Onions are seeded on beds of varying width, depending on the cropping system and the equipment of the individual grower. Use a bed width of 26 to 44 inches (from center to center) with two to four seed rows per bed. Uniform seed placement and in-row plant spacing has a major influence on bulb size and is critical to a good stand establishment. Seeds should be planted 0.5 to 1 inch deep. Avoid wide spacings which promote large bulbs with thick necks. Generally, an in-row spacing of 3 to 4 inches ensures both high total yield and a higher percentage of onions in the jumbo (3.0-3.5”), large jumbo (3.5-4.0”), and colossal (4+”) market classes.
Many types of planters are used to seed onions and all must be carefully set to maintain proper seeding depth and rate. A ‘small seed’ type planter with short seed drop is recommended. Vacuum and other types of precision planters can be very effective at controlling plant spacing and reducing the amount of seed used.