374 GREENHOUSE MANAGEMENT. 



ence in treatment was begun when the plants were set 

 in the benches. 



By sub-irrigation, clamping off is reduced, the soil 

 does not harden, and less attention is required than 

 when surface watering is practiced. It is particularly 

 recommended for the fh"st watering after the seed is 

 sown, to prevent washing of the soil and baking of 

 the surface. 



In the benches sub-irrigation is accomplished by 

 means of two and one-half or three-inch drain tile laid 

 two feet apart on the bottom, either lengthwise or cross- 

 wise, and covered with soil to the ordinary depth. Gas 

 pipe, with holes drilled at frequent intervals, may be 

 employed, but the cost is greater. Our best results 

 have been obtained with tile laid on a level, crosswise of 

 the benches. Long runs of tile are not always satisfac- 

 tory. If iron pipe is used the holes should not be more 

 than two feet apart, and not larger than one-fourth 

 inch. If long runs are used the pipe must be larger 

 than for short runs, and in all cases the capacity of the 

 pipe must be greater than the combined capacity of the 

 small holes. The tile may be laid end to end closely, 

 without cement, but ordinarily a more even flow is se- 

 cured if the joints are lightly cemented and then broken 

 just before hardening, so as to make cracks of uniform 

 size. 



The water may be introduced by boring holes 

 through the side boards of the benches, or a T joint 

 used, or, what is still hetter, a curved joint of sewer 

 pipe of same size as the tile. When the beds are to be 

 irrigated, water is introduced into the pipe or tile 

 quickly, and allowed to run full length, when it soaks 

 out uniformly through the adjacent soil. 



Sub-irrigation pre-supposes a water-tight bench 

 bottom. This may be constructed in various ways, but 

 the cheapest plan is to use ordinary barn boards, with 



