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Using indoor plant lights

Q: I’m interested in gardening under plant lights. What do I need to get started?

Leslie Arnold, Spring Green, WI

Plant lights give you another growing option when cold weather sets in. Plant lights give you another growing option when cold weather sets in. Photo/Illustration: Jennifer Blume

A: Horticulturist and garden designer Gary Keim, of Swarthmore, Pennsylvania, replies: For many gardeners, the gardening season is far too short. With indoor plant lights, the gardening season can continue despite weather conditions or light limitations. You can use plant lights to start seedlings, to overwinter cuttings of tender plants, or to grow a special collection of plants, such as succulents, orchids, or African violets.

Here are some basics: Plant lights for home gardening are usually fluorescent tubes mounted above shelves or a table. To ensure proper plant growth, it’s best to use full-spectrum light bulbs, which provide the full complement of light waves to plants. They are sold by garden suppliers as “grow lights.” You can achieve a similar effect with a fixture that holds two tubes by combining a warm- and a cool-fluorescent tube. You can buy prefabricated units with multiple shelves that hold the lights, or you can put together your own set-up using standard fluorescent fixtures. Whatever you choose, make sure to hang the fixtures on adjustable chains, so you can raise and lower the lights as needed.

Consider the light requirements of your plants to determine light placement. The output of light is measured in foot-candles. The closer plants are to the light source, the higher the foot-candles or intensity of the light they receive. For seedlings or other plants with high light-intensity needs, such as cacti, the distance between the lights and the plants should be 3 to 4 inches. For foliage plants tolerant of lower light levels, the spacing could be a foot or more.

Wherever you choose to place your plant lights, make certain the air temperature is suitable for the plants you’re cultivating. It would be futile to grow tropical orchids, which like warmth, in a cold basement. Annual seedlings may germinate more rapidly in a warm environment, but their growth will be stockier and healthier if temperatures are cooler.

Using some type of fan will enhance air circulation and reduce the threat of fungal problems. Remember to check the moisture level of your plants every day or so, since plants receiving intense light grow quickly and often dry out fast. Bottom watering is best for seed­lings; place the pots in a waterproof tray and add 1/4 to 1/2 inch of tepid water to the tray. The soil will wick the water to the seedlings’ roots. Also, be sure to fertilize your plants with a water-soluble liquid fertilizer on a regular basis.

Since plants require a period of darkness for good health, it’s wise to put your lights on timers—14 to 16 hours of light is sufficient for plant growth and flowering.

From Fine Gardening 74, pp. 80