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Types of greenhouses and frames 1 Greenhouses vary greatly in size, shape and up by paths, doors and equipment such as Shapes and styles styles have come on to the market. These type to meet the widely different demands of heaters and water tanks. The second way of Greenhouses are either free-standing or lean- usually have flat oblong wall panels but some gardeners. This wide choice is not always calculating space is to consider the growing to, that is, supported on one side by a house also are geodesic in structure, miniature helpful to the beginner, who is often thor­ area in conjunction with the height at the or other wall. Free-standing houses may have versions of the vast space-dome-like Clima- oughly confused by the variety of shapes and eaves and the height at the ridge. These two straight or inward sloping walls. Roof shapes tron greenhouse at the Missouri Botanic materials. The basic factors which must be dimensions affect first the amount of grow­ may be a simple span, hipped or double- Garden. Some of the more recent designs considered are what the greenhouse is to be ing space for tall plants, such as tomatoes, hipped curvilinear. The "mini" lean-to is a have curved glass panels and an overall shape used for, the amount of money available, and shrubs and climbers, and second ease of structure much narrower than the usual lean- that suggests the great Palm House at Kew where the greenhouse is to be erected. access and comfort in use. In general, the to greenhouse. They are useful for the small Gardens in London. Certain circular styles When buying a greenhouse, carefully larger the greenhouse the cheaper each unit garden or where wall space is at a premium. have decided aesthetic appeal and can be­ assess the amount of growing space required. of growing space becomes, though this is less The smallest ones are too narrow to enter and come a feature or focal point in the garden. There are two ways of measuring growing apparent in those models where the walls maintenance of the plants is done from the In addition they contain a surprising amount space. The first is a simple calculation of the slope inwards. All too often the beginner outside. On sunny walls overheating can be a of space, as the central path of a traditional soil or bench area available, which tells how chooses a greenhouse which in time proves problem in summer. oblong structure is done away with. At many plants may be accommodated. Simply to be too small. If cost dictates a small green­ During recent years greenhouse manufac­ present however, they are more expensive in multiply the length of the greenhouse by the house to start with, make sure it is a model to turers have been seeking more original de­ terms of growing space than structures of breadth, taking account of the space taken which extra sections can be added. signs, and as a result circular and domed traditional shape. Types of greenhouses and frames 2 Another departure from the traditional tages, and the choice must depend upon the The crucial factors in the choice of shape Mobile greenhouses greenhouse is the use of a framework of use to which the greenhouse is to be put. If are accessibility, light transmission, and sta­ Commercial growers use mobile greenhouses tubular alloy or steel supporting a cover made crops are to be grown in the border, glass to bility and durability. Commercially-available of the Dutch light type, which can be pulled of plastic sheeting. Early models, still much ground is needed for light. If most plants will greenhouses can be expected to be stable, on a system of rails over crops. These allow a used commercially, are called tunnel houses. be grown in pots, a staging is essential and the though the site must be taken into account in crop rotation program to be followed. For Smaller versions of this simple pattern are wall area beneath it can be made solid. Brick, choosing a design. Plastic-covered houses, example, salad crops can be started on one available for the amateur, and welded frame­ wood or asbestos-cement half walls provide for instance, are less durable in very windy site in spring, then left to mature in the open works in a variety of shapes are made. useful insulation, cutting the heating require­ places. Accessibility covers factors such as while the house is moved onto a new site Generally these have a traditional outline but ments of the greenhouse. A compromise is door design, which is dealt with on page 9, where tomatoes are grown. some are dome-shaped. Plastic houses are to board the north wall only, gaining some and heights at eaves and ridge pole. Low- cheaper than glass-clad ones but have draw­ insulation with little effect on light values. built houses can be raised on a home-made Frames backs in use (see pages 10 and 11). Removable wooden insulation panels are plinth of brick, wood or concrete to give It is less easy to vary the overall design of a made for some designs of greenhouse. These extra headroom. Light transmission is critical garden frame and the basic traditional shape Design can be fitted in winter and removed when only in winter and early spring, for during the is still frequently met with. This is a shallow Greenhouses can be fully glazed, or they can crops are to be grown in the bed. Kick boards summer months more light is available than oblong box with one end higher than the have one or more sides boarded or bricked should be fitted at the base of glass-to-ground is needed by the plants. Thus light is only of other and sloping sides shaped to hold a lid up to staging height. Both styles have advan­ walls to protect against accidental damage. concern when planning very early crops. or light of glass or plastic. A useful size is Types of greenhouses and frames 3 4 x 6 ft. Double and multiple frames of this Cloches design can be obtained. Variations include Until comparatively recently, cloches were double span tops and glass walls with a made as units or sections, each one like an number of different patented methods of open-ended greenhouse in miniature, fitting opening. together to cover rows of crop plants. Made Light-weight metal or plastic frames can be of sheets of glass and a variety of patented moved around the garden and placed on metal clips, they were cumbersome and ordinary beds in different positions as re­ breakable but very efficient. Rigid plastic quired. Traditional forms have permanent sheeting has largely taken over from glass for bases of brick or wood. this type of sectional cloche. The most recent Frames can be built along the sides of half- , development is the tunnel cloche made of boarded greenhouses in order to benefit from strips of flexible plastic sheeting stretched The traditional cloche (a) was made of solid anchored with wire hoops. Plastic tunnel surplus warmth from the greenhouse. over a series of wire hoops along a row and glass in a bell form. Class sheets joined cloches (e) consist of long plastic sheets The simplest form of frame is just a light, held in place with further hoops over the top. with clips can be tent-shaped (b) or barn- bent over hoops and held with more a glass or plastic panel, placed over a shallow The ends are anchored firmly by burying shaped (c). Corrugated plastic sheeting (d) hoops. Plastic sheet attached to wire pit. This allows pot or container plants to be them in the soil. Ventilation is by pushing up can be bent over rows of crops and frames forms a tent cloche (f). hardened off. the plastic on the side away from the wind. Structure materials 1 The superstructure of a greenhouse may be Unlike the wood-frame greenhouses once Metal is a good conductor of heat and cold Wood made of wood, aluminum alloy or steel. Pre- widely sold, aluminum structures do not need and for this reason, condensation drip can be However wood greenhouses are still popular stressed concrete, used for larger houses, is painting. This lack of regular maintenance is a nuisance in metal-framed houses. This heat for aesthetic reasons. The attractive colors of too thick and heavy for smaller structures. a big factor in their popularity. conduction factor also means that metal redwood, cedar and cypress fit much better Steel is also used in greenhouse construc­ houses are colder, or cool more rapidly than into the garden than the color of bright Metal tion, either totally, as in some large commer­ timber-framed ones, though the differences aluminum or steel. Most custom-built greenhouses are made of cial houses, or in conjunction with an alloy in in temperatures between the two are small. Providing a wood house is properly con­ wood or aluminum alloy. The latter is now smaller ones. The steel must of course be gal­ Unless the regular maintenance of painting structed and secured to a brick or concrete by far the most popular material, being light vanized or treated in other ways to prevent and putty renewal is considered a pleasure, base and is initially treated with a wood pre­ and strong and easily extruded into the rusting. Although generally adequate, after aluminum or steel and aluminum houses are servative (if the wood is not naturally decay- necessary shapes ready for bolting together time the galvanizing treatment breaks down much to be preferred to the various wood resistant), there is every chance it will out­ on the site.

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