If epsom salts is all you put in it, go for it!

I actually buy it just to put around my plants. Go easy, since it's in liquid form and the plants will absorb it a lot faster than if it had to *rain in*.

You may not notice that it helps, since it's late in the season. But try that next spring and summer. All my plants seemed to shrug off pests and disease better, and absorb what fertilizer they got.

IF you have chlorine or other chemicals in it, do not use on plants. A little may not hurt them, but better safe than sorry. Some places probably have rules about how to drain waste water like that (pools and spas) but I just drain the pool onto the lawn. Doesn't hurt the grass, as I only use chlorine and drain it slow, spreading it around.