Indoor Gardening: Supplemental Lighting

01/14/11

Sunlight. It's the number one necessity for plants. Yet, unlike water or nutrients, it is the hardest component of the plant life cycle to provide if you don't have access to the sun itself. And who has access to the sun? Yes yes, I know some of you are blessed with south facing windows or solariums or even full sun roof decks, but as an urbanite who lives in a row house, I only have east and west facing windows. And my west windows are blocked by a horrible Tree of Heaven in the evening and the tall apartment building earlier in the day: not much light for my poor plants.  There are plenty of indoor houseplants that thrive with limited light, but what about those prized plants you want to keep, even if they need full sun?

 

Indoor lighting could be your answer!

 

 

The first step to choosing indoor lighting for your plants is to understand the life cycle of your plant and how it relates to color temperature. Color temperature is measured in Kelvin (yes, that same Kelvin scale from Physics class; who didn't love absolute zero?) but don't worry, there is no math involved. The different temperatures correspond to wavelengths of light and different wavelengths simply relate what color in the spectrum the light is. Really, it's that simple!

 

"Daylight" from the sun registers around 5500K to 6500K and appears "blue" (which is why daylight or natural light bulbs have a blue cast to them). Light in this temperature is good for growing plants. However there are specifics: Most houseplants tend to be leafy and green and warmer blue light (~6500K) is excellent for stimulating this sort of growth. Think about what happens to plants when they are grown without adequate amounts of light: they stretch out and wash out. Blue light is what they are missing. This temperature controls the vegetative growth of the plant, resulting in green, lush leaves. This is where knowing the life cycle of your plant comes in handy. If your plant is happy growing new leaves, then this is the best choice of light temperature for you.

 

Some plant life cycles are different. If your plant is one who wants to flower and produce fruits, it needs the cooler temperature light in the red spectrum - about 2700K - to do this.

 

Check out this graph from Home Harvest

 

Is that enough science for you? Let me make it even easier:

 

If you have a leafy indoor plant, say a Fiddle Leaf Fig or Palm, one that is not kept for it's flowers, you can supplement its light with a warmer blue light. If you have a plant that is known for its flowering, maybe an oleander or a citrus tree for the very daring, you are going to need both red (for flower production) and blue (for leaf production) light.

 

Here are some of the different growing bulb options out there:

  • Fluorescent
    • Fluorescent bulbs now come in two forms: the tube you all know and love from office buildings and aquarium lids and the newer compact fluorescent (CFL). Both have positive and negatives. Tubes require certain housing fixtures, so they are not as simple as plugging in a light. CFLs fit in most lightbulb sockets, but their small size requires reflectors to bounce more of the light to the plants. CFLs are available in both the 3000K ad 6500K temperatures, though, so you can taylor your light for your plants needs. Both options burn cool, so they are not a risk for heat damaging your plants (unless the plant is physically resting on the bulb - don't let that happen). This is a very cheap option, making it a good investment for those who aren't sure of their green thumb skills.
  • Metal Halide
    • This option emits light in the 2700K to 5500K range. This is good for flowering and fruit production and provides the necessary light for vegetative growth. This is the closest to natural sunlight option, making for very healthy plants. 
  • High Pressure Sodium (HPS)
    • If you've ever driven past an industrial complex after dark and seen the orange glow, you've seen a HPS light. These lights are used in outdoor lighting (some streetlights are orange tinted because they use these bulbs). Since they do produce reddish light (~ 2200K) these lights are great at producing flowers but provide less than perfect foliage. It doesn't mean the plant is less healthy, but the plant might be more stretched, or "leggy", than plants grown under "bluer" light.  
  • Light Emitting Diodes (LED)
    • This could be an exciting new technology for grow lights. LEDs require very minimal energy inputs which means less of a cost on your electric bill. LEDs also can be chosen based on what light spectrum you are looking to add. 
  • Incandescent
    • In the past I experimented with incandescent "grow" bulbs with very limited success. These bulbs are hot which can scorch plants, burn out quickly, and generally don't do a good job. I suspect the blue light is more a factor of the tint of the glass than the actual wavelentgth/temperature of the light it is emitting, which doesn't actually provide any benefit to your plant.

 

Hopefully this little introduction has given you the information you need to walk down the bulb aisle at your local hardware store!  For even more information, check out The University of Missouri Extension.