I know this is an old thread but want to give a HUGE thanks to those that recommended IOSSO Mold and Mildew Cleaner....
I followed the directions exactly for the first piece of chair cushions (pillow). I was probably using the wrong thing for the scrubber (Dobie pad) because that one did get a bit faded (my fault). It was also taking a long time so decided to try the soaking method....
SUCCESS!
I had even washed a few of the cushion covers that could be removed - they still had the mildew on them. Soaked them all and they look brand new.
I did find that you can't reuse the solution. I had tried soaking 2 cushion covers.....they came out great so stuck 2 more in the same (used) solution. That second try did nothing so I did a new solution....again, success!
I bought a huge plastic Storage container so I can soak the larger cushions that can't be zipped off.....will take awhile but I figure I have the rest of the winter.....
I had gotten the smaller jar to make sure it worked.....already have the larger one on order....from Amazon.