WATERING, HEATING, VENTILATING AND SHADING 153 



rules can be made relating either to the amount of water 

 which should be used or the frequency of its application. 

 This operation calls for the exercise of good judgment. 

 The plants themselves tell the experienced grower when 

 they are in need of water. If they wilt or even appear to 

 droop, there is no question about their requirement, un- 

 less the heat of the house is excessive and the humidity 

 unusually low. The color of the leaves is a valuable 

 guide to the right amount of water. Light green foliage, 

 if temperatures are normal, indicates the use of too much 

 water, while a dark green color shows that this factor is 

 being properly regulated. Examination of the soil is also 

 valuable in determining when w r ater should be applied. 



Temperature of water. Much has been said in favor of 

 warming the water during the winter, before it is applied 

 to the beds. It is doubtful, however, whether instances 

 can be cited in which the use of cold water has actually 

 caused serious injury of any kind. Difficulties may arise 

 after the use of cold water, but the probabilities are that 

 they are due to cloudy weather or other causes rather 

 than to cold water. The fact is, if water is applied in a 

 fine spray, every globule will take on the temperature of 

 the air before it reaches the soil or foliage of the plants. 

 In sub-irrigation, where a stream of water is turned into 

 the tile, there may be some objection to using cold water, 

 but even in this case the water would soon acquire the 

 temperature of the soil. However, there is some evidence 

 that the use of warm water in sub-irrigation tile is an 

 advantage to crops requiring especially warm soils. 



Methods of watering. Various factors should be taken 

 into account in the consideration of different methods of 

 watering. Among them may be mentioned : 



(1) Cost of installation. The cost of installing a given 

 system may be slight, but if it is unsatisfactory there is 

 no justification for its use. 



(2) Effect on plant growth. One system may be better 



