Question for an Expert

I have been growing hairy vetch as a nitrogen fixer alongside some other potted plants, like fava beans for example, which have since been harvested. The hairy vetch continues to grow, I suppose as a green manure? If I am to use this same pot come spring, do I trim the hairy vetch or pull it out? I don't want to make a mistake by removing the valuable root system, but I am also not clear if there will be sufficient room in the soil for a new plant? This article addresses some of this. http://garden.org/learn/articles/view/122/