The best fertilizer for growing watermelons is a 5-10-10 mixture in the beginning and a 33-0-0 mixture towards the middle of the watermelon growth cycle. The best mulch for growing watermelons is a mixture of straw, grass or shredded newspaper.
The 5-10-10 fertilizer mixture creates a healthy foundation for watermelons to begin growing, while providing enhanced soil fertility. Mulch that is made up of either weed-free straw, shredded newspaper or grass clippings can be added after the foundation is laid to nourish seeds and deter weeds. As watermelon vines start creeping along the ground, a 33-0-0 fertilizer mixture is applied to all rows to boost watermelon growth and size.