SOIL PREPARATION 71 
ing the soil. Furthermore, the grower must not lose 
sight of the fact that a properly handled greenhouse soil 
improves in its physical properties from year to year. 
This is particularly true of the heavier types. 
In greenhouses covering thousands of square feet of 
land, soil renewal is quite out of the question and rarely 
practiced. To take out the old soil and bring in the new 
is an exceedingly expensive operation, the cost far sur- 
passing that of sterilization. The expense of soil 
preparation outside of the greenhouse should also be 
considered before one decides to make frequent renewals. 
Fig. 27.—Manure is usually placed in compost piles near the houses. 
(In this instance, mushroom houses.) 
Composting.—In many of the smaller greenhouses 
there will always be more or less necessity for the chang- 
ing of soils, and the managers should have a thorough 
knowledge of the principles and practice of composting. 
Horse manure is almost universally employed in com- 
posting (Fig. 27), although cow manure is often used for 
this purpose by florists. To make composting effective, 
three things must be accomplished: (1) The fiber of the 
