Watermelon Day Always on August 3rd. This big fruit deserves it's own big day. And, so we give pause to celebrate watermelons on National Watermelon Day. Sweet and tasty, watermelons are one of summer's favorite fruit. It's standard fare at picnics. While watermelon is over 90% water, it sure tastes good. Please don't limit your consumption of watermelon to just this month. Stores carry watermelon twelve months of the year.