Houseplants are tropicals, plants that evolved in a climate of steady year round warmth, that come from the understory of jungle-like areas. They do well with relatively low light levels. Recommendations to grow a plant in a North window has nothing to do with geography; it is a call for a cool situation and indirect light. A recommendation to keep a plant in an East or West window means it needs diffuse light all day, or direct sun half the day.
How much light do houseplants need?
But even indoors light and the heat that comes with it changes with the seasons. In hot weather, the East window is best for plants that like to be cool because afternoon sun is hotter than morning sun. A South window provides the longest hours of direct sun available which helps most flowering plants. But the closer you get to summer, the hotter the south window becomes. I handle that by moving plants that need part shade, African violets for example, back a foot or two from the window as the sun heats up. the sun’The seasonal variation is the position of the sun in the sky also affects the light your houseplants receive. Since in summer, the zenith of the sun’s trip across the sky is higher than in fall or spring, it is less likely to shine directly into a window. Especially a window with an overhang or near a tree. That protects sun-tender plants, but can rob sun-loving plants of light.
And, summer and winter, mirror and white walls bounce it and may be adding to the levels on the sill. Interior lighting also affects the plants — fluorescents, especially if they are less than a year old, add to the footcandles the plants receive. So do ordinary incandescent bulbs. African violets have flowered under my little old desk lamp.
To sum up, I find plants forgiving and wildly unpredictable in their responses to environment. A baby ficus tree I bought in a southern nursery grew up to be a ceiling high tree living in Washington, DC, in a dark corner of a room papered in Chinese red. The usual recommendation for a ficus is good light in a window facing West or East. What was different about this plant’s situation is that it spent six months of the year on a covered porch. That saves a lot of light-deprived houseplants. And also maybe that, having starting out as a baby with low light, the plant adjusted to it.
Plants will tell you right quick if they are getting enough. A ficus drops its leaves. If you improve it by adding floods, or moving it closer to a bright window, or moving it back from light that is too bright, it will stop dropping leaves. The real answer to how much light does my plant need is: consult the plant.
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