IN the old days greenhouses were often put up to be a joy in themselves, like the smaller greenhouses at Kew which are filled with a profusion of flowers at all seasons. Such structures were given temperate heating all the year round, and on the whole were rather a liability in the garden. With the corning of the small man and allotment-holder. however, the advantages of the greenhouse became much clearer, and it is a common thing to see home-made greenhouses erected during that period still in use for the conventional routine of greenhouse cultivation seedlings, tomatoes and chrysanthemums in
that order. Most " allotment" greenhouses are unheated.
During recent years, and especially because of the war, the advantages of using a greenhouse properly have become manifest. Nowadays a greenhouse is definitely an investment. There is nothing to stop the investment producing beauty as well as profit; but these are harder times, and we like to have it both ways. Greenhouses are more expensive now than before the war; but the use of newer materials (both in timber and in metal) makes them more durable and efficient. There is no advantage whatever in buying a cheaply-made article if cheapness is the result of indifferent work or second-rate materials. Some of the newer houses made with red cedar or other durable woods can be obtaMed from firms which previously specialised in wooden structures, while a number of new competitors offer houses of aluminium alloy or steel.
Let us take the conventional shape of house first. This type is offered by producers of wooden houses in rot-proof timber which does not demand painting. Newer types are ideal for cross ventilation. On the whole, these are likely to hold their own with any of the newer products; but increasingly the need has been felt for greenhouses which can he expanded (or even contracted) to suit requirements, and in consequence houses of conventional shape are being offered which are constructed of Dutch lights. Dutch lights are large framed pieces of glass frequently used in commercial horticulture. Houses of this pattern are rather more squat than the usual type, and frequently have their gangway below soil level. Drainage must be seen to in this case. A house made of Dutch lights has obvious advantages as a temporary structure; but it is good also for certain types of permanent work, especially for forcing and for salads.
METAL GREENHOUSES Metal greenhouses are often of
strictly conventional shape. Some of the early models were viewed with disfavour because of the poor workmanship of their spot welding. But newer productions are splendid in every way, and I must say my fancy has been taken by some of the aluminium alloy greenhouses. These embody the latest principles; for example, they can admit light almost down to the ground, they provide good ventilation, and some of them have an almost square base on account of their slightly sloping sides, so that the maximum amount of ground is covered by the one green
house. I am informed that some of the more ambitious " squarebase " houses may be mechanically less secure than oblong houses; but that remains to be seen.
Metal houses do not harbour slugs, earwigs, moulds and woodlice in quite the same way as wooden ones. When they are well constructed their parts tit beautifully, and are not as likely to sag or swell as wooden parts. They are of the simplest construction and with ordinary use should last a lifetime. Several of the newer features arc noteworthy. All-round ventilation can he secured without *draught, and condensation and " dead " pockets of air are considerably reduced. Glazing is easy, and in certain types of house the substitute for putty consists of a rubber-like preparation which stays " put as long as required but can afterwards be removed with ease.
HEATING The cold greenhouse is the thing for nearly every greenhouse owner; that is to say, one which is heated by the sun only. But a house which is cold for the greater part of the year can have its value considerably enhanced by having a heating plant installed for spring and autumn use. This adjunct extends summer-andspring by about two months at each end with little expense for the moderate increase in temperature called for. The old-time boiler has its advocates and is economical for commercial use; but the amateur will probably feel much more attracted to the newer type of heater. especially
electric heaters. For high artificial temperatures, electricity is expensive; but for the moderate fillip to outside temperatures and for protection against frost, the electric heater with thermostat and cut-out is very economical. Of course, it requires no stoking or supervision, though ventilation will have to be provided by the owner as required.
Underground heating by cables is a coming thing, and commercial concerns as well as amateurs are increasingly drawn to this type of
warmth. It is surprising to see a thriving house full of precocious plants with moderate air temperature -all because the roots find warmth and encouragement where it is needed.
E. J. KING.