I planted some herbs in pots without proper drain holes. When I noticed them dying, it took me a while to figure out the reason. It turns out that the soil had gotten waterlogged and rotten. I repotted the herbs in new, good soil, this time with proper drainage, and although it is too early to be sure, it looks like some of them will recover. But the old soil smelled so foul as I dumped it out of the pot, I knew beyond any doubt that was what was killing the plants. I now have it in an open container, out of the weather, so it can dry out. My question is, after it is dry, can it be rehabilitated and put back into use, or is it a loss?
The bad smell is caused by the soil going anaerobic when it was waterlogged. It's most likely caused by bacteria. When it dries out these anaerobic bacteria die, or go inactive, and the smell disappears. After that you can use it again.
Most herbs do well when given a good watering and then allowed to dry out quite a bit between waterings.
One great way to protect the drain hole with clay pots, is to use old broken pot shards, curved side up over the drain hole, followed by some course material and then the soil. That way it takes a long time for fine material to clog the hole. It also helps if the pot is raised a little bit on pebbles or some other material if it's sitting on something flat, like concrete. A pot sitting flat on a hard surface will lose drainage very quickly.
As Rene said, the odor is from anaerobic conditions and when it dries out those bacteria will go dormant (add some mycelium to get rid of the anaerobic bacteria).
Before you reuse that now dried out soil give it a boost of microorganisms by adding it to a compost heap, then you will have some bioactive soil already mixed with organic matter to use.
Dale brought up the right way to put plants in pots (containers) good drainage is key to healthy plants and soils.
At any given time I’ve got an open soil mixing tub (or more than one) for use in potting up new plants. It’s got whatever I’m using for my current soil mix in it, and that’s where I keep handy any amendments I may have on hand to mix in, or garage-sale bags of commercial potting soil. I bring all my old spent pots and containers back to this location and add them in as well, throwing out any roots and stems that are too large in the process. (They go in the bottom of larger pots later.) I often have an anaerobic pot that I put in water in a failed effort at revival and then forgot about; it goes in the mix with no harm.
I guess what I’m saying is, it’s fine, but the way I would use it is to mix it with other soil; I wouldn’t plant back into it unmixed.