84 Diseases of Greenhouse Crops 



greenhouse irrigation. In subirrigation water is ap- 

 plied through tiles underground. 



Effect of Subirrigation on Vegetable Crops. In- 

 vestigations by Rane* have clearly shown that pars- 

 ley, tomatoes, long rooted radishes and spinach are 

 greatly benefited by subirrigation. Lettuce, espe- 

 cially, seems to be most favorably influenced by this 

 method of watering (fig. 12, a-c). Little is known of 

 the effect of subirrigation on flowering plants. In- 

 vestigations along those lines are especially desirable. 



From the health viewpoint, subirrigation should 

 appeal to greenhouse men. Where lettuce drop is 

 prevalent subirrigation seems to check it materially. 

 The same is also true of damping off. 



In the greenhouse, subirrigation may be adapted 

 to any form of bed used, whether raised or solid. 

 In either case the bed should be practically water- 

 tight. To prevent the rotting of wooden beds Taft t 

 , recommends coating the inside of the beds with a 

 cement made of one part of water lime and three 

 of sharp sand. This is made into a thick paste and 

 spread over the surface about one-fourth of an inch 

 thick. For a bed with tile or slate bottoms a simi- 

 lar covering will render them sufficiently tight. 

 With wooden benches it is desirable that the sup- 

 ports be close enough to prevent sagging of the 

 beds. In case of solid beds, a tight bottom about 

 eight inches below the intended level of the bed is. 



*Rane, F. W., West Virginia Agr. Expt. Sta. Bui. 33: 255-270, 

 1893. 



tTaft, L. R., Year Book, U. S. Dept. of Agr.: 233-246, 1895. 



