Horticulture Principles and Practices

not uniformly lit. While plants are in the care of commercial nurseries, light conditions
are maintained at optimal or near-optimal conditions, which usually means at higher
intensities than would be found at home. For example, tropical foliage plants generally
prefer high light intensities (above 10,000 lux and in some cases even above 30,000 lux).
Chloroplasts in leaves are known to orient themselves differently to suit high- and
low-intensity light conditions. The problem with houseplants arises when they are transferred
from the greenhouse (high intensity) to the home (low intensity). This change is
drastic for many plants, which immediately begin to readjust to adapt to the home environment.
Plants readjust differently, with variable consequences in terms of their aesthetic
value. Some plant species such as Ficus benjamina and Coleus hybridus adjust to
low light levels by losing chlorophyll and subsequently dropping their leaves. These
plants develop new leaves that are much thinner and have chloroplasts that are uniformly
distributed throughout the lamina, obviously for better interception of light. Other
species including palms and lilies respond to low light levels by changing color from
green to yellowish, but without abscission. By remaining attached to the plant, these
sickly leaves reduce the aesthetic value of the plant. Some nursery owners, anticipating
the eventual transfer of plants to homes by customers, may put plants through a weaning
period to acclimatize and prepare them for the home environment.
A variety of sunlight intensities are experienced in the home, depending on the season,
architectural design of the house, and other landscape activities around the house or
even nearby houses (Figure 11–10):
1. Direct sunlight (full light). A house that has no large trees in its immediate
vicinity or structures that may block sunlight can receive 100 percent sunlight for
parts of the day through windows that face east, west, southeast, and southwest.
2. Indirect sunlight (filtered bright light). When trees obstruct the direct sunlight, it
enters the house after going through the leaves. Some windows have decorative
curtains and blinds that also filter direct sunlight, making only a portion of its
intensity (about 50 to 75 percent) available indoors.
3. Bright light. Bright light occurs near the areas where sunlight directly or
indirectly enters the house. Such areas are less bright (about 25 percent) than
the primary source.
4. Medium light. North-facing windows do not receive direct sunlight. Even
windows facing east or west do not receive direct sunlight if heavily obstructed.
FIGURE 11–10 Natural light
received in a room is influenced
by factors such as the number
and kinds of windows, the window
treatment, the presence of
trees near the windows, and the
orientation of the house.
Medium light
Poor light
N
Bright
light
Window
Sun
Trees
Curtains
Filter incoming
light
364 Chapter 11 Growing Houseplants