When Houseplants Receive Too Much Light*

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Most houseplants actually adapt well to full sun, as long as they get used to it gradually. Source: Claire Tourigny, from the book Les 1500 trucs du jardinier paresseux by Larry Hodgson

The truth is that more indoor plants lack light than receive too much of it. Even so-called “low-light plants” (which would be better called “low light tolerant plants”) do much better with plenty of sunshine than in a shady corner.

When damage due to excess light does occur, it’s almost always due to a plant sitting on a south or west window ledge or in a sunny greenhouse. Even then, it isn’t likely to be a problem except in late spring and summer. In temperate climates, nearly any plant can take full sun during the winter when light is naturally weaker.

Most damage blamed on excess light is actually due to overheating. With sunlight streaming through glass windows and little air circulation, heat can build up tremendously, causing injury to even sun-loving, heat-tolerant plants such as cacti and other succulents. Temperatures right next to a sunny window can reach 140˚ F (60˚ C) or higher, which is far more heat than most plants can tolerate.

Symptoms of excess light and heat include the following:

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The leaves of this Brugmansia burned with it was moved too quickly from a cool, dark basement spot to a hot, sunny window.. Source: laidbackgardener.blog

  • Wilting during the hottest hours of the day;
  • Foliage curled downward;
  • Brown spots or pale and translucent spots developing on the side of the plant exposed to the sun—referred to as burning;
  • Yellowing and thickening of new growth;
  • Excessively compact and stunted growth.

If your plant shows symptoms of excess light, use any of the following methods to decrease light intensity.

  • Move plants away from the window. The worst symptoms of excess light most often occur in plants that are almost touching the windowpane. Moving the plant just a foot (30 centimeters) away from the glass can help.
  • Move the plant to a less brightly lit location, such as in front of an east-facing or north-facing window or to either side of a south-facing or west-facing one.

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    Sheer curtains will keep the hot sun off plant leaves. Source: pinterest.ca.

  • Draw sheer curtains between your plants and the window when the sun is at its brightest—around noon and during early afternoon.
  • Plant outdoor trees or shrubs in order to shade your home’s windows during the hottest hours of the day. Use deciduous plants in temperate climates. When they lose their leaves in the autumn, they let in more light just when the plants need it most. In tropical climates, evergreens make better choices because they filter the sun year-round.
  • Put shade-tolerant plants behind other plants that can put up with the high light levels in the room.

Simple, n’est-ce pas?

*Text partly derived from the book Houseplants for Dummies by Larry Hodgson, IDG Books
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