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Let There Be Light
by John Harmon
November 29, 1999

At the beginning of every winter I start talking about the importance of supplemental lighting for indoor plants in the north. Many of the low light plants do fine even when light levels get down to six or seven hours a day. Most of the Tropicals that come from South America rely on 12 hours a day of filtered sunlight similar to conditions found on the floor of the rain forests. Many require higher levels of light and tend to die back here in the north or go dormant in the winter. You can prevent that with supplemental lighting.

There are a number of plant lights on the market and any of them will help. The best light is a combination of metal halide and high pressure sodium lights. Between the two of them you get a light spectrum closest to natural daylight. Get ready to shell out some serious bucks for the fixtures and the bulbs. Over $300.00 each. The worst drawback to these lights is the cost of operation. These lights eat up the bucks and you can expect a 400 watt metal halide light to cost you $30.00 a month using it just 12 hours a day. It will however provide enough light to cover a six foot square area with a reflector. This light produces a very bright "white" light and by itself will supply enough of the spectrum for growing most plants and vegetables. The high pressure sodium lights provide a spectrum closer to that of the setting sun. The 400 watt one will cost more for the fixture and the bulb but they will cost slightly less to operate and the bulb will last longer. I've tried both types and found they cost more than the plants are worth . At least the types of plants that won't kindle the interest of the local R.C.M.P.

The most inexpensive are the incandescent flood light bulbs that are called "plant" lights and screw into an ordinary light fixture. They come in wattage's from 60 to 250 watts but are the most inefficient. They supply very little light for the watts used. Another disadvantage to incandescent lights is that they produce a lot of heat and must be used so far from the plants that what light they do provide isn't worth the cost in electricity. Especially here in the north where to cost is high.

A better alternative is fluorescent lights. The 4 foot, two bulb, fixtures are less than $30.00 here in town and 4 foot plant bulbs are less than $7.00 each. The fixture is only 40 watts and inexpensive to run. I use two four foot fixtures side by side. That arrangement will cover a two foot wide shelf that accommodates the length of standard greenhouse trays for cellpacks which are twenty one and a half inches by eleven inches. You will be able to get four trays under each set of four foot fixtures. If for instance you were starting Geraniums at the end of February you would be able to fit 18 four inch pots in each tray for a total of 72 plants under each set of fixtures. I use the trays for larger pots too so I can just pour water or fertilizer solution into the trays to water from the bottom.

I hang the fixtures on light chain from hooks so I can adjust the height. To be effective fluorescent lights should be just a few inches above the tops of the plants. As the plants grow I raise the lights to keep the right distance. Fluorescent lights don't give off as much heat as the other types and can be used very close to the plants without danger of burning them. The new energy saving compact fluorescent lights would be better and could be used for rooting but I have yet to see full spectrum plant bulbs offered for these fixtures to grow plants beyond the rooting stage. I anyone knows of full spectrum bulbs available for these fixtures I would love to hear about it.

Which bulbs you use will depend on what you are growing. I use all "cool white" bulbs for starting plants from cuttings. These bulbs seem to help cuttings root faster. Once plants get going I switch to full spectrum plant bulbs also sometimes called "plant and aquarium" bulbs. These bulbs lose some of their intensity over time and should be replaced every season.

The time that the light comes on and goes off is also important, so a timer is a must to insure the light stays on a regular schedule. It will take 16 hours a day of florescent light to equal 12 hours of natural light. I run mine from six in the morning to ten at night. That takes advantage of what light there is during the short Yukon winter days.

It also helps light my living room as I have the shelves up high along the south wall. I can use all the light I can get in the winter. The fixture can also be mounted on the bottom of a shelf and the shelf below used for plants or rooting cuttings. You can adjust the height of the plants with blocks under the trays when the lights are fixed and can't be moved. There are fancy sets of shelves and lights available from some catalogues but generally they cost more than they are worth. Get a cheap set of book shelves that are adjustable. They will only give you room for one fixture on the bottom of each shelf but are half of the price of the fancy ones with all the chrome.

With a little extra light your plants will continue to thrive even when the snow is piling up outdoors and the mercury has disappeared in the thermometer.

John Harmon owns and operates Tropicals North. Write to John at The Real Dirt, c\o 211 Wood St., Whitehorse, YT., Y1A 2E4 or e-mail

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