Maximizing Onion Bulb Dry Matter Content

The majority of onion crops are grown for the fresh market. Bulbs should be sufficiently dry for the intended purpose. Most common bulb onions have 10-12% dry matter. Onions grown for dehydration require higher dry matters of 17-20%. Nitrogen and potassium are the most important nutrients influencing dry matter content of onion bulbs.

Crop Nutrition and Onion Bulb Dry Matter

Nitrate x ammonium nitrate

Trials confirm that a balance between nitrate and ammonium-N is most effective at promoting onion leaf and bulb growth. However, during later stages of growth, nitrate forms provide higher dry matters in the bulb.


Potassium is particularly important where high N rates have been applied (if high yielding systems). In these situations, increasing dry matter and sugar accumulation in the bulb helps maintain yield.