Watermelons need watering at least 1 inch per week. Set them out in well-drained soil. Yellow patch on the top of the melon are not disease, but instead sunburn; if you see it, cover the fruit with a basket or cloth. Watch the plant for clues as to optimum maturity. Inspect the curly tendril near where the watermelon attaches at the stem. It should be dead or brown. When the watermelon matures, this coloring will dull.