Green tomatoes are not poisonous and are safe for human consumption. An heirloom tomato plant produces tomatoes that are green even when fully ripe, while other types of tomatoes are green because they are not ripe. Coating the green tomatoes with a breading and frying them is a popular way to eat them.
The green heirloom tomatoes are sweeter and less tart than the tomatoes that are green because they are unripe. Heirloom varieties are a good source of potassium, vitamin C and vitamin A. Unripe tomatoes also contain these nutrients, but in smaller amounts. They also have a higher acid content than a ripe tomato or the heirloom kind.