Jains avoid potatoes (and other root vegetables like onions, garlic, carrots, beets, etc.) mainly because of ahimsa—non‑violence.

• Uprooting kills the whole plant: To eat a potato the entire plant must be pulled out, which destroys that life completely.
• Many tiny lives are harmed: Soil around roots teems with countless micro‑organisms; pulling and cleaning roots disturbs and kills many of them.
• More chances of hidden life: Roots store moisture and nutrients, so they more easily harbor and generate micro‑life compared to above‑ground produce.
• Simpler, purer diet: Avoiding roots supports restraint and carefulness in eating, which helps spiritual practice.

Traditions

• Both Śvetāmbara and Digambara acharyas guide laypeople to avoid root vegetables; monks and nuns strictly avoid them.
• Regional household practices may vary in strictness, but the ideal remains minimising himsa.

For a short, easy explanation, see: and a simple list-focused note here: .