University of Idaho Extension

Specialty Crops: Onions

Onions are grown primarily under furrow or drip irrigation in southwest Idaho and are a high value crop.  Most of the harvested onions are  marketed from storage during the fall, winter, and early spring.  they represent roughly a third of the onions marketed nationally. Fertilizers historically are used extensively.  Onion culture presents special challenges for effective nutrient management.  The root system is relatively shallow though roots extend well into the second foot.  The soils program at Parma has addressed onion fertilization issues since the 1970s.

Furrow irrigated onions are commonly grown in double rows spaced 3-4 inches apart and centered on 21-22 inch beds formed typically in the fall.  Onions are early spring planted after the beds are harrowed.  With furrow irrigation, every other corrugate is normally wetted as shown in the picture to the right.

Southern Idaho Fertilizer Guide - Onions

Much of our local research on onions is used for the revision and development of the Idaho fertilizer guide.  The guide provides general recommendations for nutrient management based on pre-plant soil testing. 

Nutrient Management for Onions in the Pacific Northwest

A compilation of nutrient management information from onion research workers throughout the Pacific Northwest. 

Relevant Publications

Nitrogen and Onions

Nitrogen sufficient onion (left) and nitrogen deficient onion (right). Parma, ID. Photo taken by Amber Moore, University of Idaho.


Phosphorus and Onions