Personally I wouldn't grow watermelons in a container.

How high are these containers. My concern with melons and containers is the fruit is heavy and hanging in midair they are liable to either break off or pull the plant out of the container. Watermelons need lots of water--are you going to be able to give them enough in a container. In addition you would have to devise some kind of net to support the fruit. You could plant more than one seed if you are going to do it

Especially the large ones. In addition the large ones will need more root room than a container can give them.

I agree with oilpainter that unless you can rig up a way to support the fruit watermelon in a container will be very problematic.

But if you want to give it a try then the bigger the container the better and both of yours are quite small. The 24" container would be close to the size of 1 hill in the garden except for root room so it could hold 1 plant perhaps. But you will have to water it several times a day and feed it at least weekly for any production.

Container gardening is great in many ways and normally easy to do but a few fruits and vegetables just aren't "container-oriented". So rather than things like potatoes (you other post) and melons why not focus instead on food plants that will thrive in containers?

Dave

My Watermelons always sprawl to 15' or so, if you have that much land,why a pot ???

But anyway... Unless you are doing trellis's (in which case you WOULD have to figure out a way to support your melons), all you need to do is pinch off any watermelons that will be in a position to "hang"...VIOLA...back in business ;-)