i'm having trouble with my indoor peppermint plant. it has some dark black spots on it. I thought it was spider mites for a while but i used a magnifying glass to check and didn't see any. also i read that peppermint is a natural deterant to spiders. could this be blight and if so how do i get rid of it? i've transplanted the plant into a larger pot with a compost mix for vegetables and herbs. also am looking into buying a humidifier for the apartment. the plant shares the pot with some oregano. any suggestions?