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Light exposure

sun exposture diagram
See: large image of sun exposure diagram

Note how many hours of direct sun the planting site receives in the summer (see figure on right). Remember to account for the seasonal change in the sun angle when evaluating sites in other seasons.

Trees requiring full sun need at least six hours of direct sun, but all-day sun often produces the best form and growth. Trees suited for full sun to partial sun/partial shade will be adapted to a site receiving three to six hours of direct sun. Shade loving trees are adapted to sites with filtered sun or filtered shade, or those receiving less than three hours of direct sun. Most large trees grow best in full sun. Some small trees grow best in sites receiving shade for part of the day.

Some planting sites in highly urbanized areas are close to tall buildings that have reflective surfaces such as glass. Sunlight reflected from glass, or a white wall increases the heat load on a tree planted near a building. Even though the site might receive less than full sun due to shadows cast by buildings, the plant must tolerate a high heat load during the sunny part of the day. Therefore, drought tolerant trees that grow in full sun and partial shade are best suited for this site.

In addition, providing a large area of soil for roots to explore often helps trees withstand reflected light by providing more soil from which to absorb water. Leaves on trees receiving reflected light in a restricted soil area often turn brown along the edges in summer (called marginal leaf scorch) unless provided with ample water.