GLASSHOUSES, CLOCHES AND PLASTICS

Taupo Times, Volume VI, Issue 289, 22 August 1957, Page 3

GLASSHOUSES, CLOCHES AND PLASTICS

Many keen home gardeners have at times wished they could own a glasshouse, writes the gardening correspondent. Its advantages are obvious when one considers the possibilities of raising those earlier tomatoes, or seedlings, or indulging in growing flowering plants which require some protection, such as begonias, cyclamen, or even orchids. One of the main disadvantages is the initial cost, and in many cases the danger of breakages. Glasshouses are inflexible, the giass is easily broken, and the supporting structure must be heavy and rigid. Once erected, they are not easily repaired, so that the framework must be constructed of high-quality materials. All this adds up to expensiveness. In recent years there has been considerable interest in the possibility of using plastics to replace glass for horticultural purposes. Over the last two or three years this has been achieved to a considerable extent by using thin sheet plastic as a material for covering glasshouses, frames and cloches. Since there has been so much interest from home gardeners it may be worth while discussing the use of plastics in this respect. The object of using structures such as glasshouses is to create a more favourable environment for the growth of plants. The plastics seem quite capable of playing their

part in this. They shed off the rain, keep out the wind, admit the light and retain the temperature which | has been built up inside the structure. They are easily attached to the structure itself, and, since they are quite fiexible, they ' can easily be built into any shape. Finally, they are cheap, being from one-tenth to one-twentieth the price of glass. Disadvantage On the other side of the picture, however, there is a disadvantage. Most of the plastics available are gradually degraded by the sun, so that the plastic film n'eeds replacing every one or two years. This may be regarded as a nuisance, but the job is not a very arduous one. Several forms of plastic are available for this purpose, but not all are equally suitabie. Polythene is the material which has so far been used for this purpose, partly beeause of the fact that it has proved very "satisfactory and also partly beeause it is one of the cheapest plastic materials of its type. It is available in a wide range of thicknesses from one-thousandth of an inch upwards and in widths of up to six feet or more. Polythene does not harden in cold weather, nor does it become excessively soft in warm weather. For glasshouses I have found that five-thousandths of an inch gives very good results, but for cloches half this thickness would be sufficient. The advantage of using the thinner film is purely one of economy; since the price of the material is based on weight, the thinner the film the greater area per pound. Polvinyl chloride film, often abbreviated to P.V.C., is also used in horticulture for the same purpose as polythene. Pure P.V.C. is brittle and so has to have the addition of a plasticiser to make it suitabie for this purpose. The value of P.V.C. film- depends on its plasticiser; the materials which I have tried have not proved entirely satisfactory, but overseas suitabie forms have been used for several years. Nylon Film Nylon is a plastic usually associated with stockings and brushes, but it can be made into a sheet film similar in appearance to polythene. It is tougher than polythene but is expensive and breaks down under the action of sunlight. % Terylene can also be made into film which is quite strong but tends to split. It aiso is expensive and breaks down due to the sun's action on the film. In the U.S.A. a new plastic material known as Polyflex 230 has been tried out. It is glass clear, and resists degredation by sunlight for up to 10 years. At present it is expensive and its use, at least for the home garden, remains problematical, and since it is not available in New Zealand it can be left out of our calculations.