Greenhouses and Coldframes

In determining the type of equipment for starting early plants, the gardener must consider the temperature and other climatic conditions in his locality, as well as the nature of the plants to be started. Hardy plants, such as cabbage, need only simple inexpensive facilities, but such heat-loving, tender seedlings as peppers and eggplant must have more elaborate facilities for successful production.

In well-protected locations a coldframe or a sash-covered pit on the sunny side of a building usually suffices. In colder sections, or in exposed areas elsewhere, some form of artificial heat is essential. Where only a little protection against cold damage is needed, a coldframe in which a temporary bank of lamps can be placed may be sufficient.

The hotbed, lean-to, or sash greenhouse heated by manure, pipes, flues, or electricity are all widely used, the choice depending on conditions. A comparatively small plant-growing structure will provide enough plants for several gardens, and joint efforts by a number of gardeners will usually reduce the labor of producing plants.

The plant-growing structure should always be on well-drained land free from danger of flooding. A sunny, southern exposure on a moderate slope, with trees, a hedge, a board fence, or other form of windbreak on the north and west, makes a desirable site. Plenty of sunshine is necessary.

Hotbeds and other plant-growing devices require close attention. They must be ventilated at frequent intervals, and the plants may require watering more than once daily. Convenience in handling the work is important. Sudden storms may necessitate closing the structure within a matter of minutes. Plant growing at home should not be undertaken by persons obliged to be away for extended periods, leaving the plant structure unattended.

A tight well-glazed structure is necessary where the climate is severe; less expensive facilities are satisfactory elsewhere. Covers for hotbeds and coldframes may be glass sash, fiber glass, plastic film, muslin, or light canvas.

In the moderate and cooler sections of the country, standard 3- by 6-foot hotbed sash is most satisfactory. Even this requires supplementary covering with canvas, blankets, mats, or similar material during freezing weather. The amount of covering is determined by the degree of heat supplied the structure, the severity of the weather, and the kind of plants and their stage of development. Farther South, where less protection is necessary, a muslin cover may be all that is needed and for only a part of the time.

Many substitutes for glass as coverings for hotbeds and coldframes are on the market. The most widely used substitutes are various kinds of clear plastic film. Some of these have a lifespan of only one season, and others a lifespan of 3 to 5 years.

Clear plastic film transmits as much light as glass in the visible range, and more than glass in the ultraviolet and infrared ranges.

The film comes as flat sheets (on rolls) and in tubular form. Flat-sheet film is used for tacking onto wooden frames; the tubular form is used for enclosing metal tubular frames with a tight double layer of film.

Large plant hoods made from semicircular aluminum or galvanized steel pipe and fitted with a sleeve of tubular plastic film make excellent coldframes or seasonal row covers. When used in this way, a double layer of plastic film provides an air space that insulates against 4 degrees to 7 degrees of frost temperature change.

Electrically heated plant beds are ideal for the home gardener, provided electric rates are not too high. The beds may be built any size. Because they are equipped with thermostatic control, they require a minimum of attention. It is not possible to buy frames - completely equipped with heating cables, switches, and thermostats - ready to assemble and set in position. Fill the frames with soil or plant boxes and connect to a source of current. Small frames may be removed at the end of the season and stored; larger frames are usually treated as a permanent installation.