We have accidentally nicked the trunk of our Bloodgood maple. How should we repair this in order to protect our tree?
By 'nick', do you mean an area of damaged bark that is less than 3cm x 3cm? Like whis4ey said, it will repair itself, but you'll probably want to keep soil and water away from the cut to avoid the introduction of fungi and bacteria to the wound. That said, you probably just need to wait.
I agree the tree will likely be fine on its own. But if you feel you must do something... Mix equal parts manure compost, diatomaceous earth, and soft rock phosphate (wood ashes work too) and add some water to make a paste. You can also add a little liquid seaweed. Paint the wound with the mix. The manure compost and liquid seaweed feed the tree at the point of injury boosting health, the phosphate gives it immediate access to a source for building new plant material, and the diatomaceous earth kills/drives away bad bugs that might try to use the wound as a point of entry to chewing up your tree. Again, this is probably overkill but since you asked.
But blake, wouldn't this paste just be introducing all sorts of pathogens directly into the wound? (the compost in particular?)
Properly composted manure has the opposite affect - it contains antibiotics and microorganisms that kill pathogens. http://compost.tamu.edu/docs/pubs/UrbanEnvironment.pdf
