WATERING, HEATING, VENTILATING AND SHADING 157 



(9) According to growers who have had considerable 

 experience with this system, over-watering is impossible 

 when water is applied through tiles laid in beds that are 

 not water-tight. This unquestionably is one of the great- 

 est advantages of sub-irrigation. 



(10) Larger yields are often obtained with sub-irriga- 

 tion. 



This method of watering, as seen in Fig. 53, may be 

 used on raised benches as well as in beds on the ground. 

 It is necessary, of course, for the benches to be water- 



Fig. 53. Tile laid in bed for sub- irrigation. 



tight, which involves an additional expense that must be 

 charged to the cost of installing the system. Inasmuch 

 as benches are not generally used in extensive vegetable- 

 forcing establishments, it is seldom that we find benches 

 constructed for sub-irrigation. Aside from the expense, 

 it is a simple matter to make reinforced benches with 

 concrete bottoms and sides which will be entirely water- 

 tight. Such beds should be not less than 6 inches deep. 



B. H. Thome, who had 12 years of experience in the 

 use of this system, claimed that it is not desirable to have 

 the ground beds water-tight, because there is then no 

 danger of over-watering. There are two main points to 



