Short answer:

• On many tithis (lunar days), including Amavas (new moon) and Poonam (full moon), Jains often limit what they eat to reduce harm to living beings and to practice extra restraint. A common practice is to avoid green leafy vegetables on those days, and some people also restrict certain other foods. This is a tradition that varies by family or sangh, and by Digambar vs Shwetambar communities. Root vegetables are generally avoided as a broader Jain rule, but the greens restriction on specific tithis is a further, tithi-specific practice. ( jainknowledge.com, jainworld.jainworld.com)

Key ideas in simple terms:

• Amavas and Poonam are part of the monthly tithi cycle. Many Jains observe extra restraint on these days.
• Common tithi practice: avoid greens (green leafy vegetables) and sometimes avoid fermentations or dairy, depending on local guidance.
• Root vegetables are usually avoided in Jain practice anyway, for reasons of ahimsa to tiny life forms; the greens ban on certain tithis is an additional rule on top of that. ( jainworld.jainworld.com, jainknowledge.com)
• If you follow a specific tradition or temple, check the local maryādā (guidelines), as Digambar and Shwetambar communities can differ in the exact items permitted on Amavas/Poonam. ( jainknowledge.com)

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