I don't know if you've gotten any tips on preventing overwatering or not, but thought I'd let you know I determine when to water my plants based on the weight of the pot. Water it one day, then pick the pot slightly up off the floor to get an idea of how much it weighs. Wait at least 3 days, then just go pick it up again. Because you're overwintering, it's probably not taking up water at the same rate as it did before you chopped it down, so it will probably still be pretty heavy. Wait a few more days, then pick it up again. Wait until the container is fairly light (consider the weight of dry soil and the plant, of course) before watering again. Once I've pruned back my plants for overwintering, they generally don't get watered more than once a week - sometimes less. They may need just a tad more often at first while they're in the process of going dormant, but not much. Also, how do you know that resulted from overwatering and not something else?