188 THE PRINCIPLES OF FLORICULTURE 



Of the necessary elements required by plants, all are 

 present in most soils in sufficient quantities for healthy 

 growth except nitrogen, phosphorus and potassium. It is 

 with these three elements, therefore, that the student of 

 fertilizer problems for greenhouse plants must deal. 



158. Preparation of greenhouse soil. As is so fre- 

 quently stated, culture of plants under glass is intensive 

 agriculture. The area is limited, and the greatest possible 

 production should come from the least possible ground 

 area. Hence, every inch of soil should not only contain 

 the maximum amount of nourishment, but it should be 

 in such a physical condition that the plant food will 

 quickly become available. The florist cannot have in his 

 soil the large quantities of unavailable plant food which 

 the fruit-grower possesses. He must so treat the soil 

 that the insoluble compounds will be largely soluble 

 when put into the houses. In other words, he should 

 reduce to a minimum the bulk of soil in which he is to 

 grow his crops throughout the season. This is necessary, 

 not alone because of the added expense of handling large 

 quantities of soil, but because in forcing plants into bloom 

 it is essential that soil, temperature and moisture be under 

 quick control. 



159. Length of time required to prepare soils for green- 

 house work. It is necessary to begin the preparation 

 of the soil a considerable period, usually a year, before 

 it is to be used. This is because of the length of time 

 required to render certain naturally insoluble, fertilizing 

 elements available for plant food, and to decompose thor- 

 oughly artificial fertilizing elements. Climatic changes, 

 especially freezing, are powerful agents in the preparation 

 of the soil, and the more it is subjected to the action of 

 the frost, the better are the results. 



