Frames may be permanent or portable and they may have span or leantto roofs as in greenhouses. The pitch of the frame light (covering glass) is usually much less than that of the, but must never be quite flat. The standard light measures 6 ft. by 4 ft. or 3 ft. by 4 ft., but other sizes can be obtained. Depth of frames varies greatly according to requirements but is not as a rule less than 9 in. at the lowest point or more than 3 ft. at the highest.
Maintaining Temperature, An unheated frame, known as a cold frame, will not be proof against frost in winter. In consequence, tender plants cannot be kept in it with complete safety. Matters can be improved by covering it heavily with sacks or mats during frosty weather, but these are mainly of use at night, for if kept on for long by day, plants will become drawn through lack of light.
Heating can be effected by running hot-water pipes through the frames, placing small electrical or oil heaters in them, or by heating the air or soil with electrical warming cables. The cable is attached to the inside walls of the frame or buried a few inches deep in the soil. Alternatively the frame may be placed on a hotbed, i.e. a heap of decaying manure. Fresh manure is required and should be turned once or twice as for mushroom beds. As it starts to ferment it will heat. When the temperature in the centre of the heap has subsided to 75°-80°, it is trodden into a pit at least 18 in. deep and a little larger than the frame, or alternatively it is built up into a rectangular mound of this size and 18-24 in. high. Six inches of soil is placed on top and then the frame is set in. can be sown or inserted either in the soil or in boxes and plunged in it.
Ventilation. This can be given in three ways, by sliding the lights, by tilting them, or by removing them altogether. All are useful according to weather and condition of growth. When tilting lights, always do so on the side away from the wind. Frames are especially useful for hardening off half-hardy plants. This is done during April and May, and ventilation is gradually increased until the lights are removed altogether by day and finally by night as well.
Watering. General rules are the same as forin greenhouses. During rainy weather it is often wise to remove the lights for a time and let the plants get their moisture naturally, but do not do this if the rain is very cold or the plants of a kind that do not like moisture on their foliage.
Raising in Frames, General rules are the same as for greenhouses, but may be sown direct in a bed of soil prepared in the frame instead of in boxes or pots, if preferred. As a rule this is desirable only with strong-growing plants, such as vegetables and herbaceous perennials. February and March are the two months when the frame is most in use for , but it may also be required in June and again in August—September.
Cuttings in Frames, General remarks regarding cuttings in greenhouses apply. Frames are particularly serviceable for cuttings of hardy plants which need a close atmosphere, e.g. spring and summer cuttings, or those that appreciate shelter, e.g. evergreen shrubs. No attempt should be made to strike tender cuttings in frames unless they can be moved before cold weather arrives or the frames can be heated.
Frames in Summer, From June to September inclusive, frames can be used for many greenhouse plants that do not like high temperatures. A shaded frame will be serviceable for cyclamen, greenhouse primulas, calceolarias and cinerarias, and a sunny one for perpetual-flowering carnations, pelargoniums, etc. For some of these plants it may be necessary to increase the height of the sides.