#gardening watermelons.I have never seen square watermelons. Very interesting!1. Watermelon seeds (Try Sugar Baby variety)2. A square container 3. Plenty of sunshine and water 4. Grow Watermelons from seed: Plant your watermelon seeds 2-3 weeks after the last frost. Seeds should be planted about one inch deep in soil. Sow 2-3 seeds per hole.Once your watermelons begin to grow from the vine, you can transplant them into your square container. Your watermelon must be able to "breathe.