This section is from the book "The Standard Cyclopedia Of Horticulture Vol2", by L. H. Bailey. See also: Western Garden Book: More than 8,000 Plants - The Right Plants for Your Climate - Tips from Western Garden Experts.
: Inula Helenium.
Electro-Horticulture is a term used by Siemens to designate the application of the electric light to the growing of plants. The term is an unfortunate one, since the use of electric light is not an application of electricity to plant-growing, but is a way of securing illumination. Any strong artificial light hastens assimilation and thereby causes plants to grow more rapidly. The practical questions to be considered are, therefore, the expense of using the light, and whether there are injurious elements in the spectrum of the given light.
The spectrum of the electric arc light is the spectrum of carbon plus that of certain gases incident upon combustion. The spectrum of the arc light is rich in rays which light beyond the luminous part, and these rays are very injurious to most plants. These rays of the ultra-violet part of the spectrum are eliminated by a plain glass, so that when the electric light is surrounded by a globe, or when the light is hung above the roof of the greenhouse, the injuries are reduced to a minimum. Experiments at Cornell University showed that each kind of plant behaves in its own way in the presence of electric light. It is not possible to prophesy what the results may be in a given species, without experiment. A few plants, as tomatoes, cucumbers, melons and carrots, seem to be very little affected either injuriously or beneficially. Nearly all flowers are hastened into bloom by the influence of the light, and their colors are often brighter than under normal conditions; but in very many cases they do not last so long. The best results are secured if the light is applied to the plants when they have reached nearly or quite their full stature. If applied very early in its growth, the plant tends to make flowers before it has attained sufficient size.
In floriculture, therefore, the practical value of the electric arc light seems to be its influence in hastening the flowering of certain plants in dark climates, or when plants must be had for a definite season. For example, if the light is applied to Easter lilies for a month before their normal blooming time, the period of bloom may be hastened four to ten days.
Lettuce has shown greater beneficial results from the application of the electric fight than any other plant with which careful experiments have been made. Lettuce which receives fight from the arc lamp for half of each night may be expected to reach marketable size from one to two weeks before that which is grown in normal conditions.
As a rule, better results are secured when the light runs only half the night. A common two-thousand candle-power light has a marked effect on the growth of many plants at a distance of sixty to even one hundred feet. The incandescent light has a similar influence, but not so marked. It has no injurious effect, however.
As now understood, the application of the electric light to the growing of plants is a special acceleration to be used when the climate is abnormally cloudy or when it is desired to hasten the maturity of crops for a particular date. Only in the case of lettuce is it yet thought to be of any general commercial importance; and even with lettuce, it is doubtful whether it will pay for its cost in climates that are abundantly sunny. For the literature of the subject, consult the publications of the experiment stations of Cornell University and of West Virginia. See the article Light, Vol. IV.
Electroculture is a term employed to designate any culture of plants under the influence or stimulus of electric currents. The electric stimulation may arise from the electrification of the atmosphere in the immediate vicinity of the plants, or from the application of electric currents to the plants themselves. In either case, electricity exerts an appreciable and often a very marked influence, resulting in accelerated germination and growth (see the discussion, pp. 30-35, Vol. II, Cyclo. Amer. Agric).
In recent years much more attention has been given to the stimulation of plants by electricity directly through the atmosphere than through the soil. According to experiments made at the Massachusetts Experiment Station, this method appears to be successful and offers a most promising field for future research. Of the various methods used to stimulate plants by electricity, direct currents applied through the soil prove less valuable than alternating currents or static charges. In a series of experiments made with radish plants in closed glass cases, an average increase of 50 per cent was secured, and in another case 45 per cent increase when the case was charged from a static machine with an average potential of 150 volts for a few minutes each day. There are some obstacles in the way of electrically treating plants by the use of high tension wires or static machines owing to the possibility of grounding through steam-pipes and iron posts, and nothing very definite has been obtained as yet from this method. High tension wires (100,000 volts, more or less) have been used in the field with fairly good results, but winds affect a charged atmosphere to a certain extent.
The use of high poles provided with points to collect atmospheric electricity has proved successful in laboratory experiments for the stimulation of plants and the fixation of nitrogen, and in the future probably some such method will become of practical use. At present the various methods cannot be considered as of great economic importance. (G. E. Stone.)