the grass I'm growing is actually wheatgrass which I use for juicing, but I figure you people on this forum would know about grasses so I will ask here

I've got tall raised bed gardens. They are 22 inches tall made of cedar.

Every time I plant a crop of grass it grows absolutely beautiful, but at some point (usually when the grass is 4 � 6 inches) after a few rains it develop some kind of slime at the very base of the plant by the soil, I'm assuming the slime develops in the root system and is climbing up. The slime eventually kills the grass

What can I do to address the situation?

I plant the grass very close together and thick. You think I should planted much thinner to give it better airflow?

maybe just drilling a whole series of holes along the base of the planter will be good enough?

Or maybe I need to take out all of the soil, lay down a layer of gravel on the bottom of the bed, put landscaping cloth on top of that, and then put my soil back on top of that. Would be a lot of work and expense but maybe that's the only way to deal with it?