What is a marrow plant? I only get links to bone marrow when I try and look it up. I wouldn't go with anything less than 5 gallons of root space for large plants like pumpkins (each plant). I would use a drip system
for large plants like that as well. I prefer coco chips for growing media myself. But if growing in buckets/containers rather than using individual baskets, I add some rock/gravel at the bottom of the buckets/containers for added drainage quality's.