Question
can you grow a watermellon plant in a large container

Answer
Sure! the root system isn't that extensive on melon plants, but if you don't have room to let it run (it can stretch outwards of 8 feet!)..then you will need to build a support structure for it to climb , like a tee pee or trellis type structure. Use a good potting mixture (no additives) and keep well watered, plant 3 seeds and then keep the 2 strongest. Use the smaller varieties, (smaller melons), for the larger ones will require way too much space. Nick