I've grown pumpkins in a wine barrel on my deck for the past 4 yrs or so - last season, it didn't do so well. I'm thinking that the soil might have a disease. Is it ok to take the dirt out and put new dirt in or will the disease persist in the wood of the barrel - would it be helpful to scrub it clean with hot soapy water? And can I use the dirt somewhere else?
It could be that the dirt is depleted of the nutrients that pumpkins need. I'd put new soil in, add the old soil to other containers (not all in one, but divided between several), and see what happens. Diseases show up as deformed, off-color, or dead leaves and stems. If this is what happened, move your pumpkins to another container and plant something not in the same family (cucurbita, which includes squash) in the wooden barrels. If you want to try to clean the barrels, try a 10% solution of chlorine in hot water (a cup of bleach in 9 cups of hot water). I'm not sure this would destroy any disease organisms, though.
The pumpkins would start to grow & then when they got to about 1 or 2 lbs, they would just rot & die...
If it's just depleted, then enriching it would be good. Just keep an eye on it to make sure it's not diseased.
Not only is it possible there aren't enough nutrients, a pumpkin is a huge fruit to grow in a container, needing a continuous supply of water. If it wilts even once you may be stressing it enough to abort its fruit. If water might be part of the problem, try adding some of those soil moist crystals or even... a diaper(the whole thing or tear it open and mix the lining contents into the potting mix and water it in). Both will hold copious amounts of moisture for the plant.
I've actually grown them successfully in the wine barrel for the past 4 or so years. It does require a lot of watering but its kind of fun because the vine is so beautiful sprawling across the deck and you can arrange the pumpkins so that they sit upright and grow perfectly round.
Like others said the soil was probably depleted. It might have also started compacting. I found this happened to a couple of my orchids this winter and I had to start over with new bark. Why take chances and start with new soil after scrubbing the barrel with a little bleach in water to sterilize the container? Your beautiful leafy greenery and vegies would be a shame to miss and you'd be good for another several years. Happy gardening whatever you decide to do.