Nothing feels better in the winter than being able to garden indoors in the warm sun of a south facing greenhouse. Trees planted along the south wall of a greenhouse or sun room can give unwanted shade in the winter.

For that reason, large ever green trees (for example: Arizona Cypress, Italian Stone Pine, Eldarica Pine or oak trees), are not usually planted close to a greenhouse on the south side. The distance to plant a large evergreen tree from a south facing window can be found using this formula: tree height multiplied by 1.65 = distance. For example, an Arizona Cypress expected to grow 40 feet tall can be planted 66 feet from the south facing window (40 X 1.65 = 66 feet).

If we already have evergreen trees growing close to the south side of a sun room, we can selectively prune certain branches to allow winter sun in while maintaining the branches that provide summer shade. To do this we need to take advantage of the fact that the relative height of the sun above the horizon at noon on any day changes from winter to summer.

In Cochise County (and all locations 32 degrees north latitude), the sun is almost overhead at noon on June 21 (the longest day of the year), being 82 degrees above the horizon. This is the sun's highest position all year. The lowest sun of the year is on the shortest day - December 21 when the sun is 35 degrees above the horizon.

To use this knowledge to modify a tree too close to a south facing room, draw out the south wall and the tree. We don't have to be good artists to do this as we are only concerned with size of the window and distance from the tree. From a point at the top of the south facing window draw a line through the tree 35 degrees above the horizon (line A in the illustration). See illustration below.

Now draw a line from the bottom of the window 35 degrees above the horizon (line B).

Any tree branches that lie between lines A and B will be blocking the sun at noon on December 21 and can be lightly marked with spray paint. Prune most of the branches in this area back to the trunk, maintaining the overall symmetry of the tree.

Repeat this process using 54 degrees above die horizon. Label the upper line C and lower line D. Any branches that lie between C and D will be blocking the sun at noon on September 21 and March 22. Remove fewer branches from this area.

When finished, we will have selectively pruned the branches back to the trunk between C and B (the light and dark shading in the illustration), allowing winter sun into the south facing window from September 21 through the middle of winter until March 22.

Leave all branches above line C to provide summer shade for the window from March 22 until September 21. (A roof overhang can provide the same function.) Branches below line B will not provide shade for the window but will shade outdoor sitting areas, and should not be removed.

Dead branches and suckers can be pruned at any time. Evergreens are normally pruned in the spring and summer. When pruning, remove a few branches at a time. Don't scalp the tree. Remember, branches don't re-grow. If you need help pruning large branches, contact a professional.