80 GARDEN FARMING 



unless some system of conducting the heat through tiles placed in 

 the soil can be devised. 



Watering. There is no one feature of greenhouse management 

 which is more important than the supplying of water. Since nearly 

 all the forcing crops contain a large percentage of water, lettuce 

 and cucumbers being over 90 per cent water, the importance of 

 this factor is at once evident. The method of watering is also 

 important, because certain plants, like lettuce, with a large leaf 



FIG. 26. Bench built of brick and split sewer pipe for subirrigation 



surface close to the ground, are susceptible to attacks of fungi, 

 which destroy them if the surface of the ground is too wet. This 

 has led to a system of watering called subirrigation, which means 

 simply a method of applying the water to the soil beneath its sur- 

 face. This can be accomplished by constructing from lumber, 

 cement, or metal, a bench with a tight bottom, and providing 

 means of distributing water to the plants in the lower strata of 

 the soil, either through drain tile or perforated metal pipes, or by 

 placing hollow bricks upon the bottom of the bench. Another very 

 satisfactory method is to use split sewer pipe, laying it perfectly 



