Corsican Mint dying
I am trying to propagate Corcisan Mint in the greenhouse and have several flats growing like mad. I water deeply every 4-6 days and finish with a shot of miracle grow. There is no chance of frost and I see no rust or powder.
My mint looks like it is frost damaged. Starting at one corner of the flat it is turning brown/black and dying off and its spreading.
What is going on and how do I stop it?