In Jain ahimsa-based food practice, onion and garlic are usually avoided because they are underground bulbs and are considered to contain and disturb more living beings when uprooted and eaten. They are also believed to increase kāṣāya tendencies like anger and desire, so they are avoided in satvik Jain food.

Turmeric and ginger powder are often treated differently in many Jain kitchens because they are used in small dried spice form rather than as fresh bulbs/roots. In practice, many Jains accept the powdered spice if it is part of ordinary cooking and not the fresh underground vegetable.

However, please note one important point: practice varies among Jain communities and families. In stricter Jain observance, even fresh ginger and fresh turmeric may be avoided because they also come from underground parts.

So the simple distinction is:

• Onion/garlic: generally prohibited in Jain food.
• Turmeric/ginger powder: often permitted in some Jain traditions as dried spices, though not everywhere.

If you want, I can also give you the Jain reason in very simple one-line form.