Daylight saving time is on hiatus, the gardening season has drawn to a close and the long shadows of winter will soon be here. It seems like a good time to turn our attention to the light needs of indoor plants.
Most indoor plants hail from the tropics, making their ideal growing conditions far different from what we offer in our typical homes. Thin new leaves, loss of lots of older foliage and limbs stretching towards a window can all be signs that your plant is craving more light. Without adequate light plants are unable to store energy for growth.
Indoor light is more subtle than the light in our gardens, which can make it trickier to assess. For more precision, a photographer’s light meter or a simple light meter app on your phone will measure the light in foot-candles or LUX units. Horticulturists use foot-candles, so if you have a device which gives a LUX reading, search the web for an easy LUX to foot-candle calculator.
In general, growers characterize plants as needing high, medium or low light. Here are some guidelines to help assess the type of light in your environment with greater accuracy.
High Intensity Light
- 1,000+ foot-candles
- 4-6 hours of sun per day
- Crisp shadows and dark contrast at the brightest time of day
- Within 2’ of east facing windows
- Within 2’ of south-facing windows (October-March)
Medium Intensity Light
- 500+-1,000 foot-candles
- Within 2’ of north facing windows (April-September)
- 2-6’ from an east or west-facing window
- 1’ to the side of an east or west-facing window
- Approximately 10-14 hours per day of fluorescent office light
Low Intensity Light
- 50-500 foot-candles
- Faint shadows at the brightest time of day
- Within 2’ of north facing windows (October-March)
- 6-10’ from south-facing windows (April – September)
- Few plants survive in fewer than 50 candles
Knowing the light intensity will help determine the best placement of plants and select plants which will thrive. Variables such as humidity, drafts and temperature also factor into a plant’s health, so be sure to take this into consideration, too. As always, knowledge and keen observation skills are key to successful plant care.
Additional information on plants and light:
Written by Linda McDonnell, a Denver County Master Gardener