Question
I am trying out my first garden. I had a few vines of watermelon in a pot that grew to about 7 inches but now they are starting to die. Am I doing something wrong. I water them everyday.They get about 4 hrs worth of sun in the morning on my porch. I can not plant them in the soil, I do not own a yard. I live in St. thomas VI, and it is always warm.

Answer
There are many things that can go wrong, when it comes to growing watermelon. I don't think it is the light that is killing it, but they normally would require full sun, about 8 hours or more. If the container is too small, or too large, it may be suffering from lack of water covering the entire root area. If the container is too small, the water has very little soil to hold it, so it just passes by the roots and out the bottom. If the container is too large, the water travels to the edges of the container, leaving the roots dry.
How is the soil drainage? If you used a heavy garden soil, and not potting soil, then the plant will suffocate from lack of oxygen. If you over water, the plant will drown from lack of oxygen. If you over fertilize the plant roots are not able to use all of the nutrients and the roots will burn, and die.
Watermelon will grow in a container, but even if you do everything right and it blooms and fruits, it will not be the same large melon that you see in the store. It will be half the size and possibly less flavor. This is because it is difficult to cultivate the same soil conditions in a container, that the plant needs.
I have grown many garden vegetables in containers with a great deal of effort, and marginal success, but I find vines are the most difficult to grow to production.
Perhaps it would be better to try something easier to manage.