The Iowa Gardener: LED lights make starting seeds indoors less expensive

Indoor gardening enthusiasts, rejoice! Getting enough light for indoor plants used to be difficult and expensive, but now, thanks to the recent burst in LED technology, many of those old challenges are a thing of the past.

This time of year, lots of gardeners are starting seeds and those need plenty of light, usually more than a mere window can provide. Otherwise, the little plants will grow leggy, weak, and prone to rot.

Artificial lighting is useful to grow other things indoors, too, like lettuces and herbs. It also can be used to overwinter collections of plants, such as coleus, begonias, cactuses and geraniums. Or it can be used year-round to nurture permanent indoor displays of plants, such as African violets.

Getting good lighting for plants used to be problematic. One choice was an affordable but too dim florescent light set up. Another were reasonably-priced full-spectrum bulbs that fit into traditional fixtures, but they also were not very bright. Another option was various high-intensity grow lights, which were plenty bright, but were also very expensive, heavy, hot and fragile.

LEDS are game-changers because they have all the advantages of old-school lighting set ups without the disadvantages:

• Unlike the old florescent and inexpensive grow light setups of old, LED pack a lot of lumens (units of brightness) into a bulb. Yet LEDs are equally inexpensive.

• Traditional high-intensity lights provided enough light, but they were fairly heavy, creating challenges for the casual gardener who just wanted to create a temporary set up for seedlings. LED bulbs and the casing they come in are super lightweight, so you can hang them from a string from a ceiling or position them in any number of creative ways.

• LED bulbs also run far cooler than many high-intensity lights, which gave off so much heat they required running a fan or other ventilation to keep plants cool.

• LED lights are durable. They last far longer than a lot of traditional bulbs — for years rather than months. They are usually made of plastic, so they are break-resistant. That makes them easy to store offseason. It also means that they are easy to ship, so a huge variety is readily available online.

• Best of all, LEDs are far cheaper than old high-intensity light set ups, which could easily cost hundreds of dollars. They also were such energy hogs that they made a noticeable difference in your electrical bill. Not so with LEDs, which require a tiny fraction of the energy of high-intensity bulbs and also far less than incandescent or florescent bulbs.

Color Considerations

The trickiest thing about using LED lights is to find the right color of light. Different plants at different stages of their development need different light, sometimes measured based on the light’s appearance (with the Kelvin scale or K) and sometimes measured on the light’s wavelength (as nanometers or nm).

Different types of light promote different kinds of growth and health. But blue and red wavelengths are especially important for plants. Roughly speaking, blue impacts seed germination and foliage growth. It is expressed with a Kelvin rating around 5,000 or 6,000K, often called “cool” or “daylight” on light bulb packaging.

Reddish light boosts plant flowering and fruiting. It carries a lower Kelvin rating, often around 2700K or 3000K, often referred to as “soft white” or “warm white.”

Some gardeners say if you are growing plants indoors for just a couple months, as with seedlings, the color wavelength isn’t critical. Go ahead and use the same LED bulbs made for regular indoor use and choose those with one that has a “daylight” color, often listed on the package as 6,000 or so Kelvin.

However, the ideal is to use LED lights made specially for growing plants, labeled as “full spectrum.” No worrying about Kelvins and full-spectrum lights are a more sure bet for even healthier, more vigorous seedlings and better suited to plants you want to grow indoors for extended periods of time. They do cost more, but if you shop around, not significantly more than regular LEDs.

Brightness Considerations

The other thing to consider when growing plants is how many lumens bulbs throw off — how bright they are. A 100-watt incandescent bulb gives off about 1,600 lumens and a 40-watt bulb about 450 lumens. By way of comparison, two LED tubelike lights can put out almost 5,000 lumens.

If you are buying a LED light made specifically for plants, it will probably specify how far from the plants the light should be and the square footage of plants you can put underneath it.

If you are buying a regular LED light, it’s harder to figure out exactly how many lumens you need. But as a general rule, I’d buy the brightest possible, and look for at least 1600 lumens per fixture.

With a regular LED, I’d position the LED bulb no more than a foot above the plants. I’d also position plants so they were never more than 1 foot away from the perimeter of the light fixture. So if you had a 4-foot tubelike LED fixture, (which you can buy for under $10) I’d keep any plants in a 2 x 6 area directly underneath. If you have two of the lights, I’d position them two feet apart and set plants in a 4 x 6 area underneath. If you have a single LED light in the shape of a traditional incandescent light bulb, I’d put a plant or plants under it that spreads out no more than 2 feet.

If a bulb doesn’t specify the lumens, beware. Even if it bills itself as a plant light, it might be too small or dim for your purposes.

No matter what type of light set up you create, it’s important to turn those lights off for about eight hours a day. Plants, just like animals and people, need dark for healthy growth, too.

Veronica Lorson Fowler is co-publisher of The Iowa Gardener website at www.theiowagardener.com.