that has a temperature of 68°F (20°C) to 77°F (25°C)
  • The soil should have a pH of 6.0 to 6.8
  • Scatter the seeds evenly over the compost
  • Cover the seeds with another thin layer of compost

You may choose to use a partitioned container that keeps the onion seedlings separate and prevents intertwined roots.

When planting seeds in a garden, they can be sown closely and thinned out after they have reached approximately three-inches high. The seedlings are ready for transplanting when they have three sets of leaves.

Spacing Onion Sets

Onion sets are larger than seeds and require more space. A partitioned container with one set per compartment allows for a more manageable transplant when your sets sprout and develop growth. If you are using a permanent container or planting directly in a garden, space the sets at least four-inches apart. However, if you wish to grow large onion bulbs, you must space the sets approximately six-inches apart.

Spacing Onion Seedlings

Onion seedlings will need to be transplanted when they are four to six weeks old or around three-inches tall. If you opt to purchase onion seedlings, you may begin with this step. Onions planted straight into a garden will require more space to expand and absorb necessary nutrients.

Adequate space between your onion plants makes weed control easier. Additionally, placing your onions in various sections of your garden, rather than one area may reduce the spread of diseases. In a garden, keep twelve to eighteen inches between each row of onions. If you are not planting in rows, keep at least six to eight inches between each onion in all directions.