Strange Spots on Lemon Balm
Hi everyone, I bought a lemon balm (Melissa officinalis) from Home Depot a few weeks ago and planted it in a sub-irrigated planter that I made out of some recycled materials. It's planted in a 50/50 coir/perlite mix. It's position gets a pretty good amount of sun (I'd say it qualifies as "full sun" or pretty near that amount).
Anyway, I've noticed some black/grey blotches that have been showing up on the leaves. I've been removing the blotchy leaves as they pop up, but it seems as though the plant's growth is stunted. I was watering it almost every day, but stopped when we had about a week of rain.
Additionally, I've stopped watering it the last two days or so (the bottom few inches of the container still have moisture) in case it is a fungus. I've also noticed that the undersides of about half the leaves are a very light, pale brown, but still relatively see-through (light can still filter through it) and some of the blotched leaves are slightly brittle and dry.
It didn't really look like any of the pictures of fungal infections I've experienced before or any of the ones shown in my books. Does anyone know if this is a fungal infection, a weird bruising or a nutrient issue or something?
Thanks so much in advance.
Here is a link that might be useful: picture of blotches