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.
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