Climate plays a vital role in the growing of plant life indoors. But for a home hydroponic hobbyist, it would be both impractical and very expensive to try to control climatic conditions totally. This would necessitate keeping a tight climatic rein on the entire house, or at least a sealed-off room.

The three main factors to consider are light, temperature and humidity, factors that you can control to an adequate degree for indoor growing. Given proper attention, the control of these three aspects will definitely increase your crop yield.


Photosynthesis is the process whereby a plant utilizes certain colour wavelengths of light to manufacture energy. This energy is then used by the plant as fuel for growth. It is obvious to all of us that plants need some light each day in order to survive, and science has shown us that major photosynthesis activity takes place when the red and blue wavelengths are present. All plants have different light intensity requirements, ranging from a far corner of a room to brilliant sunshine.

Ifyou decide to grow hydroponic vegetables indoors, you must use artificial lights, because, in order to fruit, vegetables require high light levels to develop vast amounts of energy. Alternately, a good-sized window with a south or west exposure will probably allow you to grow herbs, leaf lettuce and possibly Tiny Tim tomatoes without lights. Remember, though, that too much direct sunlight through a glass window magnifies into an inordinate amount of heat that could ruin your crop. A shade of some sort should be used during the period of most intense sun. Beyond these three crops, lights are certainly better and in most cases necessary; but even when using them, it is a good idea to place your hydroponic unit near a window.

When arranging where to put your hydroponic tanks, or when purchasing a lighting fixture, try to use a light meter. In my experience, the minimum requirement is one thousand foot-candle power.* (One foot-candle power is the amount of light falling on one square foot of space located one foot away from a high quality candle.) It is true that you can grow indoors with less than this amount, but this depends on what you are growing, and certainly most vegetables should have the thousand or more.

For artificial lighting, you may use mercury vapour, sodium vapour, metal halide lamps, tungsten filament or fluorescent. Fluorescent lights are the most popular, and they can be broken down into several groups: Regular High Power Factor (Bi-Pin), High Output and Very High Output. Each is a different type of tube, and they are in ascending order of light output as well as price. Within each type, there is a selection of tubes of differing colour outputs; those that are useful to the indoor gardener are listed below.



Cool White The industry standard, and the least expensive — strong blue, medium red.

Warm White Medium blue, medium red.

Strong yellow and orange give it the appearance of red.

Plant Tubes Strong blue, strong red. Sold under various brand names, such as Gro-Lux and Agro-Lite.

Full Spectrum A new variety, resulting from research in photo-biology. Its spectrum is very close to sunlight, with low-level ultraviolet included. This concept looks promising for the future. Vita-Lite is the most readily available at present.

The type or combination of types is important, but really depends on what you are growing. A flowering plant requires stronger red than green leaf plants such as lettuce or house plants. Choose your lighting accordingly. One interesting way that this difference turns up is when herbs are grown under a Plant Tube, where they flower much sooner than under a plain Cool White tube. With some herbs, for example those you want to go to seed for later crops, this is an asset, but for others it is not.

The tungsten filament (light bulb) produces a spectrum that starts in yellow and goes through orange to red. It provides none of the blue that is needed for compact leaf growth. It is an efficient space heater, however, it that's what you want. Remember the above points and use the light bulb accordingly.

In their book. Gardening Indoors Under Lights, Fred and Jacqueline Kranz suggest that far red in the spectrum is very important and found that it is provided by the incandescent bulb. They also mention that it is essential to maintain a proper ratio of far red to red rays. This was first suggested by Dr. R. J. Downs, a member of the team that made impor-

tant discoveries in light spectrum analysis. The ratio of three watts fluorescent to one watt incandescent is the best according to these authors. Minor disparities, if not too marked, are acceptable. Therefore, when using four 40 watt Cool White tubes, you should combine them with two 15 watt incandescent bulbs.

Mercury and sodium vapour lamps are high pressure, high intensity and high priced. They are suitable for large areas of high intensity production. Their spectra are good for certain crops in conjunction with sunlight, as in a commercial greenhouse, but they are somewhat impractical at present for the family-sized, indoor hydroponic garden for two reasons. The first is cost. Many people do not want to spend three hundred dollars at an early stage of their new hobby. The second is the high heat output of these lamps, which in turn causes high temperatures. However, there is no doubt that this type of lighting will be important in the future. Michigan State University, the University of Guelph, the General Electric Company, Agriculture Canada and Washington State University have all been conducting experiments with mercury, sodium vapour and metal halide lamps. These lights, whose foot-candle power at source almost matches the sun's, could solve the problems of indoor and winter growing of vegetables.

Whatever kind of light you finally select, make sure it does not give off too much heat. Should you, for example, decide to use a flood light, it is important to remember that it produces a high degree of heat. The only effective way to overcome this problem is to fix the socket at a distance of two to four feet from your plants. Naturally, the farther removed from the plants, the less effective is the light supply. The correct approach is to employ a method that produces maximum spectrum; minimum, non-required heat; and considerable light intensity.

The minimum requirement of one thousand foot-candle power at the source can be achieved by using four 40 watt tubes that are forty-eight inches long. If you decide to use a twenty-four inch length, you will still need four tubes; they are now reduced to 20 watts, and the intensity of the light is reduced although not proportionately.

One fixture that is currently being tested may be another solution to the problem of lighting for indoor vegetable growing. It is a very high-output fixture using 110 watt Power Groove fluorescent tubes. These are still Cool White tubes that lack some of the red spectrum, but this may be overcome by using two or three 15 watt incandescent bulbs. Two main questions that are presently being probed are whether the increased intensity compensates for the lack of red in this arrangement and whether there is too much heat generated by the Power Groove. Excessive heat, of course, could cause crop burn, especially if the 15 watt bulbs are used to round out the spectrum.

The temperature underyour lights is of singular importance regardless of light intensity. Should the leaf temperature go above 85° F (29°C), the plant can no longer carry out photosynthesis to any great extent. Remember that leaf temperature can be considerably higher than room temperature. In this situation, a crucial part could be played by a small fan placed near the growing area to circulate air and keep the temperature within acceptable limits. Don't point the fan right at the plants.

The Power Groove tubes have over 2000 foot-candle power. This is the first time that anything over approximately 1200 foot-candle power has been available from fluorescents. In addition to expense, the problems of spectrum and temperature still must be solved to make the use of such high-output fixtures suitable for the indoor gardener.

On the cheaper side of the spectrum, it is possible to use Cool White tubes. As mentioned, the addition of two small incandescent bulbs of 15 watts each will help make up for the deficiency of red in these tubes. The materials to ask for are:

  1. Four medium, bi-pin, rapid start Cool White tubes
  2. Two 15 watt refrigerator bulbs. (These are smaller than a standard 15 watt bulb, lessening the danger of direct contact with foliage.)
  3. A mount, preferably with a hood, to hold these items.

Another combination that works well is two Warm White and two

COOL White tubes. As seen by the table below, deficiencies of spectrum can be kept to a minimum when tubes are used in combination.


Cool White Day Light Warm White Natural White


Violet-Blue Required by Plants good

Orange-Red Required by Plants good excellent deficient deficient deficient veiy good excellent

Ifyou are going to invest in the more expensive category of grow-tubes, it is worthwhile to get the best. In my opinion, this is the DurO'Test Vita-Lite medium, bi-pin rapid start tube. No extra tubes are necessary when using such a fixture, because four of these tubes produce enough red by themselves.

These recommendations don't discount the fact that there are mixed views by the experts on what is the best light source for indoor vegetable growing. Part of the reason for these divergent views is that nothing yet devised by man is able to totally replace the sun, which provides us with eight to ten thousand foot candle power on a bright day. Everything we use for indoor hydroponics is at best a poor second.

When setting up your own or buying a lighting system for your indoor garden, don't forget that most plant fixtures use only two fluorescent tubes, just enough for ornamental plants, but often insufficient for vegetables, some herbs and flowers. Your hydroponic system will need four tubes and at least one thousand foot-candle power illumination at the source. Even with the four tubes, depending on their kind, of course, power consumption can be kept as low as 190 watts, no more than a table lamp. On a dull, slightly overcast day, there is often more light outside than with a four-tube fixture.

Grovida Plants Indoors
Figure 13. Tall and short plants can be grown under the same light by raising the planter of small plants with bricks or blocks.

PRACTICAL USE OF LIGHTING Keep the light low over the plants. Two to four inches is reasonable. Vegetables, flowers and herbs need much stronger light than ordinary house plants. If they don't get it, they will grow weak, spindly and pale.

Raise the light source whenever the growing plants touch the tubes or bulbs. Two feet is the highest it should be raised; otherwise the lower plants won't get enough light.

Illuminate your plants sixteen to eighteen hours a day. An occasional night with the lights on is less harmful than a day with them off. To make things easier, plug the light into an automatic, heavy-duty, grounded timer - the kind that accepts a three-pronged plug.


Very High






Cantaloupe Corn

Cucumber Okra

Spanish onion





Brussels sprouts










Mustard Parsley Parsnip Pea

Radish Spinach Spring onion Swiss chard Turnip (medium to high)

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