Ginger Plant Rotting

I have my ginger in a greenhouse at about 70 to 75 degrees Fahrenheit. My problem is that it is rotting away. It's in a 4 inch pot about 1/8 inch below the soilless medium with 14-14-14 Osmocote. The pH is 5.0 to 5.5 I water very little so what do I do.
P.S do you know of a better soilless mix I can use for my plants. I'm talking herbs.

Ginger should do well in the Pro-mix type media. It has a growing period and then it dies down and rests. I presume you watered it while it was trying to rest and so it started to rot. Keep the rhizome at the surface so that light can get to it. Dry it out now and cut any rotted areas away. In May or June it should start to sprout again when you can replant it-only the bottom half buried-and give it lots of light and hope!