March 26, 2009 in Washington Voices

Time to get seeds under the lights

Pat Munts Correspondent

We are only six weeks away from our supposed last frost date of May 15.

For many gardeners that means it’s time to start vegetable and flower seeds indoors. There’s lots of information out there about how to start seeds. But often overlooked is how to provide the artificial sunshine that makes your seedlings grow.

Plants use different parts of the light spectrum during their growth cycles. Seedlings do better under the blue part of the spectrum, while those at the flowering stage need warmer reds and oranges.

Fluorescent lights are probably the most flexible light source for the home seed starter. They put out twice the light of an incandescent light and remain cool. A bank of two or three 4-foot-long shop light fixtures suspended on chains from a frame or shelf provide lots of light and can be easily moved up and down to accommodate the height of the plants without cooking them.

The choice then comes down to what type of bulbs to put in the fixtures. Fluorescent lights now come in almost any mix of the color spectrum so finding the right spectrum and intensity of tube for your needs isn’t hard. Ordinary inexpensive fluorescent tubes come in a wide range of warm and cool colors and will work as grow lights. The bulbs have a life of about 20,000 hours but need to be changed every year to maintain their intensity. Tubes sold as “grow lights” have a better color spectrum balance than standard fixtures but are often much more expensive.

High-output fluorescent lights are much smaller than standard fluorescent fixtures, but put out twice the light. More light means better growth for the plants. High-output systems are much thinner than standard fixtures, making them useful in tight spaces. The tubes have half the life of the standard tubes and are much more expensive.

Commercial growers often use high-pressure sodium or metal halide lights because they put out several times the amount of light that other growing lights do. Plants grown under them will look like those grown in natural sunlight. There are home-sized lights, but they are expensive, and the high-pressure sodium lights can generate a lot of heat that can affect the plants.

Put growing lights on a timer. Even with good lights, seedlings benefit from strong light for up to 16 hours a day. This means that even sunny window sills need to be lit because our natural 12-hour days we get this time of year don’t have enough light. Throw in dark, cloudy days and natural sunlight just isn’t enough to grow strong, stout seedlings.

Suspend lights on chains so that they can be moved up and down. Because light intensity decreases rapidly the farther a plant is from the source, growing lights need to be within 3 inches of the tops of the plants to be effective. As the plants grow, the chains can be shortened to keep the lights in place.

Pat Munts is a Master Gardener who has gardened the same acre in Spokane Valley for 30 years. She can be reached at

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