[actives] APE, when to harvest and what about black caps.

Hello first time grower here. Very new. I have some APEs that are growing. I have read that you are supposed to harvest them when they feel like marshmallows. Is this true? Are there anything else I should look for?

Also, one has a black cap? Should I be concerned? Do I pick it? Leave it? Is there something I did that caused this and if so, do I stop?

Any and all information is welcome.