As the days get shorter, and the gardens, trees and lawns go dormant, most gardeners turn their attention to their indoor houseplants to get their daily fix of greenery and natural color. It’s important to remember, however, that your plants are missing the sun even more than you are. Lack of the right kind and amount of light is one of the main causes of slow-growing, sickly plants in the home. Even in the summer, unless your houseplants have prime spots in a big southern facing window, they could benefit from some sort of supplemental indoor light.
Unfortunately, it’s not as simple as setting your sun-deprived potted plant under the nearest bright reading lamp. It’s not just any light that plants need—color and intensity matter too. Light, which we see as white, is made up of a rainbow of different colors (or wavelengths). Photosynthesis, the process by which plants turn light waves into food, relies mainly on red and blue wavelengths and uses very little of the yellow or green. Natural sunlight is a full spectrum light, meaning it contains all the different colors and plenty of the red and blue that plants need to thrive.
Choosing the Right Light Bulb
Choosing the right light bulb for your indoor plants means trying to get as close to full spectrum natural sunlight as is practical and economical. The home gardener has four choices:
Standard light bulbs are better than no supplemental light for your plants—but not much better. Though they emit plenty of red light, which plants need to flower and fruit, they are short on blue light, which fuels healthy stem and leaf growth. Incandescent bulbs run hot as well, which makes it difficult to get them close enough to your plants to do much good. And finally, they are energy inefficient and more expensive, burning out more quickly than florescent or LED alternatives.
Florescent lights have long been a favorite of home gardeners taking care of houseplants or starting seeds indoors — and with good reason. There are many plant lighting fixtures available that take florescent lights or it’s easy to build your own. They are cheaper than incandescent lights, cooler (so they won’t burn your plants) and last longer. And full spectrum florescent lights are readily available (sometimes also called “florescent grow lights”), so you don’t have to worry about your plants missing out on the red and blue wavelengths they need.
When buying florescent bulbs, look for T5 bulbs (the “5” is a measure of the tube diameter) rather than T12, which are better suited for lighting offices than flora. The smaller the tube diameter, the more intense the light emitted, and if you can find T5 bulbs with an “HO” (for “high output”) rating, all the better.
LED lights are even more energy efficient, and thus less expensive, than florescent lights. They also don’t run hot like incandescent lights do. LED technology allows the lights to be carefully customized, so look for products advertised as “horticultural” or “grow” lights to make sure they are designed to give off adequate blue and red wavelengths. Lights so designated will also shine at the right intensity for your plants.
Commercial growing operations often use high intensity (gas) discharge lights in their growing operations. They are long lasting and efficient but need bulky and expensive fixtures and thus are rarely found in homes.
Except for HID lights, any fixture can be used to hold your grow lights, if you make sure that fixture is marked as appropriate for the type, size and energy output of the bulbs you buy. You can use anything from:
- A desktop or sconce LED grow light.
- An arched floor lamp with a grow bulb.
- A DIY system made of a couple of florescent bulbs in basic metal fixtures hung from metal chains (a long-time favorite of indoor seed starters).
For many years, it was difficult to find attractive and affordable plant light systems for the home, especially ones using LED bulbs. But with the booming popularity of indoor gardening, every day there are more options for those looking to light their indoor plants without breaking the budget or making their living space look like a commercial greenhouse.
Plant Lighting Tips
- Most supplemental plant lighting should be placed 6-12 inches from the light source.
- Leave the lights 16-18 hours a day for plants receiving no outside light (12-14 hours a day for those that get some outside light).
- The lights should be set to shine for a stretch that includes all the daylight hours. This mimics the plants’ natural cycles and supplements the natural light they are able to get get through a window.
- Don’t leave them on all the time. Plants need some darkness each 24 hours to rest and regenerate, just like we do.
How Much Light Do Plants Need?
Different types of plants have different light needs (though most houseplants fall into a broad “medium-light” category), and light intensities are difficult to measure across types of bulbs. We are used to thinking of wattage as indicating how strong a light is, but what watts really measure is how much electricity a light bulb uses over an hour. So, in terms of brightness, a 60-watt incandescent bulb burns as brightly as a 14-watt florescent bulb and an 8.5-watt LED light.
A better gauge of light intensity is lux, a measure of brightness over a square meter, with most plants needing between 2500 and 10000 lux over their extended day. Some light bulbs and fixtures are rated in terms of lumens, and one lux equals one lumen dispersed over one square meter, so to understand how much light those shed on your plants, you also must consider how far away your light source is.
Fortunately, for the math challenged among us, most lights you will want to consider for your plants will be clearly labeled as “grow” or “horticultural” lights. Any such products will be the right range of intensity and with the right amount of red and blue wavelengths for optimum plant health.
For those interested in a more scientific approach, there are inexpensive light meters available that will calculate lux around your plants (be sure to take readings over the course of a day to capture a solid average). These meters, however, report only the intensity, and not the wavelengths, of the light around your plants. If you want to test for yourself whether they are getting enough red and blue light, you need a more expensive tool—a PAR (Photosynthetically Active Radiation) meter, which registers only the intensity of red and blue light waves.
Though the appropriate amount and type of light is vital for keeping your houseplants healthy over the winter, it is just one way to baby your indoor plants when it’s cold outside. Check here for many more winter tips for houseplants