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Low-E windows and houseplants

Q: We recently installed insulated, low-E, argon-filled windows in our home. I know they block damaging ultraviolet rays, but will they affect the growth and health of my houseplants?

Bunny Weisendanger, Freeport, IL

Unless they are color tinted, low-E windows allow enough light through to support plant growth. Unless they are color tinted, low-E windows allow enough light through to support plant growth. Photo/Illustration: Allison Starcher

A: Margaret McMahon, associate professor of horticulture at The Ohio State University in Columbus, Ohio, replies: The effect low-E (emissivity), argon-filled windows have on houseplants depends on how much active photosynthetic red and blue light is getting through. Most windows of this type do not remove enough spectral light (red, orange, yellow, green, blue, indigo, and violet light that combines to form visible light) to be noticed visibly by people or photosynthetically by plants. Clear, gray, and silver-colored windows are neutrally selective, meaning that all the colors are similarly reduced in the spectrum and the visible light appears dimmer. In most cases, low-E windows will let sufficient light through to support any plants situated nearby.

Colored coatings on windows are another concern when it comes to plant health since they may selectively remove photosynthetically active light (red and blue). For example, a green-colored window will remove some of the blue and most, if not all, of the red light, leading to the decline of an indoor plant. Furthermore, a blue-tinted window will remove most of the red light, while a red-tinted window removes most of the blue light, both of which could reduce photo­synthesis to a detrimental level.

In most cases, a colored tint should not affect plant growth. If, however, the light shining through appears to be dramatically reduced, there are two things you can do. First, consider only growing foliage plants that are tolerant of low-light conditions. Other­­wise, think about providing your plants with a supplemental, artificial light source, such as fluorescent or high-intensity discharge bulbs. Incan­descent light is not recommended for plant growth.

From Fine Gardening 94, pp. 80