394 VEGETABLE FORCING 



growth is not expected until March or even April, when 

 the sun furnishes the required heat. Crops may be practi- 

 cally matured in the fall, when they are covered with 

 sash merely as a matter of protection until the vegetables 

 are sold. 



Again, sash may be used for a period more or less 

 definite in the spring, simply to advance the crops until 

 no protection of any kind is needed, and if desired both 

 the glass and the frames may be removed and all of the 

 ground devoted to the crops. This plan is generally used 

 from Norfolk southward. 



In the colder parts of the country it is often an ad- 

 vantage to heat the frames. Ordinary hotbeds (Figs. 136 

 and 137), varying in depth of manure from a foot to 3 

 feet, are in common use for a great variety of purposes. 

 A coil or two of steam or hot water pipes are often placed 

 in frames, and this plan is gaining friends every year over 

 the old plan of heating with manure. The temperature of 

 the frames may be better controlled with steam than with 

 manure, and the cost of heating the frames is often less. 



Fertilizing. The principles involved in the feeding of 

 greenhouse crops (Chapters IV and V) are the same as 



Fig. 136. Surface hotbed. Note notched block for supporting sash. 



