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Grow Light Basics

Different plants need different light intensities and while there are many houseplants that will tolerate lower light within your house, if you have more plants than windowsills or want to try starting plants from seeds, investing in grow lights may be a good idea.

Light
Plants are solar powered. All green plants use the energy of light for photosynthesis (the process of taking carbon dioxide from the air, plus water, splitting them into carbon, oxygen and hydrogen and recombining them to form sugar.  This “feeds” the plant and helps it produce leaves, flowers and fruit).  Seedlings, for example, need a lot of light and probably won’t grow well indoors in just a sunny window; they usually require grow lights.

How can you tell if your plant needs more light?  The leaves may get lighter in color (in some cases, turning yellow and dropping off), the plant may get leggy (meaning there will be more space between each leaf on the stem), the plant may have stunted growth and/or the plant will lean towards a light source.

Light intensity drops off rapidly the farther you get away from the source.  A plant that is 2 inches from the source receives far more light than a plant that is 12 inches away.  You can control the amount of light a plant receives with the brightness of the bulb (measured in lumens), the distance the plant is from the bulb, and how many hours a day you have the lights turned on.  You must use some common sense regarding distance from bulb to plant: if the bulb is giving off a lot of heat, then the bulb must be a few inches further away from the plant than if the bulb is cool.

The type of light you give your plants matters just as much as the amount.  Plants use red and blue light on the color spectrum, but not so much yellow and green.  Generally, the more red a light provides, the better for flowering and fruit production and the more blue a light provides, the better for foliage production.  Light color is measured in Kelvins; a lower Kelvin number (say 2500K) will be more red and a higher Kelvin number (say 6400K) will be more blue.  Choose a bulb with a lower number if you have an established blooming plant, but if you are starting seeds, get a bulb with a higher number.

Different Types of Bulbs
There are three most-often used types of bulbs: incandescent, fluorescent and LED.  While LEDs are the most energy efficient, they are also the most expensive.  If you are looking to invest in one, check out this selection on Amazon.  Incandescent bulbs are the cheapest, but least energy efficient and also the hottest—with an incandescent you run the risk of burning your plant.  Fluorescent bulbs are only slightly more expensive than incandescents, but will last much longer and are much cooler.  Both come in standard bulbs and in tubes.

Can you buy any old bulb from the hardware store?  Yes; just make sure to see where it falls on the color spectrum.   A combination of warm white and cool white bulbs in a 4 bulb fluorescent fixture will give you what you need to cover the blue and red ends of the spectrum, and are cool enough that you can suspend them just a few inches above your seedlings without burning.  The warm whites also make the overall light effect more pleasing to the eye.

Different Types of Fixtures
There are two main styles of fixtures: clamp lights and tube light stands.  The clamp lights are great if you just have one or two plants that need more light.  Of course, you need something to clamp it to.  The light stands are ideal for seed starting.  They’re long enough to accommodate one or two seedling trays and have a moveable light fixture that you can raise or lower depending on the height of your seedlings.  If the start-up cost of a stand fixture is too much, you can even DIY your own fixture; there are many plans available online.

Stephanie Fleming was raised at Behnke’s Nurseries in Beltsville. Her Mom, Sonja, was one of Albert & Rose Behnke’s four children. She was weeding from the moment she could walk and hiding as soon as she was old enough to run, so many weeds, so little time. Although she quickly learned how to pull out a perennial and get taken off of weed pulling duty.

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