A picture would help. Do they need water every 4-6 days? Or might they need it more or less often? What strength are you using the fert and is it every time you water?

tj

Sounds like it's rotting.

I guess I presumed that since they were mint they would tolerate wet feet, I could be over watering. The greenhouse gets really warm so I try to not let things dry out.

I use a hose end sprayer to apply the MG

I have separated the healthy looking mint and moved to a shadier spot in the GH. I will water less but opinions are still invited.

[IMG]http://i698.photobucket.com/albums/vv345/Bonaro/misc/IMG_3090Large.jpg[/IMG]
[IMG]http://i698.photobucket.com/albums/vv345/Bonaro/misc/IMG_3092Large.jpg[/IMG]

Not that those pix are helpful, but likely way too wet esp if those are solid trays on a watering bench. Stick your moisture meter in there and see what it sez.

Dan

Classic damping off -- too much water.

Shallow containers have very poor drainage. Must have extremely porous planting mix for such containers.

OP said "I have separated the healthy looking mint"
If from the same flats as in the pictures, you very likely moved the disease organisms with them.

You may need to start over with clean containers and clean propagation stock. Then plant into the ground as soon as possible. If needed, protect on site until well rotted into the soil.

Oops! I meant "well rooted into the soil!" (I imagine you figured that out.) :)