Book 29, Question 124
Is banana peel or cooking water good for plants?
Banana peels contain potassium, but they take time to break down, so it's best to bury them in the soil or compost them.
Water from boiling or steaming vegetables, once cooled and unsalted, has a few nutrients and can be used to water plants. But these are tiny boosts, not replacements for good soil and compost. Never use water that has salt or oil.