Q. The shrubs growing on the southwest corner of my house are considerably larger and have more aggressive growth than the same kind of shrubs growing on the northeast corner. Is there some reason for the difference?
A. It may be as simple as the difference in light each group of plants receives. Phototropism is directional growth, particularly in plants, in which the direction of growth is determined by the direction of the light source. Most plant shoots exhibit positive phototropism — growth toward a light source, while roots usually exhibit negative phototropism — growth away from light. Some vine shoot tips actually exhibit negative phototropism, which allows them to grow toward dark, solid objects and climb them.
When plants are grown in insufficient light, either in partial or complete absence of light, they have smaller and fewer leaves, and a pale yellow color. This is due to a lack of chlorophyll. The plant’s increase in height helps it to reach a possible source of light faster.
If a plant is placed in a position of unequal lighting, the cells on the shadier side elongate faster than those on the illuminated side, and the plant bends toward the light. That is why nursery stakes should be removed immediately after planting a tree and permanent stakes installed because the cells of the bark next to the nursery stake elongate.
Plants growing near the southwest corner of buildings get considerably more sunlight than plants growing near the northeast corner of buildings. Heat is also greater in a sunnier location and cooler in the shade. Plant sun- and heat-loving plants near the southwest and shade- and heat-sensitive plants near the northeast.