SOILS 53 



chapter, chemical changes are very rapid in greenhouse 

 soils, and with the perfect cultural conditions that are 

 maintained in well-managed houses there never should be 

 any deficiency of soluble plant food. See Chapter IV on 

 Manures, Fertilizers and Lime. 



Depth. Greenhouse soils vary in depth from 6 to 15 

 inches, and even greater depth may be found in some of 

 the soils used in the Boston district. Very deep soils hold 

 more water, of course, than do those of medium depth, 

 and this is probably their greatest advantage. Exceed- 

 ingly heavy crops have been grown in soils ranging from 

 6 to 8 inches in depth, so that it is not so much a question 

 of depth as of perfection of all other cultural require- 

 ments, for well-prepared shallow soils give better results 

 than poorly-prepared deep ones. Although very deep 

 soils require less frequent watering, they are more ex- 

 pensive to prepare for planting because of the necessity of 

 spading, or even trenching in some instances. 



Drainage. It is sometimes necessary to tile drain 

 greenhouse soils, although the necessity for drainage is 

 never so great as in the uncovered open field. When tiles 

 must be used they should also be available for steam 

 sterilization, and they may be used for sub-irrigation. 

 See pages 97, 155. If suitable soils are selected for vege- 

 table forcing there will seldom be any necessity for 

 artificial drainage. 



Muck soil. Pure muck soil is not adapted to the forc- 

 ing of the standard greenhouse vegetables, except head 

 lettuce, but when mixed with heavier soils the organic 

 content has an ameliorating influence. A vegetable 

 grower in Pennsylvania built a modern house covering 

 two acres of Dekalb gravelly loam, and then hauled muck 

 several hundred yards and spread it to a depth of 4 or 5 

 inches over the entire area of the greenhouse. The soil 

 was plowed and harrowed until the muck was thoroughly 

 incorporated. The splendid crops grown in that house 



