I grew watermelon once in New York. I managed to produce one meager melon that was small and wasn't particularly good. I have tried to grow mellons for the past two years in Texas. I didn't even get flowers.
This year I added some melons as an afterthought once we got soil for the cement planters (some time in July). Right now the count is FOUR watermelons! Not sure what I did differently, other than using a container, but clearly it's working.