In the Master Gardener level 1 course there is discussion on plant growth and development, which runs the gamut of topics. I wanted to touch on one portion of that specific lecture and talk about light requirements of plants and apply it to many of us that have indoor house plants.
Plants need light for photosynthesis, which is one of the lessons that all of us picked up in high school, if not younger. Photosynthesis is the process wherein a plant converts light, oxygen and water into carbohydrates or energy. This energy is required by a plant to grow, bloom and produce seed. Without adequate light, carbohydrates cannot be manufactured, the energy reserves are depleted and plants die.When talking about light requirements of house plants, we are talking about three different things, light intensity, light duration and light quality. Light intensity is the brightness of light, measured in foot-candles. Foot-candle are the amount of light received by a 1-square-foot surface located one foot away from a light source equal to one candle. Light duration is the number of hours of light per 24-hour period. Light quality is the wavelength or color of light. Plants use red and blue light primarily, with red light encouraging budding and blue light promoting foliage growth. Most plants are green because they don’t absorb light in the green spectrum, so they reflect it back out.
Of course, our house plants come in all varieties, and that includes how much light they like. Low-light plants, those that need light at 10-15 watts or 50-250 foot-candles, would be suitable for a north window or a fairly dark corner. Examples could include plants that don’t dry out quickly such peace lilies, some begonias and Anthurium. Medium-light plants are those that require 15-20 watts or 250 - 1,000 foot-candles. Medium light areas are well-lit areas in the home, such as windows that face east. A medium-light plant can also be located near a west-facing window, but out of direct light. Examples of these type of plants include African violets, other begonias and Christmas cactus. High-light plants are those that need light at greater than 20 watts or more than 1,000 foot-candles. These do best near or in south or south-west facing windows. Examples of these plants include poinsettias, ficus, and yuccas. It is important to note that while a plant may tolerate lower light growing conditions, more light may be required to promote dense foliage and flowering.Please let your local county Extension office know if you have any questions regarding light requirements for houseplants.