Light, sunlight, temperature, humidity, soil, and other cultural factors are necessarily of a general nature, because the plants with which we grow come from all parts of the world and have widely varying natural growing needs.
Daylight
Animals and humans have digestive juices and a complicated apparatus for transforming food into energy and growth. Plants have chlorophyll and roots. The roots take up food from the soil. The chlorophyll uses water, carbon dioxide from the air, and light to manufacture starch (which later becomes sugar) on which the plant lives and grows.
This is, of course, an oversimplification of a complicated botanical phenomenon. But it helps to explain the importance of light. Without it, and without enough of it, plants starve – not because of insufficient food, but because of inability to use it. This is the reason why few plants will live, and none will look lush for long, in a dark hall or on the top of a coffee table ten feet away from a window.
Intensity of light is important, and the intensity needed varies according to type of plant like for example the african violet plant. The amount needed by each type depends on the light available in its natural habitat. Consider, for example, the philodendrons, usually regarded as requiring less light than most plant groups. The vining types were first found climbing and draping trees in Central and South American jungles – but not in the dark. If you measured the light, you would find it far brighter than that in an awning-shaded window, for example.
This brings us to a frequent question – which window exposure is best for plants? There is no rule to go by. It depends, first, upon the window – its size, whether it is shaded by a tree or the house next door, and even whether it is in a city or country house, in winter or summer. In Connecticut a north-facing window in the country where air is clear, if it receives no shade of any kind, will usually provide good light for foliage plants, but little sunlight except for a short period in midsummer.
In the same situation, in summer, an eastern exposure has good light and sunlight in the morning; western, in the afternoon; and southern, the most sunlight of all. But move the window farther north, or into a sooty city; or shade it with even the high branches of a tree, and light intensity decreases. The farther south it moves, the more intense the light and the more hours it is available every day.
Always look at the lighting, intensity and period of light when placing plants indoors and outdoors.