Light and Plants
Of all an indoor plant’s needs, none is more important to health and
long life than the amount of light it receives. Light is the power source
for the process of photosynthesis, by which the leaves produce sugars and
starches to feed all parts of the plant.
The amount of natural daylight that enters a home through its windows is
only a small fraction of the light outdoors under an open sky. Outdoors,
the summer sun at midday may produce as much as 10,000 or 12,000 foot-candles
of light (a foot-candle being the amount of light cast by a candle on a surface
1 foot away). Inside a house, however, plants in a sunny window may receive
only 4,000 or 5,000 foot-candles, and a few feet from the window the level
may drop to 200 foot-candles or less. Still farther away the average light
may range between 10 and 100 foot-candles (a book can be read comfortably
in illumination of 50 foot-candles or less). Fortunately for gardeners, many
tropical plants tolerate low light levels or they could not be grown indoors
at all.
Within these low levels, the light needs of different plants vary. The
plants generally are divided by light levels into the following three broad
plant categories:
High Light
This group includes plants such as Croton, Ficus, and Hoya, which require
full sun at a south-facing window or bright light reflected off a light-colored
wall.
Medium Light
This category belongs to the intermediate plants, such as Rex Begonias, Dracaenas
and Ivy, that thrive in partial shade or the filtered light coming through
a sheer curtain.
Low Light
These are plants that get along on a minimum of illumination, such as Calatheas,
Fittonias and many Ferns, that can survive in indirect, shadowless light
coming through a north-facing window.
Since most plant owners want their plants to be beautiful, yet not grow
too quickly out of bounds, the light level recommended for each species in
our variety section is the least that will maintain health without encouraging
fast growth. Window light is generally one-directional and causes the part
of the plant away from the light to stretch toward it; if you want a plant
near a window to grow evenly, give it a quarter turn every day—or at
least every time you water—so
that all parts of the foliage will get equal light.
It is fairly simple to tell whether a plant is getting the right amount
of light in the location where you have placed it.
If the distance between the new leaves on its stems is greater than the
distance between the older ones, the plant is stretching to get more light.
Its stems indicate this by elongating, in some instances bending, toward
the light source. In such a case, move the plant to a spot where it will
get more light.
If the plant wilts during the hot part of the day, and the leaves begin
to develop yellow and then brown patches, the plant is getting too much light.
Move it back from the window or draw the curtains during the middle of the
day. Another symptom of too much light is when the leaves start growing vertically
as to “hide” from
the sun by lessening surface area exposed to sun.
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