Research work and experimentation are developing a rapidly increasing amount of new knowledge and methods that may revolutionize the art of growing plants.
There has been considerable publicity regarding liquid nutrients, like growing plants in water containing various chemicals or sand watered with nutrient solutions.
These methods have produced remarkable crops — artificial light can be applied with equally good results whether plants are grown in soil or liquid nutrients.
Unquestionably artificial light is playing a rapidly increasing part in horticulture. Doubtless, the day will come when many of the more valuable plants will be grown in windowless greenhouses made of heat-insulating material.
In such a house, the advantage of the ever-increasing efficiency of light sources will be taken.
Lamps that operate at 50 or more lumens per watt are now available, or approximately three times the efficiency of comparable tungsten filament lamps. As a result, the cost of electricity is steadily decreasing.
Controlled Humidity and Temperature
The lamps’ heat will be used to heat the greenhouse in winter. Humidity, as well as light and temperature, will be automatically controlled.
Carbon dioxide may be fed to the plants. Sterilized soil will be used and likely contain liquid nutrients.
Under such conditions, parasites and plant diseases can be greatly reduced if not eliminated. In the future greenhouse, it should be possible not only to predict but to regulate almost to a day the blossoming date of any plant.
Considerable attention is being given to growing plants entirely under artificial light, not with the thought that this can be done on a commercially profitable basis. However, with ever-increasing efficiencies of light sources and decreasing power costs, this may come.
Why They Grow Plants Under Artificial Light
The U. S. Department of Agriculture is growing plants entirely under artificial light to eliminate weather, climatic, and seasonable variables, enabling them to study plant diseases and develop better control methods.
Some curious things are being discovered by using different light sources. For example, tomato plants will not grow under continuous illumination from Mazda lamps. However, they have been grown under continuous light from sodium lamps.
Under these conditions, albino leaves have developed. But fine dark foliage develops if just a little light from high-intensity mercury is added to the sodium for as short as two hours per day.
Perhaps the time is not far distant when we know the relative effectiveness of each wavelength of the visible spectrum for—plant growth.
The new germicidal lamps will undoubtedly find applications for killing mold spores and fungus growth, reducing air-borne bacteria, and disinfecting water.
With this data, light sources can be developed that will be so effective for plant growth that we can grow plants 100% percent indoors on a commercially profitable scale.
Heat-Insulated Greenhouses
The Boyce-Thompson Institute for Plant Research spent two years developing a radically new and different type of greenhouse.
Instead of being made almost entirely of glass, this house has a floor, four walls, and one side of the roof made of opaque heat-insulating material.
The house is lighted by 500-watt Mazda lamps in dome-type reflectors mounted on approximately 3’ foot centers. A thermostat controls these.
There is no heating in the house other than the heat generated by the lamps. This means eliminating one of the high costs of greenhouse operation during the Winter.
On sunny days, even in below-zero weather, the radiant energy in the sun shining through one side of the glass roof (southern exposure) provides more than sufficient heat inside the house.
During cloudy weather and at night, the heat is furnished by the lamps, which are automatically turned on and off by the thermostat to maintain any desired temperature. The light from the lamps also stimulates plant growth.
Due to the airtight construction of the house, carbon dioxide gas can be used economically in this house. Two very interesting methods have been used to supply this gas. One is by evaporating dry ice.
The other is by having a henhouse adjoining the greenhouse and forcing the air from the chicken house through a water bath (to remove ammonia fumes) into the greenhouse.
Hens give off relatively large amounts of carbon dioxide gas, which is of material benefit to plant growth when forced into the greenhouse.
Sun-Porch Greenhouse
Many glassed-in sun porches are seldom used in the winter — which, except in locations where Winters are extreme — could be converted into greenhouses at relatively low cost.
All that is necessary is to insulate and install thermostatically controlled 500-watt Mazda lamps and reflectors similar to those used in the heat-insulated greenhouse, put the plants under them, and have the fun of watching them grow.
This idea should enable the conversion of many sun porches, now more or less useless during winter, into beauty spots for the private homeowner.
44659 by Lawrence C. Porter