Kind of funny story about the burnt logs. My son brought me a burnt log from his nursery as a gift of sorts. I appreciated the gesture and we sited it together and dug it in. I then invited him to go down the hill with me to a rather large burn pile from a previous land clearing project which was off in the weeds a bit. He immediately saw the potential, and told me I was sitting on a gold mine. Since then, he's been dragging random burnt 'yard art' up the hill and placing it in the yard for me. I love the look of it.
Re colonizing, I just let it sit and whatever is already there soon encompasses the logs. Depending on where they are sited, some of the moss/lichen dries up during the summer, then rejuvenates itself over the wet season. I just let it do its own thing. Same with large boulders, some will get green, others not so much. I was unaware the burnt material had any sort of antiseptic nature to it.
Along that line, I also have lots of moss in my gardens and lawn and in some trees. Again, I pretty much just let it be. If it gets over-eager, I'll pull it off newly emerging plants, but I don't get tweaky about it. I like the soft look and assume someone somewhere is likely paying good money for whatever it is I have.
This flat rock serves as a landing for my laundry basket (there is a clothes line running from the deck post up into a hemlock tree directly above the rock) and gets fairly mossy over winter, then pretty much dries up during summer. It has really pretty color to it, different than most rock we find out back.
