LivingParadise..., one more question. You said you tried growing in containers. I'm wondering how did it go? I'm running out of space but would still love to grow watermelons every year so I'm thinking if growing in containers would work? Probably like a 15 gallon container. Thanks!
Keep in mind, sometimes plants put too much energy into leaves to the detriment of fruit. But since you posted this in the vegetable section and not the fruit forum, I thought that meant you were planning to eat the leaves. Mind you, I have not found reliable sources that definitively state whether watermelon leaves are edible, or that they are poisonous, so try at your own risk (and if you do, please report back!). So whether you want bigger leaves or not might be subject to some debate, if it results in smaller fruit. Again, if the issue is water, more water might simply be the solution - not less sun. But that is not good if a region is drought-prone.
Container growing watermelons is from my experience doable but I guess a bit unusual - all the more so my decision to do so indoors since I got very strong tropical sun in my windows to do so, but could lower the humidity a bit by having them indoors. So it depends on what you're aiming for. The roots can get to about 2ft deep, but most of them are within the 1st foot of soil, so I don't think they really have to go that far down. Watermelons would prefer to spread wide than deep, a bit like strawberries. I did not try to grow them as a year-round crop, merely seasonal, so I wasn't looking for the plant to survive forever anyway. I put it in a shallow window box type plastic container. The fruit would grow on the vine, outside the box. A 15 gal container is only necessary if you really need the container to hold the watermelon itself, or want to try to provide for those few deeper roots. I have written a bunch on the fruit forum about my experiments in container growing, but it's worth noting here too that I like to grow in non-biodegradable styrofoam peanuts, with only 1/3 of the container actually being filled with (good organic) soil. For most plants, that is enough. They really like the air and drainage the styrofoam pieces provide, and it's a good way to recycle something that otherwise is destructive to the environment to grow plants. This cuts down on the need for expensive heavy soil or rocks, and makes the containers really easy to move around. If you grow one with a watermelon in it, the watermelon will weigh the container down against the wind if you grow it outdoors. Although I abandoned the watermelon project because of water consumption, which is expensive here, if I were to try it again in any serious manner I would grow in my 10 gal plastic grow bags, which are super cheap, and allow the roots to grow any which way they want.
Note that watermelon rind is fully edible, as are the seeds, for anyone looking to add to the food value of their crop. It's not easy to grow one's one food, so best not to waste any when it finally reaches maturity!
Some people like to pickle the rind like a vegetable.