HEATING GREENHOUSES. 



133 



burning fuel to waste, and possibly, if not probably, keeping up too strong a heat. The 

 figures of manufacturers indicating the heating capabilities of their boilers are reliable, 

 and afford safe guidance. Horticultural builders of repute do not hesitate to make 

 themselves responsible for the efficiency of the heating arrangements of the structures 

 they erect, and vendors of boilers and pipes will give the same undertaking when 

 they fix them in position. Many gardeners and a few amateurs understand such work 

 themselves, but in the absence of the requisite knowledge it ma}^ be a costly mistake 

 to attempt it. For the sufficient reason that no boiler can be described as the best for all 

 purposes and positions, no particular kind can be generally recommended ; but it may 

 be stated that the horseshoe Loughborough boiler, or those much resembling it, are 

 the most popular among the owners of very small greenhouses. They are fixed much 

 as shown in Fig. 66, and do their work well, burning almost any kind of small fuel 

 without being very frequently attended to. For miniature structures there are boilers 

 heated by gas or oil, but these cannot be safe for plants (even if frost be excluded) if 

 the noxious fumes of combustion are allowed to enter the house. 



A few words may be usefully said, for the guidance of beginners, on providing and 

 maintaining the requisite heat in greenhouses. It has been said on page 127 that many 

 plants, such as are there named, will be safe when the winter temperature does not fall 

 below 40°, and more tender kinds when the minimum is 5° higher. If those tempera- 

 tures are somewhat exceeded in mild weather during midwinter, no harm will be done if 

 there is little warmth in the pipes ; danger lurks in highly heating them in severe 

 weather and forcing the temperature above the minimum named, as this weakens 

 plants and favours their enemies — insects. The subject of excessive heating will be 

 referred to under " Winter Management." 



When frost finds entrance to greenhouses, destroying cherished plants, it is the result 

 either of the insufficiency of the heating apparatus, or of mismanagement — often tbe 

 latter. It must be remembered that the greatest cold usually occurs about day-dawn, 

 which is just the time that greenhouse fires are apt to get low. This must be provided 

 against by having the temperature of the house a few degrees above the minimum, say 

 about 10 p.m., or when the fire is made up for the night. The pipes must also be more 

 or less warm then, according to the state and prospects of the weather. 



A sufficient body of fire is absolutely necessary for ensuring steady combustion after 

 being banked up with enough suitable fuel to last through the night. Attention to 

 these routine matters is of vital importance during severe weather, and not less so is 



