Tomatoes are barely poisonous and are generally pretty safe to feed dogs. Most dogs don’t ingest enough tomato plants to cause a problem. Tomato plants are in the Nightshade family and contain tomatine. Tomatine is found in concentrations of up to 5% in the leafy greens, the fruit blossoms, and in small green tomatoes; this concentration rapidly decreases as the tomato ripens. When stems, vines and green fruit are ingested, clinical signs can include gastrointestinal irritation, ataxia, and weakness. Treatment is purely supportive with an overall good prognosis.