Types of Greenhouses



The Greenhouse

Types of Greenhouses The popularity of greenhouse gardening today is proof of its pleasures. Even a modestly sized and equipped greenhouse can extend your gardening horizons in a quite remarkable way. It allows you to grow many plants otherwise beyond your scope, and the opportunities it provides for home propagation can add a new dimension to your gardening interests.

A greenhouse can easily be given year-round interest but it is never more appreciated than in winter and early spring before the garden has come really to life again and colour is everywhere. Even with a small greenhouse, there is so much you can do to brighten the dull days for flowering bulbs like the daffodils, hyacinths, freesias and tulips, and other plants like cinerarias and primulas need only modest heat. And if you are prepared to raise the temperature a little more, it is easy enough to have cyclamen and poinsettias in bloom.

Of the summer flowers, my thoughts turn first to the fuchsias and regal pelargoniums and for autumn, the glorious chrysanthemums.

Perhaps the most fascinating and challenging aspect of greenhouse gardening is that you make your own climate and, by manipulating the heating, ventilation and damping down, can provide the conditions required by the plants you choose to grow. As with everything else, experience has to be won the hard way. You’ll learn by your mistakes surprisingly quickly, though, most gardeners learn to know the idiosyncracies of their equipment and the quirks of their plants and soon achieve the success which it is so much desired to have with any hobby.

If you can afford it, the heated greenhouse is the best choice every time, but I must make the point that an unheated greenhouse also allows you to grow many showy and interesting plants superbly well. In winter, bulbous plants like the miniature cyclamen and small narcissi, which are perfectly happy in the open garden, can be flowered without the risk of their flowers being damaged by bad weather. And in summer plants like fuchsias and tuberous-rooted begonias, which are normally brought on in a heated greenhouse, can be flowered a little later in the greenhouse which must make do with the natural heat of the sun.


Types of Greenhouses

When deciding on a greenhouse there are various factors to take into consideration and the most important of these is the kind of plants that you want to grow. Are they tall growing or will they be pot plants for growing on staging; will you want to grow, say, a wall-trained peach or nectarine? These and other considerations must be thought about first, and I shall discuss the advantages of the different types of house available. Also there is the question of metal or wood. The former has advantages in that the non-rusting alloy frames are slim, to let in maximum light, and are impervious to the weather, but wood has a more sympathetic appearance in many gardener’s eyes and in the case of hardwoods such as Western Red Cedar, it does not need painting nor indeed any other maintenance.


The Span-Roof Greenhouse

This is the most adaptable kind of greenhouse for it is suited to a wide range of plants and there are various modifications of the basic design. For example, the standard span-roof house has low walls of brick or wood with staging on both sides at the level where the glass starts. Alternatively, you can obtain such houses with staging for pot plants and a wall on one side and glass to the ground on the other, to allow plants to be grown in a bed. Another alternative is to have glass on both sides to ground level to grow crops such as lettuce or tomatoes in beds on the floor and to follow these with chrysanthemums in the autumn.


The Lean-to Greenhouse (see image above)

This type is also popular for it makes use of the house wall on one side; saves money, of course, because the materials needed are less; and provides a wall on which you can train, say, a peach or nectrine or an ornamental climber. The house wall will also transfer some heat.


The Conservatory Greenhouse

This kind of house is once again becoming popular, but in a lighter, airier style than its Victorian forerunner. My own conservatory greenhouse gives me enormous pleasure, and if such a house is separated from a living room by a glass door the ease of access and the visual enjoyment is obviously far greater than it could otherwise be.


Dutch-Light Greenhouse

This type of greenhouse, constructed basically from standard Dutch Light panels, is excellent for tomatoes, lettuces and other crop plants which benefit greatly from the high light factor associated with its large panes of glass.


Three-Quarter Span Greenhouse

This type of greenhouse, which is a cross between the span-roof house and the lean-to, has many advantages but it is not seen as much nowadays as it formerly was. Like the lean-to it makes use of a wall for one of its sides, but the house in this case is higher than the wall and the short span from the ridge to the wall allows more light into the house than does the type just mentioned. Also this short span, or sections of it, can be hinged to allow top ventilation.


Other Considerations

Having outlined the advantages offered by different types of greenhouse let us now briefly consider one or two other points. Height is one of the key factors in successful greenhouse cultivation but it must not be bought at too high a price. Where the glass reaches to the ground the light availability must be better, but the heat loss is also greater. Also with large glass sections, as in a Dutch Light greenhouse, and a southem exposure, the temperature will rise rapidly in summer with sun heat and the consequent temperature variations during the day may not be too easy to control.

Door fittings and ease of access are something I always like to pay close attention to as well. Most important I consider is that the door should allow a wheelbarrow entry without the contortions impossible to make if it is carrying a load of plants or compost.

More important is the amount of ventilation the greenhouse you are interested in provides for. Ventilation must be adequate for the kind of plants you intend to grow. Roof ventilators are essential and side ventilators in addition will give more precise control of the temperature and air circulation.


Where to Position Your Greenhouse

As with so many things in gardening, choosing a site for a greenhouse is largely a matter of common sense. For obvious reasons it should be near the house (think of all that foul winter weather!) and within easy reach of electricity and water supplies, neglecting this point can be a costly business. Equally important,it should not be sited so that the house or trees cast unwelcome shade. For most of the year the need is going to be for more light than can be provided so that the site chosen must be the lightest possible, which conforms with the second criterion I mentioned. Try also to avoid draughty sites, for cold winds can lower the internal house temperature significantly; or if such a site is especially good for other reasons, do what you can to eliminate the draughts by screening with a hedge or fencing. North and east winds are, of course, the most damaging ones.

Lean-to and three-quarter span greenhouses are usually placed against south-facing walls. North-facing walls are not suitable as the small amount of light they receive limits too severely the number of plants which can be grown successfully.

01. December 2010 by Dave Pinkney
Categories: Greenhouse Gardening | Tags: | Comments Off on Types of Greenhouses

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