I planted three Carolina Cross seeds purchased from the Burpee display rack at the local big box home supply store and crossed my fingers. If you are not familar with Carolina Cross, they are capable of producing 200 lb watermelons under the right conditions.
We had several days with temps above 100 degrees in my backyard last year. Apparently, the heat was not good for my watermelon-growing-in-a-bag-of-compost attempt. There were days when the watermelon could have benefitted from some additional water throughout the day.
It took two months for the water melon to form the first idications of fruit and another month to reach softball size. In mid-September I picked two or three very small melons with high hopes, but when they were cut open it was evident that my attempt was a failure. They were nearly 1/2 rotten. I think the lack of water must have contributed to the poor results. I watered through the slits cut into the top of the bag by inserting a water hose for about 3 minutes, but some days the soil was completely dried out by mid-afternoon.
I don't have space to plant the melons the traditional way - in hills. The plant-in-a-bag technique sounded perfect. Maybe I'll try it again this year (or maybe not).