When I went out yesterday and pulled up our drowned bell pepper plant (see Our Mastiff Helper ) this came up along with it:
It's a clump of mushrooms that had been growing undetected under the mulch. Digging around a bit more, I noticed that the soil was very moldy and smelled mildewed. After seeing and smelling this, I decided that replacing all of the soil was probably the best thing to do. So I transplanted the Jalapeno plant to another container, and threw the Mortgage Lifter tomato plant into the compost bin. The tomato plant had turned yellow and pretty much stopped growing. Like the bell pepper plant, its roots were also completely white with mold.
This time around I enlarged the barrel's drain holes quite a bit and I think I'll leave off the mulch. If, by some future accident, it receives an overdose of water again I want it to drain quickly.