In Jain Dharma, the main basis of food rules is ahimsa (non‑violence) and control of passions, not taste or culture.

1. Root vegetables in general (ideal rule)

According to strict Jain principles:

• All root vegetables (kand‑mool) – potato, onion, garlic, ginger, etc. – involve more himsa because:

- The whole plant is usually destroyed when uprooted. - Roots are believed to have many more living beings (nigod jeev) in and around them.

• So, from the purest point of view, even ginger should be avoided.

This is the ideal followed strictly by Jain sadhus/sadhvijis and many very‑careful householders.

2. Why onion and garlic are especially avoided

Onion and garlic are treated as worse than other roots, for two reasons:

1. More life‑forms

Jain texts and traditions classify onion/garlic among those roots that contain anant pranas (countless lives) and involve comparatively higher violence.

1. Effect on the mind

They are considered tamasic/rajsic: - Agitate the mind - Increase krodh, maan, maya, lobh and sensual passions - Disturb sadhana, prayer, and concentration

So for a spiritual seeker, they are doubly avoided – high himsa + disturbance of inner purity.

3. Then why do many Jains eat ginger?

In everyday grihasthi (householder) practice, some leniencies developed:

• Ginger is seen as:

- Relatively less himsak among roots - Often used in small quantity as a medicine or flavoring, not as a main item - Botanically, it is a rhizome from which the plant can regrow, so people feel the plant need not always be fully destroyed (though in farming it usually is).

Because of this, many Jain families allow limited ginger, while still:

• Completely avoiding onion and garlic, and
• Avoiding many other roots as well, depending on family/sampradaya.

4. Difference in practice

• Principle level (Jain shastra / munis):

Best is to avoid all root vegetables, including ginger.

• Practical level (many householders):

- Onion and garlic: strict “no” - Ginger: often allowed in small quantity, sometimes discouraged by more strict families.

So, it is not that shastra clearly says “ginger is permitted, onion/garlic are not.” Rather, all roots are higher‑himsak, but onion/garlic are especially avoided due to very high violence and strong passion‑increasing nature, while ginger has been practically tolerated by many as a milder exception.

You can read a related explanation here