“ELECTROCULTURE”

Evening Star, Issue 22382, 4 July 1936, Page 19

“ELECTROCULTURE”

INTERESTING DEVELOPMENTS ASSISTING PLANT GROWTH At a recent meeting of the Dunedin Gardening Club Air A. P.' Mackie, M.M., A.M.1.E.E., A.M.N.Z., Soc. C.E., gave an interesting and informative address on ‘ Electrooulture and Irradiation, or Electricity as an Aid to Plant Growth.’ In the course of his address Mr Mackie said;— An article in the * Electrical World ' of April, 1908, states: “Weak electric currents have been applied to moistened earth in order to determine their effect on plant life, and all the experiments made tend to show that under certain conditions rapid growth _ results from such application of electricity. A new use of electricity for obtaining somewhat similar results has been made by Mr G. Hartman, of Sunshine, Ontario. Canada, who converts the electrical energy into heat and applies the heat under a hot bed for vegetables and flowers. In the comparatively cold climate of Northern Ontario, a current of from 15 to 20 amperes ht a potential of 110 volts has been found to be sufficient for a hotbed for a family garden The heater consists of approximately 260 ft of No. 12 B. and S. gauge iron wire wound- on coils 2in in diameter.

A piece of Ijin pipe was used in winding the coil, winch was afterwards cut into seven parts and mounted on porcelain knobs on a piece of asbestos board, the coils being connected in series. Tim heater was placed under a rough board frame about Oft by Bft, the floor of which above the heater was covered with about siu of earth, two hotbed sashes being used to cover the top of the frame. Electrical energy was taken from a 110-volt circuit, and with a current of IS amperes good results were obtained. The beat was found to bo sufficient to keep the earth, always noticeably warm'and in the cold early spring weather tender flowers and vegetables grew - rapidly. In some cases growth was so rapid that the plants were largo enough to be set out to advantage, were it not for the danger of frosts.”

Note.—With modern soil-heating cable this same - effect can be attained with considerably less energy. Mr G. Jacobsen (Agricultural Engineer-in-Chief of Norway) used the same method in 1922.

The development of electric coil heating cable has offered new possibilities for the nurseryman and market gardener. It has offered a source of bottom heat at the turn of a switch,

Armoured Un-armoured cable, cable. requiring little attention and without the dirt and labour, inseparable from the manure hotbed which requires skill and experience for best results. The manure hotbed is but a fleeting source of beat lasting for_ a few weeks only; the spent manure is, however, a valuable asset for garden use. The earliest and steadiest progress in commercial application has been in Scandinavia and Northern Germany • as early as 1926 some 50,000 beads of lettuce were raised in Sweden in electrically-heated beds. France and America were later in taking up the subject, but considerable attention is now being paid to it in those countries, America now having tome 10,000 installations. As far as can be gathered, interest has been spasmodic in Great Britain, and application slow, although at least

eight firms manufacture soil-heating cable. A considerable amount of research has been carried out by C. A. Cameron Brown, B.Sc., at the Institute for Research in Agricultural Engineering, Oxford University. When the soil in a flower border, garden plot, or hot bed is to be heated electrically, insulated resistance wires, buried in tho ground, are connected to tho power supply. The resistance of the wire transforms the electrical energy into heat, which is conducted to the soil through the insulation of the wire, thus raising the temperature. The electrical system has many advantages over other methods of warming the ground. ■ It is simple, easy to manage, easy and cheap to install, easily adapted to all requirements, and, in addition, gives a perfectly’ uniform temperature over tho whole surface heated. The power consumption is considerably less than might be expected, and thanks to tho exceedingly good bent-accumulating capacity of the soil, the current need not bo turned on all the time, but only part of the day, which makes electrical soil boating an excellent equaliser. The amateur will welcome the soil-heating cable, since few amateurs are able to handle a manure bed properly. The cable methods offer just those points—-ease of handling, readiness, and cleanliness —which impress the amateur, and he is usually not concerned with the finer questions of running cost. . What is best suited to amateur work is a cable loaded at from 150 to 350 watts, suitable for a one or two-light frame. If the 700-watt sizes are used they should not he crowded into less than a two-

light frame, and it is almost essential that a thermostat bo used with this loadjng. MODERN METHODS OF PROCEDURE. The cable should be buried Tin to Sin below the surface of the bed and laid at Gin to 7iu centres. The wires should be looped out grid-iron fashion, the starting and finishing ends of the

cables both being located at the same spot. Damage to the plants, etc., may occur if the roots come in contact with the cable, so it is desirable to place the plants between the lengths of cable rather than immediately over the cable.

FORCING FRAME. The bed should be dug out to a depth of ISin and about Ift longer and wider than the frame. The pit is then filled to a depth of Bin with heat-insu-latiijg material, consisting of cinders or coke breeze, and the frame is placed in the centre. The space outside the walls of the frame is then filled with the insulating material and the inner surface covered with one inch of sand on which the cable is laid and covered with a further inch of sand. A screen of wire netting or canvas can then be laid, if desired, say a couple of inches above the cable, to protect it when the soil is changed, and the bed completed with the sufficient rich soil to bury the cable to a depth of about 6in. The purpose of laying the cable in sand is firstly to prevent deleterious action by the soil on the lead alloy sheath; and with the same object, it is sometimes recommended that the cable should be laid in earthenware pipes. These types of protection ate mentioned only to indicate the various methods in use; where soil is rich in humus its heat conducting qualities are poor, and if the sand were omitted high temperatures concentrated hero and)

there would result, instead of a good general distribution of heat. Both before and after erection, care should be taken to see that the cable does not become damaged. Although the cable is -strong enough for all reasonable handling, it has only limited strength. Should the wires cross one another at any point, a small piece of stone or brick should be used to separate them, otherwise overheating will occur at these points. ’ In the electrically-heated forcing frame the temperature can bo auto-

A diagramatic representation of a garden frame with soil-heating cables installed. matically maintained by a thermostat, which may he sot f° r tho most suitable temperature for the particular plants being raised. Soil temperatures of ,45 to 70deg Fahrenheit are usually recommended for hotbeds, tho lower temperatures being used for growing cabbage, cauliflowers, lettuce plants, etc., a

medium range for tomatoes, and the higher temperature for cucumbers. _ The foicing frame may be readily converted to a cold frame for hardening plants by adjusting thermostat to approximately 40deg F. This is necessary so that the transition of plants to the ground will not be too abrupt. HOT HOUSES. In hot houses the cable is simply buried at a depth of six to 12in in the growing beds, with or-without the protective layer of netting or canvas, special methods of heat conservation being unnecessary. In many instances the houses will normally be heated the ordinary methods. The use of the buried cable will enable the temperature of the house to be reduced by about IQdeg, with a consequent economy on the cost of fuel. COLD FRAMES. For protecting cold frames against frost, the cable can be looped round the sides of the framej being attached to ordinary hooka or carried on small porcelain cleats. Control can be effected by any one of the following methods:—(a) Ordinary hand-manipulated switches; (b) a time switch which would automatically turn the heat on and off at certain pre-determined times. This method would not, however, take into account the temperature of the soil, etc. The time switch would be particularly effective in curtailing the use of current during the daytime when it was being metered at a price substantially above the night rate; (c) a thermostat can be fitted to keep the heat automatically at a constant temperature both day and night. The use of a thermostat, in conjunction with a time switch, maintains pre-determined temperature during the night, when .heat is most wanted.

For many purposes ordinary hand control will be sufficient, and is the cheapest means. Where economy of

current jor a critical temperature is not essential the time switch will achieve all that is necessary. With electrical heating the conservation of heat is absolutely essential. Wasted heat means wasted money. The power consumed in maintaining the temperature will depend on the efficiency of the heat insulation of the frames or houses.

The importance of these remarks will be better appreciated when it is stated that it is estimated that 60 per cent, of the vheat is lost through the bottom and sides of a raised bed which is uninsulated, whereas with a properly-con-structed —i.e., efficiently insulated—sunk bed the heat loss is reduced to 10 per cent. It is not necessary to touch upon horticultural topics, because electrical soil heating cables simply take the place of manure as a heating agent, and in no way affect other controlling factors, such as temperature in the greenhouse and humidity, which are left to the discretion of individual growers. Owing to widely differing conditions in the horticultural world one cannot give rigid data, as,so much depends on the locality and other conditions of cultivation. Experience has shown that the soil temperature can be definitely adjusted to encourage growth, whereas

under normal atmospheric conditions without the use of heated soil, such growth would be checked. Seeds germinate, plants grow, and cuttings root in from 20 to 30 per cent, less time. TIME TAKEN TO BREAK SOIL.

Substantial increases in the number ! of seeds germinated and increases of i from 10 to 50 per cent, iu cuttings I rooted have been reported; in fact, , rootings of cuttings have been successi ful by this resource where all other I methods were total failures. The writer will be pleased to supply gratis, detailed information, sketches, ! etc., to those interested in the practi- ■ cal application of electroculture. Mr ' Mackie's residence telephone is 20-807.

9 St3 flts FT3 o si * a C*J3 a, S wo— o-S Mean Mean Mean temp. temp. 60 F. temp. 77 F. 50 F. Bays. Days. Days. Runner b«ans ... 5 12 15 Cabbage -... 7 11 15 Turnip ... ... ... 3 5 6 Onion ... 8 13 15 Lettuce ... 3 7 8 Radish. ... ... ... 3 4 7 Parsnip • ... 10 16 18 Beetroot ... ... 5 8 — Mav June June