Greenhouse Gardening: Design and Ventilation

My first greenhouse was constructed from old commercial greenhouse bars, running purlings, end rails and such like — needless to say it was a very much more laborious exercise than one would be expected to be confronted with now when contemplating the erection of a greenhouse. With second-hand material everything had to be cut, trimmed and somehow made to fit the chosen size of the house, whereas the modern greenhouse comes in a neat package with explicit and easily followed instructions for putting it together.

We hear many arguments for and against this and that type of greenhouse, and the various merits of each particular design. You can go through endless glossy catalogues in an effort to decide on the type of greenhouse that will be best suited to your needs, and the site you have, but it will be very much better for the would-be purchaser to take him or herself along to one or more of the many garden centres where a complete selection of greenhouses will be on display. Most greenhouses on show will be of metal construction, some will be in cedar wood, but there will be very few of the older style white painted timber houses. This is not to say that there will not be timber houses available for those who can afford the cost of upkeep — and there are still the specialist manufacturers about who will construct a timber greenhouse or conservatory to almost any shape that you may have in mind, circular or hexagonal shapes being quite within their scope.

Provided one has the time to maintain a timber greenhouse, especially with regard to regular painting, then it could well be the best choice, as almost any type of plant will look better for the fact that it is growing in a brightly painted timber greenhouse rather than in a grey aluminium framed house. Cedarwood greenhouses do not need painting in the conventional sense, but they will be much improved by regular treatment with teak oil.


The commercial growers of glasshouse products, who depend for their living from their efforts, almost invariably employ span-roof type greenhouses to accommodate their plants. This could well be a guide for the amateur grower who is contemplating the purchase of a greenhouse. Span-roof houses may vary in height, or in width depending on the crop that is to be grown, or the pitch of the roof may vary, but in most respects they will be very similar. The cedar-framed Dutch light greenhouse offers a span-roof with a slight variation in that the sides of the greenhouse are gently sloping, but otherwise there is very little difference in the interior capacity of the house when compared to the more conventional structure.

The lean-to greenhouse is positioned against a supporting wall, the dwelling-house for example, but is not so very different from the span-roof house if you think of it as simply half of the latter with the dwelling-house being utilized as a supporting wall. Where space is limited the lean-to house is often the most sensible answer, and there will be the added advantage that when it is placed against the warm wall of a house, the interior will be that little bit warmer and the wall will be ideal for growing many fine climbing greenhouse plants against.

When deciding on a greenhouse, give particular attention to the solidity of the structure, and in particular to the way in which doors and ventilators are fitted. Badly fitting doors and vents are an indication of poor workmanship throughout, and will inevitably result in costly heat loss. Be sure too that the house is fitted with guttering and down-pipes, as there is nothing worse than rain water being shed from the roof of the greenhouse and in time making a muddy mess all round. Furthermore, rain water collected in a water butt will be a very useful commodity once the business of growing plants in the greenhouse begins —particularly so if the house and source of water is some distance away.

Ventilation and light

Although you must be ever mindful of the high cost involved in heating a greenhouse this should not blind you to the need for purchasing a house that is adequately provided with ventilators. Costly and problematical it may be at times during the winter months to keep the greenhouse adequately heated, but it will be an equally difficult problem during the warmer months of the year to keep the temperature down to a reasonable level. This makes it necessary to have reasonably large ventilators on both sides of the roof of the greenhouse and in the side walls also if the growing plants require maximum circulation of air. The door of the house can also be brought into play to aid air circulation on very hot days, but this may mean fixing a secondary door made of chicken wire if the neighbourhood cats are to be discouraged from using the house as a warm and comfortable retreat!

The glass of the greenhouse should be clear and the more slender the supporting structure then the more light will be available to the plants within the house, and adequate light is almost the most important requirement of the majority of plants that one will contemplate growing. The metal framed greenhouse scores in this respect, as it offers rigidity and strength, yet using comparatively slim glazing bars and supports.


21. October 2011 by Dave Pinkney
Categories: Greenhouse Equipment, Greenhouse Gardening | Tags: , , , , , , | Comments Off on Greenhouse Gardening: Design and Ventilation


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