I can't tell you what the black spots are, but, most mints are zone 5 and up hardy, so I do think that mint will spread in mostly shade in zone5 and up ( including zo ne 6 Pa) so I am GUESSING it should do fine and spread very generously. I am in zone 6a SW Pa Fayette county. I will likely try this plant myself.

i had the same thing happen to my mint i took some cuttings off the plant and rooted them. That si my advice as my original mint died about a month later.. Not sure what is actually was though.

Suz, most mints grow so good they can be like a plague in a small area. Not sure on the spots, likely nothing serious, but, I really thought I should tell you that they may take over your yard if you don't confine them/it. I planted Chocolate mint in a raised bed, and it is quite robust to say the least. I am not kidding, confine the monster while you still can!

We love growing mint in a container but not in the ground. It will grow uncontrollably.

I have sometimes seen box elder beetles ( I think that is what they are) on my mint and wherever the beetles are, I see a black spots / discoloration on the leaves. Usually in June and then the beetles disappear.

Mint grows so vigorously though, that I can easily find enough sprigs that are not affected.

The owner of the house I live in planted mint in the ground and is very invasive, and drew wasps when it flowered and I cant get rid of it. I'd either dig it up and put it in a container, or take a flame thrower to it...probably the later!

If the black spots are on the underside with a corresponding yellow splotch on the top of the leaves, suspect rust, a fungal infection. Destroy infected mint plant. Prevent mint rust by watering the plant at soil level and providing good air circulation around and within it. If the "gift" was not a nursery bought plant then most likely the original owner has the same problem and you may not want to get anymore plants from them. Is there a reason you planted it so close to the downspout? Water splashing out of the downspout could also have been the cause. I agree with the others, mint is best planted in a container. Don't worry if it dries out because mint is an herb and herbs prefer to dry out between watering...once the roots have established.