i just trimmed a bottom branch on my weeping Japanese Maple. In doing so, I accidentally nicked the bark (approx 8mm x 3mm) on the trunk above the cut. I realize that Japanese maples are sensitive. Is there something I should put on the exposed part of the trunk?
In my view, this is not a good time to be pruning because there is very little metabolic activity. Otherwise, the tree will protect itself by the process of compartmentalization (search CODIT, if you want to know more). What happened is likely not a big deal - not to worry. Wrapping the damaged bark with polyethylene, however, will accelerate natural replacement of the bark if applied within 24 hours (less if rH is low) of its occurrence. Polyethylene is a barrier to water but transmits oxygen. It is readily available in a variety of forms ranging from green gardener's tape to huge sheets of visqueen. When active, some residual cambium cells are left on the xylem (wood); kept moist, they will quickly regenerate all the missing tissues across the wound and will have re-established enough bark within 10 to 15 days that the covering can be removed (it is no longer doing anything for the tree). Otherwise, closure of new bark over the wound will only come over a much longer time by growth only at the margins of the wound (just like 'healing' over a branch pruning wound occurs). If you have a small branch or two to spare, next spring peel off a long strip of bark or even a ring several inches long completely around it and promptly wrap it in poly for 15 days. Do the same with the other, but don't wrap it. I think they might be worth keeping until the end of the season just to clearly see the difference. You may want to keep the one that was covered, but I am certain that you will not like the aesthetics of the stem that wasn't.
