Topiary--the art of shaping living trees and plants--usually requires building a structural frame of strong wire and growing a shrub to fit. As foliage fills the framework, careful pruning prompts the plant to fill out the desired shape. Untrained trees and shrubs won't thrive in just any cut shape, since trimming back a limb too far kills the branch. Few trees naturally adapt to the spiral shape, but one common landscaping evergreen does provide the dense canopy and whorled branches needed for this beautiful geometric form.
Step back and study the spruce for a few moments. Spruce trees grow with branch clusters evenly spaced on the trunk. Each individual cluster contains many branches growing on the trunk in a slight clockwise rising spiral. The pattern shows faintly in the foliage. Working with that natural pattern gives the best final effect.
Start cutting at the lower left side of the tree. Establish the pattern by removing only a few branches along the plane of the spiral. Keep the angle low, a rise of about twenty degrees. If the diameter of the base of the canopy is 3 feet, the right side of the line should be about 8 inches above the starting point at the left.
Move around the tree, marking the spiral by trimming out small branches along its path. End the spiral about 8 inches below the top of the bush.
Connect the gaps. Remember that pruning creates the gap between the spiral turns. Results will look ragged at first. Shaping the foliage comes last.
Prune out enough foliage to form a gap two to three inches wide between the turns of the spiral. Shape the edges of the turns for a rounded and even look. Clip needles and branch tips only slightly, since conifers put on new growth at the ends of twigs. Cutting back too far stops the foliage from renewing itself.
Clean up the interior of the tree by pruning out unsightly dead growth. Opening up the canopy exposes many dead twigs and dead branches normally hidden from view. Clip the dead growth back to its base.