Moisture and Water Requirements 83 



of water equal to about three hundred times the 

 weight of the dry matter which they contain. The 

 amount of water in the soil is also an important con- 

 sideration. The more water a soil contains the less 

 air it will have. The presence of too much water 

 in the soil often brings about serious complications 

 in the health of plants such as suffocation of the 

 roots, weak growth and a loss in power of resistance. 



The improper use of water may affect the physi- 

 cal structure of the soil and injure the plants. The 

 careless dashing of water on the surface of hothouse 

 benches will compact and puddle the soil, and tend 

 to wash down the smaller grains to the bottom, 

 changing thereby the capacity of that soil to retain 

 air or heat, and thus indirectly affect the health of 

 the plants. 



Greenhouse plants depend on irrigation for their 

 water entirely. Surface watering is still in use by 

 the majority of hothouse men. But at best, this 

 method often does no more than pack the soil in- 

 stead of saturating it. Moreover, while safe enough 

 for the experienced grower, it becomes extremely 

 unsatisfactory when entrusted to careless or inex- 

 perienced labor. 



SUBIRRIGATION 



It has been hinted previously that subirrigation 

 has not found general favor with greenhouse men. 

 Yet this has proved both experimentally and in 

 practice to be far superior to any other form of 



