28 The Amateur's Book of the Dahlia 



Taking into consideration the natural habitat 

 of the wild dahlias on the volcanic mountain 

 sides, we can quickly understand that the 

 foundation of the soil is disintegrated rock, or 

 mineral soil, combined with decayed vegetable 

 matter. 



Lava is melted rock often mixed with burnt 

 rock or volcanic ash, and which has been hard- 

 ened on reaching the air. This after ages of 

 time is crumbled into dust by action of the 

 elements, forming a very fertile soil. The lava 

 soils in the Mexican highlands are rich in mineral 

 phosphates and potash, which slowly become 

 available as plant food and form the chief diet 

 of the dahlia. 



The soils in various parts of my garden are so 

 unlike that each must be treated differently. So 

 it must be with the soils in the gardens of my 

 readers. 



It is safe to say, however, that the average 

 soil is deficient in phosphates where dahlias are 

 to be grown: and this substance may in prac- 

 tically all cases be generously added. "Whether 

 phosphoric acid is derived from animal or 

 mineral sources, the chemical analysis is always 

 the same; but the different mediums which con- 

 tain it vary in percentage of content. 



"Superphosphates" are merely phosphates 



