Early Onion Harvest Options In the Pacific Northwest

In the U.S. Pacific Northwest, onions are typically direct seeded in February through  March, harvested from late August through October, and marketed out of storage from October through March. An earlier harvest could be advantageous for processors, increasing the period when locally produced onions are available. Research at the Oregon State University Malheur Experiment Station evaluated whether earlier harvests might be possible by producing bulbs from transplants and sets. Transplants could be produced in the winter and planted in March. Transplants produced in unheated “low tunnel” cold frames had inferior performance compared to transplants produced in a heated greenhouse. Transplants produced from field-grown over wintering varieties performed inconsistently. Onion bulb production from greenhouse-grown transplants or transplants from Arizona can be harvested 4-6 weeks earlier than bulbs from direct seeding.  In 2010, 13 onion varieties were evaluated for bulb production from transplants.  Averaged over the 13 varieties, the first harvest in mid-July  yielded 56 Mg/ha of marketable onions.  Yield increased over time, averaging 80 Mg/ha on August 3.  All varieties had more than 80% single centered bulbs on all three harvest dates. An alternative to early onions from transplants is to produce onions from sets.  One advantage of onion production from sets is the ease of mechanical planting compared to transplants. Onion sets are susceptible to bolting from exposure to cold temperatures after planting. Onion sets were produced by sowing seed very thickly one year, resulting in very small bulbs (or “sets”). These sets were harvested, stored over the winter, and planted the following spring. Our research demonstrated the potential of some varieties for bulb production from sets. In 2010, 11 varieties were evaluated for bulb production from sets produced in 2009.  Averaged over the 8 long-day varieties, the first harvest in mid-July  yielded 51 Mg/ha of marketable onions.  Yield increased over time, averaging 62 Mg/ha on August 3. Some varieties had little bolting.  All long-day varieties had more than 80% single-centered bulbs.