So, now that I know it can be done wrong, what's the correct way to trim a tree?
Hire a certified arborist!
That's kind a like saying take your bike to a real Honda shop mechanic. While we'd like to say that's the fix, the results may be mixed.
I had hired a certified arborist. When I first bought this property, there were several large trees that the PO had let go. The one in question had two large low branches that were reaching into the driveway and parking area and would actually hit the cars. You couldn't walk under them. If you'll note the unnatural but pretty ball shape of the tree. It was trimmed all over. Along with 4 other larger trees. He also took down a 5 foot diameter Sycamore and a lot of other work.
So when he brought the cherry picker and 6 man crew in, somebody got to those branches and did what's called a "flush cut". Cut the branch off flush with tree trunk. This leaves a really nice looking result to the untrained eye, but ultimately results in a knothole, which results in decay, an opening of the wound, infiltration of water and insects, and the death of the tree, it took about 4 years for the knotholes to appear and 4 more before i decided to do anything about it. Hired another certified arborist. He pointed out to me what had happened, and surprisingly, didn't have much to say about fixing it other than confirming what i had found on the internet: don't fill it with anything, and confirmed the drilling of drain holes.
He went on to fix some other tree problems. He was more interested in some big ticket tree removal issues I had. I took over the Maple tree. I read about covering the wound and letting it heal, made the covers.
They say when you have a medical problem, don't trust your doctor if they aren't fixing the problem. Keep shopping around and reading till you find an answer. That's what i do.
Here's some info on pruning. The proper way leaves a bump of the "collar", which is unattractive, but healthy.
http://na.fs.fed.us/spfo/pubs/howtos/ht_prune/cuts.htmClick on "next" to the page that shows the wrong way to do it. As the article says, you can't judge the efficacy of the cut until next year!
