Bricks are widely used for bordering trees and other landscaping plants, due in large part to the ease with which they can be joined to create a seamless boundary against grass and weeds. In order to fulfill this function, though, they must be mortared. Doing this on a sloped yard presents a few problems, and though these problems can be addressed, it takes quite a bit of advance planning if you are going to have any kind of permanent boundary around the tree.
Things You'll Need
Start with new trees only and lay the brick prior to planting. The problem with doing this project on established trees on a sloped yard is that much dirt would have be to dug away in the process, which can cut, break or otherwise disrupt the roots and weaken the tree. Additionally, the soil will need to be partially refilled once the brick is laid and placing layers of soil over a tree's roots can adversly affect respiration processes.
Determine the size of the circle you want to build your brick border. The smaller the circle, the lower your brick border will have to be. Use landscaping spray paint to outline the border.
Provide a leveling guide. At the highest elevation of the circle you've outlined, drive a stake into the ground. Wrap twine around the base of the stake. Then drive a stake into the lowest part of the circle. Wrap the other end of the twine around this stake, and then slide it up or down until a level gently held up to the center of the twine reads exactly even. Secure the twine in place. Your brick border will be built up to this level at the lowest level, and will wrap around to become progressively shorter until it arrives full circle at the highest point.
Create a flat surface to lay the bricks on. Use your shovel to remove the sod and any grass or vegetation present. A tamper should be used to flatten the bottom layer of soil.
Lay the bricks, neatly applying mortar between each one. Continue laying bricks until they have reached the level of the twine at the bottom. Then, level the border off all the way around.
Dig deep enough within the border to allow the root ball to sit inside without any roots being above the level of the brick border. Once the tree is set in location, use fill dirt throughout the interior of the border up to the rim.
Stake the tree using 6-foot metal stakes driven into the ground outside of the brick wall on three sides. Use wire to secure the tree to these stakes so that it does not move as the roots spread out and establish.