The Gardener Within: Joe Lamp'l, a Master Gardener and author, shares tips on providing lighting and grow light basics for plants that need to overwinter indoors..
Lots of folks bring their gardens inside over the winter months. All kinds of delicate perennials, tropicals, citrus, and even herbs and salad greens, not to mention countless new seed starts, can wait out the cold indoors if they have the right conditions.
The most important condition is light. By understanding how plants use light, and the many lighting options available today, you can put together a lighting system that’s right for the plants you want to grow indoors — or at least sustain — until they are able to venture outside again. Things to consider:
• Color. Bright sunshine contains the full spectrum of light wavelengths from red through yellow and green to blue and violet. Plants use all of these wavelengths for photosynthesis, but red and blue are two of the most important. The blue spectrum promotes vegetative growth so young plants build robust, full foliage. The red wavelengths promote flowers and fruits.
• Intensity. All plants need light to thrive, but some plants can get by on lower intensities than others. Native tropicals, shade-loving forest plants and houseplants like ivy and philodendron don’t need as much light as Mediterranean succulents or desert cactuses. Flowering plants of all kinds, such as orchids and gardenias, generally need brighter light to flower and produce fruit.
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• Duration. No matter how much light they use to grow, plants need a rest now and then, to accomplish their other functions of metabolism. Plants’ preferences for light to dark are divided into short-day, long-day and day-neutral.
Short-day plants thrive on less than 12 hours of light in a 24-hour period. Most will also need to have a stretch of even shorter days to signal them to set buds and flower. Azaleas, chrysanthemums, poinsettia and Christmas cactus are short-day plants.
Long-day plants need 14 to 18 hours of light per day. Vegetables and most garden plants are long day, and get pale and stretched when they don’t get enough light.
Day-neutral plants like geraniums, coleus and foliage plants are happy with eight to 12 hours of light throughout the year.
• Kinds of grow lights. There are many kinds of artificial lights that will support plants indoors, from ordinary bulbs and tubes to super-efficient LED lights. Most are available in multiple color spectrums.
Fluorescent tubes put out three to four times the light of incandescent bulbs for the same energy. Their color frequencies run from reds to blues, so you can mix and match to suit your preferences. Full-spectrum or sunlight fluorescents are great for all plants and for starting plants from seeds. They’re often even marketed as grow lights.
Industry standard, T-4-size tubes fit in ordinary shop lights and household fluorescent fixtures. New, smaller T-8 and T-5 tubes need fixtures with special ballasts, but use less power and last significantly longer. Cool-white and warm-white fluorescent bulbs can be mixed in a two-bulb fixture to get a good balance of red and blue light. Metal halide lamps and mercury vapor lamps have a strong blue spectrum, high-intensity light good for developing dense, stocky foliage. High-pressure sodium bulbs emit yellow-orange light that’s better for the flowering and fruiting phase of a plant’s lifecycle.
The newest technology for grow lights uses Light Emitting Diodes. LEDs are extremely energy efficient; they average 50,000 hours of useful operation, and generate very little heat, making them safe for plants and people. You’ll spend a good bit more upfront but you can expect to save 40 percent to 75 percent on your energy costs.
Regardless of which kind of lighting system you use, rotate your plants one or more times each week to balance the amount of light each plant receives. Replace fluorescent tubes when the ends start to blacken to keep adequate light levels for your plants. Keep the plants far enough away from the light to prevent burning yet close enough to maximize the exposure these supplemental sources provide.
Joe Lamp’l, host of “Growing a Greener World” on PBS, is a Master Gardener and author. For more information visit www.joegardener.com.