Question
I recently transplanted my tomato plant to a bigger pot and then went away on vacation.  I think my roommate may have over-watered my plant.  I came home to find a foul, bleach type odor coming from my plant and white mold in the soil.  (The soil on top is dry but underneath the soil is slimy.)  Also, the leaves started wilting and then turned yellow and dried out from the bottom up.  What can I do to save my tomato plant?

Answer
Hi Martina, You may have more than one problem.  If  the container is draining properly and you control the water, the soil should dry.  If it's staying too wet, too long after watering, you may need to replant it using a soil that drains faster.  The mold is not necessarily bad, just rake the soil surface every few days so you don't see it.
Fungus grows on decomposing organic material, so it's common in containers.  The leaves yellowing from the bottom may be Early Blight. It's a fungal disease quite common on tomatoes.  You'll need to spray with a fungicide labeled for tomatoes, check with your local garden center for one approved for use where you live.
Whether it survives or not...hard to tell. If root rot has damaged a lot of roots, it may struggle or die so you may need to start with a new plant.  Jim