In Jainism, onions (and other root vegetables) are avoided mainly for two reasons:

• Non-violence and purity of mind: Jains strive to minimize harm to all living beings. Root vegetables are often associated with more tiny organisms living in the soil, and uprooting the plant can harm many beings that dwell in and around the root. Avoiding them reduces accidental violence.

• Discipline and spiritual focus: Certain foods, especially those that “animate” or intensify passions, can disturb meditation and restraint. Onions are traditionally considered to stimulate passion and disrupt calm, which is undesirable for ascetic and devout practice.

Traditional texts and practices in both Digambar and Shwetambar communities generally discourage eating roots, including onions and garlic. There can be some practical or regional variations in everyday lay practice, but the underlying aim remains the same: minimize harm and maintain spiritual clarity.

If you’d like, I can summarize the specific verses or provide a simple, traditional summary from Jain scriptures on this topic.