While walking through our greenbelt this morning, I came across a home that has done some yard work in the last couple of weeks. This particular update is fairly common, and one of the worst things you can do when it comes to the health of your trees:
Creating a raised bed around an established tree will likely choke the tree and kill it.
When a tree is planted, it is important to put it at the proper depth. There is a point where the roots meet the trunk - this is sometimes called a Crown, or as I refer to it, a Collar. To me, the name Collar makes better sense simply because if you bury the Collar, you will Choke your tree and it will die. That's how important the depth is.
Here's a small picture from TreeHelp.com that shows you the proper depth to plant a tree and how the Crown/Collar should be slightly above the ground:
When you go to an established tree that was most likely planted at the proper depth, and add six to ten inches of bricks around it, and at least that much in soil and mulch inside the bricks, you might be making it look nice, but it will be interesting to see it come Spring time. This tree is likely bearing its last batch of fruit.
A better use of your time and budget if you are preparing your home for sale is to go out to the tree with your gardening instruments, and loosen the existing mulch. I use the "Garden Weasel" at our house, but you could use a garden rake or a small shovel. Once it's loosened up, you can sprinkle some fresh mulch over the top and the bed will look as good as new. No need for bricks or bags and bags of mulch. I also recommend Spike style tree fertilizer at this point to give the leaves a little extra green. In Texas, many trees don't loose their leaves until January or February, so keeping them green is important.
For more information on how deep a tree should be planted, visit: http://www.treehelp.com/howto/howto-plant-a-tree.asp