The Q&A Archives: Light Definition

Question: Are you ready for the bonehead question of the day? I would like to know the basics of lighting for all kind of plants whether house or outdoor. What do they mean when they say bright indirect light? (isn't that redundant?) What is the difference between northern light and southern light? Is there a certain amount of light per day that determines how it is categorized? I am completely confused... I don't know how I can sleep at night! ;-)

Answer: Well, we'd like to simplify things for you, but the following are guidelines only, and your mileage may vary. Indoor plants fall into one of five basic categories in terms of light requirements. They are: 1) Full sun, which is defined as an area with as much light as possible, within 2 feet of a south-facing window. This suits desert cacti, succulents and pelargonium. 2) Some direct sun, defined as a brightly lit area with some sunlight falling on the leaves during the day. Examples are a west-facing or east-facing windowsill, a spot close to, but no more than 2 feet away from an unobstructed window. This is ideal for most flowering houseplants. 3) Bright but sunless, an area close to but not in the zone lit by direct sunlight. Many plants will grow well in this area, which generally extend for about 5 feet around a window which is sunlit for part of the day. A large sunless windowsill may provide similar conditions. 4) Semi-shade. This is a moderately lit area, within 5-8 feet of a sunlit window, or close to a sunless window. Only a few flowering plants will grow here, but it's suitable for many foliage houseplants. 5) Shade. Defined as a poorly lit area, but bright enough to allow you to read a newspaper during several hours of the day. No flowering plants will grow here, but many foliage plants, such as Aglaonema, Aspidistra and Asplenium, will grow here. In terms of outdoor plants, exposure to full sun or full shade are self-explanatory, but there are many degrees of shade, for instance, 'dappled', caused by overhanging branches and foliage, or 'deep', caused by obstruction such as a wall or building, and many variations in between. If a plant needs full sunshine, plant it where it will receive 8-10 hours of direct summertime sunshine. Roses and tomatoes fall into this category. 'Part sun' could mean either morning sun and afternoon shade, or afternoon sun and morning shade. 'Part shade' usually means protection from hot afternoon sun but exposure to early morning sun. The difference between northern light and southern light is the intensity and duration. South and west exposures are the most intense, north and east are slightly lower on the scale, but can provide bright enough light to keep many plants growing. Each garden is unique and many plants that reportedly don't like certain exposures may very well thrive in a garden when they shouldn't. Use the guidelines on the plant tags or in the catalog descriptions to help your place your plants in the garden so they'll receive the right exposure. Hope this clears some of the confusion!

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