Back to all articles



Onions are a species that are highly influenced by their plant density, particularly in terms of their shape and size. Onions that are grown at above optimal density, may be misshapen, may not grow to their full size potential and will mature later than expected. Onions that are grown at low densities, can exhibit an increased percentage of visible doubles and give a reduced yield.

In general, 80 bulbs per m2 is a reasonable target, although the optimal density for any particular circumstance depends on the variety, season and location. Here's a way that you can calculate your final onion plant stand, given variable germination, bed width and seed spacing.

Onion plant density(per m2) =

(Seed Label germination % x 9) x number rows per bed
------------------------------------------------------------------------------(actual bed width (m) x in row seed distance (mm))

Notes on the equation:

  Seed label germination - straight from the pack.

  9 - a field factor, assuming 90% of seeds that are sown, survive, remembering that label germination results are from tests carried out in optimal germination conditions.

Number of rows per bed - four double rows, would be entered as eight rows and so on.

Bed width - measure the width of the top of the bed, in metres. This is not centre to centre, but the actual width of the bed.

In row seed distance - distance between seed in each individual row, in millimeters.


For example, if you had an onion variety with a germination of 85%, sown in four double rows, on a 1.5 m wide bed with an in-row spacing of 50 mm, your final standing plant density would be 81.6 bulbs per m2, calculated as follows:

Onion plant density(per m2) =

(85% germination x 9) x 8 (four double rows)
(1.5 m wide bed x 50 mm between seeds)


To get number of bulbs per hectare, simply change the bed width to centre to centre width and multiply the result by 10 000. As a check, if the centres bed width was 1.8m, the result from the figures above would be 680 000 bulbs per hectare.



by: Bruno Tigani
Grower Solutions Magazine
Lefroy Valley Magazine

June 2003

  Bookmark and Share

top of page  

to all articles  


AgriSupportOnline, Moshav Almagor, Israel
Legal Disclaimer