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 
